Date: 03/28/2016 // 0 Comments
Sometimes the most harmless gift for a small child can greatly upset him. Having bought a radio-controlled car, many people do not think that most of these toys operate at the same frequency. And if your child already has a similar toy, then a small incident may happen: the machine will respond to a remote control that is not its original one. If there are two children in the family and the frequency of radio-controlled cars coincides, then constant hysterics will be guaranteed. A counter question arises, how to change the frequency in the remote control and the model on Chinese radio-controlled cars? Today we will try to solve a similar problem and tell you how to change the frequency of a radio-controlled car.
Before tuning the frequency, you need to do three things:
Adjusting the frequency of a Chinese machine without special equipment is a delicate matter and will require patience and a little time. First of all, we open the radio-controlled car and find a coil covered with wax or paraffin on the board.
We unscrew the core until the machine stops responding to signals from the nearby remote control.
We fix the FORWARD button and very smoothly unscrew the core of the remote control coil until the moment when the machine responds to the remote control signal. Then we move a little away from the machine at a distance of 3-5 m. Most likely, now the machine at this distance will not respond to the remote control, we continue to very slowly unscrew the core.
We achieve stable operation at a distance of 3-5m, and similarly gradually increase the distance to 20m. When the machine works stably at a distance of 20 m, fill the coil on the machine board with silicone. And we assemble the model.
We adjust all the coils very smoothly; there is no need to put pressure on the core because The plastic of the coil is very soft and the core can easily fall inside.
This completes the change in frequency of the radio-controlled car. It is necessary to take into account that in this way it is unlikely to be possible to adjust more than one pair of machines.
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Wheel with negative camber angle.
Camber angle is the angle between the vertical axis of the wheel and the vertical axis of the car when you look from the front or rear of the car. If the top of the wheel is further outward than the bottom of the wheel, it is called positive camber. If the bottom of the wheel is further outward than the top of the wheel, it is called negative camber.
The camber angle affects the vehicle's handling characteristics. As a general rule, increasing negative camber improves grip on that wheel when cornering (within certain limits). This is because it gives us a tire with better distribution of cornering forces, a more optimal angle to the road, increasing the contact patch and transmitting forces through the vertical plane of the tire rather than lateral force through the tire. Another reason for using negative camber is the tendency of the rubber tire to roll relative to itself when cornering. If a wheel has zero camber, the inside edge of the tire's contact patch begins to rise from the ground, thereby reducing the contact patch area. By using negative camber, this effect is reduced, thus maximizing the tire's contact patch.
On the other hand, for maximum straight-line acceleration, maximum grip will be obtained when the camber angle is zero and the tire tread is parallel to the road. Proper camber angle distribution is a major factor in suspension design, and must include not only an idealized geometric model, but also the actual behavior of the suspension components: flex, distortion, elasticity, etc.
Most cars have some form of double wishbone suspension, which allows you to adjust the camber angle (as well as the camber gain).
Camber gain is a measure of how the camber angle changes as the suspension is compressed. This is determined by the length of the control arms and the angle between the upper and lower control arms. If the upper and lower control arms are parallel, the camber will not change as the suspension is compressed. If the angle between the suspension arms is significant, the camber will increase as the suspension is compressed.
A certain amount of camber gain is useful in keeping the tire surface parallel to the ground when the vehicle leans into a corner.
Note: The suspension arms should either be parallel or should be closer together on the inside (car side) than on the wheel side. Having suspension arms that are closer together on the wheel side rather than on the car side will result in radically different camber angles (the car will behave erratically).
The increase in camber will determine how the car's roll center behaves. The car's roll center, in turn, determines how weight transfer will occur when cornering, and this has a significant impact on handling (see more on this below).
The caster angle (or caster) is the angular deviation from the vertical axis of the wheel suspension in a car, measured in the longitudinal direction (the angle of the steering axis of the wheel when viewed from the side of the car). This is the angle between the joint line (in a car, the imaginary line that runs through the center of the upper ball joint to the center of the lower ball joint) and the vertical. Caster angle can be adjusted to optimize vehicle handling in certain driving situations.
The wheel pivot points are angled such that a line drawn through them intersects the road surface slightly in front of the wheel contact point. The purpose of this is to provide some degree of self-centering in the steering - the wheel rolls behind the wheel's steering axis. This makes the car easier to control and improves its stability on straight roads (reducing the tendency to deviate from the trajectory). Excessive caster angles will make steering feel heavier and less responsive, however, in off-road competition, higher caster angles are used to improve camber gain when cornering.
Toe is the symmetrical angle that each wheel makes with the longitudinal axis of the car. Toe-in is when the front of the wheels is directed towards the central axis of the car.
Front toe angle
Basically, increased toe-in (the fronts of the wheels are closer together than the rears of the wheels) provides more straight-line stability at the cost of some sluggish cornering response, as well as slightly increased drag since the wheels are now running slightly sideways.
Spreading out the front wheels will result in more responsive steering and faster corner entry. However, front toe usually means a less stable car (more jerky).
Rear toe angle
Your vehicle's rear wheels should always be aligned with some degree of toe (although 0 degrees toe is acceptable in some conditions). Basically, the greater the rear toe-in, the more stable the car will be. However, keep in mind that increasing the toe angle (front or rear) will result in reduced speed on straightaways (especially when using stock motors).
Another related concept is that toe that is suitable for a straight section will not be suitable for a turn, since the inside wheel must follow a smaller radius than the outside wheel. To compensate for this, steering linkages usually follow more or less the Ackermann principle for steering, modified to suit the characteristics of a particular car model.
The Ackermann principle in steering is a geometric arrangement of steering rods of a car model, designed to solve the problem of the need for the inner and outer wheels to follow different radii during a turn.
When a car turns, it follows a path that is part of its turning circle, the center of which is somewhere along a line through the rear axle. The rotated wheels should be tilted so that they both make an angle of 90 degrees with a line drawn from the center of the circle through the center of the wheel. Because the wheel on the outside of the turn will be on a larger radius than the wheel on the inside of the turn, it must be turned to a different angle.
The Ackermann steering principle automatically adjusts this by moving the steering joints inward so that they are on a line drawn between the steering axis of the wheel and the center of the rear axle. The steering joints are connected by a rigid rod, which in turn is part of the steering mechanism. This arrangement ensures that at any angle of rotation, the centers of the circles along which the wheels follow will be at one common point.
The slip angle is the angle between the actual path of the wheel and the direction in which it is pointing. The slip angle results in a lateral force perpendicular to the direction of wheel motion - corner force. This angular force increases approximately linearly for the first few degrees of slip angle, and then increases nonlinearly until it reaches a maximum, after which it begins to decrease (as the wheel begins to slip).
A non-zero slip angle occurs due to tire deformation. As the wheel rotates, the frictional force between the tire's contact patch and the road causes individual tread "elements" (infinitesimal portions of the tread) to remain stationary relative to the road.
This deflection of the tire results in an increase in slip angle and corner force.
Since the forces that act on the wheels from the weight of the car are distributed unevenly, the lateral slip angle of each wheel will be different. The relationship between the slip angles will determine the behavior of the car in a given turn. If the ratio of front slip angle to rear slip angle is greater than 1:1, the vehicle will be susceptible to understeer, and if the ratio is less than 1:1, it will promote oversteer. The actual instantaneous slip angle depends on many factors, including road surface conditions, but a vehicle's suspension can be designed to provide specific dynamic characteristics.
The main means of adjusting the resulting lateral slip angles is to change the relative front-to-back roll by adjusting the amount of front and rear lateral weight transfer. This can be achieved by changing the height of the roll centers, or by adjusting the roll severity, by changing the suspension, or by adding anti-roll bars.
Weight transfer refers to the redistribution of weight supported by each wheel during acceleration (longitudinal and lateral). This includes accelerating, braking or turning. Understanding weight transfer is critical to understanding vehicle dynamics.
Weight transfer occurs as the center of gravity (CoG) shifts during vehicle maneuvers. Acceleration causes the center of mass to rotate around a geometric axis, resulting in a shift in the center of gravity (CoG). Front-to-rear weight transfer is proportional to the ratio of the vehicle's center of gravity height to the car's wheelbase, and lateral weight transfer (front and rear total) is proportional to the vehicle's center of gravity height to wheelbase ratio, as well as the height of its roll center (explained below).
For example, when a car accelerates, its weight is transferred towards the rear wheels. You can observe this as the car noticeably leans backwards, or "squats." Conversely, when braking, weight is transferred towards the front wheels (the nose “dives” towards the ground). Likewise, during changes in direction (lateral acceleration), weight is transferred to the outside of the turn.
Weight transfer causes a change in the available traction on all four wheels when the vehicle brakes, accelerates, or turns. For example, since weight transfer occurs forward when braking, the front wheels do most of the braking work. This shift in "work" to one pair of wheels from the other results in a loss of overall available traction.
If lateral weight transfer reaches the wheel load at one end of the vehicle, the inside wheel at that end will lift, causing a change in handling characteristics. If this weight transfer reaches half the vehicle's weight, it begins to roll over. Some large trucks will roll over before sliding, but road cars usually only roll over when they go off the road.
A car's roll center is an imaginary point marking the center around which the car rolls (in corners) when viewed from the front (or rear).
The position of the geometric roll center is dictated solely by the suspension geometry. The official definition of roll center is: "The point on the cross section through any pair of wheel centers at which lateral forces can be applied to the sprung mass without causing suspension roll."
The value of the roll center can only be estimated when the center of mass of the vehicle is taken into account. If there is a difference between the positions of the center of mass and the center of roll, then a “moment arm” is created. When a car experiences lateral acceleration in a corner, the roll center moves up or down, and the size of the moment arm, combined with the stiffness of the springs and anti-roll bars, dictates the amount of roll in the corner.
The geometric roll center of a vehicle can be found using the following basic geometric procedures when the vehicle is in a static state: 
Draw imaginary lines parallel to the suspension arms (red). Then draw imaginary lines between the intersection points of the red lines and the lower centers of the wheels, as shown in the picture (in green). The point where these green lines intersect is the roll center.
You need to note that the roll center moves when the suspension compresses or lifts, so it is actually the instantaneous roll center. How much this roll center moves as the suspension compresses is determined by the length of the control arms and the angle between the upper and lower control arms (or adjustable suspension links).
As the suspension is compressed, the roll center rises higher and the moment arm (the distance between the roll center and the vehicle's center of gravity (CoG in the figure)) will decrease. This will mean that when the suspension is compressed (for example, when cornering), the car will have less tendency to roll (which is good if you don't want to roll over).
When you use high-grip (foam rubber) tires, you must set the suspension arms so that the roll center rises significantly as the suspension is compressed. Road ICE cars have very aggressive suspension angles to raise the roll center during cornering and prevent rollovers when using foam tires.
The use of parallel, equal-length suspension arms results in a fixed roll center. This means that when the car is tilted, the moment arm will force the car to roll more and more. As a general rule, the higher your vehicle's center of gravity, the higher its roll center must be to avoid rollovers.
"Bump Steer" is the tendency of a wheel to turn as it moves up the suspension travel. On most vehicles, the front wheels typically experience toe (the front of the wheel moves outward) as the suspension is compressed. This allows for roll understeer (when you hit a bump in a corner, the car tends to straighten out). Excessive "bump steer" increases tire wear and makes the car jerky on uneven roads.
"Bump Steer" and roll center
On a bump, both wheels rise together. When banking, one wheel goes up and the other goes down. This usually produces more toe in on one wheel and more toe out in the other wheel, thus producing a turning effect. In simple analysis you can simply assume that roll steering is similar to "bump steer", but in practice things like the anti-roll bar have an effect that changes this.
"Bump steer" can be increased by raising the outer joint or lowering the inner joint. Minor adjustments are usually required.
Understeer is a condition of a car's controllability in a turn, in which the car's circular path has a noticeably larger diameter than the circle indicated by the direction of the wheels. This effect is the opposite of oversteer, and in simple terms, understeer is a condition in which the front wheels do not follow the path set by the driver for cornering, but instead follow a straighter path.
This is also often called pushing out or refusing to turn. The car is called “clamped” because it is stable and far from the tendency to skid.
Just like oversteer, understeer has many sources, such as mechanical clutch, aerodynamics and suspension.
Traditionally, understeer occurs when the front wheels have insufficient grip during a turn, so the front end of the car has less mechanical grip and cannot follow the line through the turn.
Camber angles, ground clearance and center of gravity are important factors that determine the understeer/oversteer condition.
It is a general rule that manufacturers deliberately tune cars to have slight understeer. If a car has slight understeer, it will be more stable (within the driver's average ability) during sudden changes in direction.
How to tune your car to reduce understeer
You should start by increasing the negative camber of the front wheels (never exceed -3 degrees for on-road vehicles and 5-6 degrees for off-road vehicles).
Another way to reduce understeer is to reduce the negative camber of the rear wheels (it should always be<=0 градусов).
Another way to reduce understeer is to stiffen or remove the front sway bar (or stiffen the rear sway bar).
It is important to note that any adjustments are subject to compromise. The car has a limited amount of total grip that can be distributed between the front and rear wheels.
A car oversteers when the rear wheels do not follow the front wheels, but instead slide toward the outside of the turn. Oversteer can lead to skidding.
A car's tendency to oversteer is influenced by several factors, such as mechanical clutch, aerodynamics, suspension and driving style.
The limit of oversteer occurs when the rear tires exceed their lateral grip limit during a turn before the front tires do, thereby causing the car's rear to point toward the outside of the corner. In general, oversteer is a condition where the slip angle of the rear tires exceeds the slip angle of the front tires.
Rear-wheel drive cars are more prone to oversteer, especially when using the throttle in tight corners. This is because the rear tires must withstand lateral forces and engine thrust.
A car's tendency to oversteer usually increases when the front suspension is softened or the rear suspension is stiffened (or when a rear anti-roll bar is added). Camber angles, ground clearance and tire temperature rating can also be used to adjust the car's balance.
A car with oversteer may also be called "loose" or "unclamped".
How do you differentiate between oversteer and understeer?
When you go into a corner, oversteer is when the car turns sharper than you expect, and understeer is when the car turns less than you expect.
Oversteer or understeer, that is the question
As mentioned earlier, any adjustments are a matter of compromise. The car has limited grip that can be distributed between the front and rear wheels (this can be expanded using aerodynamics, but that's another story).
All sports cars develop a higher lateral (ie side slip) speed than is determined by the direction in which the wheels are pointing. The difference between the circle in which the wheels roll and the direction in which they point is the slip angle. If the slip angles of the front and rear wheels are the same, the car has neutral handling balance. If the slip angle of the front wheels exceeds the slip angle of the rear wheels, the car is said to have understeer. If the slip angle of the rear wheels exceeds the slip angle of the front wheels, the car is said to have oversteer.
Just remember that an understeering car hits the guardrail with its front end, an oversteering car hits the guardrail with its rear end, and a neutral handling car hits the guardrail with both ends at the same time.
Any vehicle can experience understeer or oversteer depending on road conditions, speed, available traction and driver input. Vehicle design, however, tends to reach an individual "limit" condition where the vehicle reaches and exceeds its traction limits. “Marginal understeer” refers to a vehicle that, due to design features, tends to understeer when angular accelerations exceed tire grip.
The ultimate handling balance is a function of front/rear relative roll resistance (suspension stiffness), front/rear weight distribution, and front/rear tire grip. A car with a heavy front end and low rear roll resistance (due to soft springs and/or low stiffness or lack of rear anti-roll bars) will tend to experience extreme understeer: its front tires, being more heavily loaded even when static, will reach the limits of their grip earlier than the rear tires and thus develop larger slip angles. Front-wheel drive cars are also prone to understeer because not only do they typically have a heavy front end, but sending power to the front wheels also reduces their available grip for turning. This often results in a "shudder" effect on the front wheels as grip changes unexpectedly due to the transfer of power from the engine to the road and steering.
Although understeer and oversteer can both cause a loss of control, many manufacturers design their cars for extreme understeer on the assumption that it is easier for the average driver to control than extreme oversteer. Unlike extreme oversteer, which often requires several steering adjustments, understeer can often be reduced by reducing speed.
Understeer can not only occur during acceleration in a corner, it can also occur during hard braking. If the brake balance (braking force on the front and rear axle) is too forward, it can cause understeer. This is caused by the front wheels locking and loss of effective control. The opposite effect can also occur; if the brake balance is too far back, the rear end of the car will skid.
Athletes on asphalt surfaces generally prefer a neutral balance (with a slight tendency towards understeer or oversteer, depending on the track and driving style), as understeer and oversteer lead to a loss of speed during cornering. In rear-wheel drive cars, understeer generally works better because the rear wheels need some available grip to accelerate the car out of corners.
Spring stiffness is a tool for adjusting the vehicle's ground clearance and its suspension position. Spring stiffness is a coefficient used to measure the amount of compression resistance.
Springs that are too hard or too soft will effectively result in the car having no suspension at all.
Spring stiffness referred to the wheel (Wheel rate)
The spring rate referred to the wheel is the effective spring rate when measured at the wheel.
The spring rate applied to the wheel is usually equal to or significantly less than the spring rate itself. Typically, the springs are mounted on the control arms or other parts of the suspension articulation system. Assuming that as the wheel moves 1 inch, the spring moves 0.75 inches, the leverage ratio would be 0.75:1. The spring rate referred to the wheel is calculated by squaring the lever ratio (0.5625), multiplying by the spring rate and by the sine of the spring angle. The ratio is squared due to two effects. The ratio is applied to force and distance traveled.
Suspension travel is the distance from the bottom of the suspension travel (when the car is on a stand and the wheels are hanging freely) to the top of the suspension travel (when the car's wheels can no longer go higher). If a wheel reaches its lower or upper limit, it can cause serious control problems. "Reaching the limit" can be caused by the suspension, chassis, etc. moving beyond its limits. or touching the road with the body or other components of the vehicle.
Damping is the control of motion or vibration through the use of hydraulic shock absorbers. Damping controls the speed and resistance of a vehicle's suspension. A car without damping will oscillate up and down. With the help of suitable damping, the car will return back to its normal state in a minimum amount of time. Damping in modern vehicles can be controlled by increasing or decreasing the fluid viscosity (or piston bore size) in the shock absorbers.
Anti-dive and anti-squat are expressed as a percentage and refer to the dive of the front of the car when braking and the squat of the rear of the car when accelerating. They can be considered twins for braking and acceleration, while the roll center height works in corners. The main reason for their difference is the different design goals for the front and rear suspension, while the suspension is usually symmetrical between the right and left sides of the car.
The percentage of anti-dive and anti-squat is always calculated relative to the vertical plane that intersects the vehicle's center of gravity. Let's look at anti-squat first. Determine the location of the rear instantaneous center of the suspension when looking at the car from the side. Draw a line from the tire contact patch through the instantaneous center, this will be the force vector of the wheel. Now draw a vertical line through the center of gravity of the car. Anti-squat is the ratio between the height of the intersection point of the wheel force vector and the height of the center of gravity, expressed as a percentage. An anti-squat value of 50% would mean that the force vector during acceleration passes halfway between the ground and the center of gravity. 
Anti-dive is the counterpart of anti-squat and works for the front suspension during braking.
The circle of forces is a useful way to think about the dynamic interaction between a car's tire and the road surface. In the diagram below, we are looking at the wheel from above, so the road surface lies in the x-y plane. The car to which the wheel is attached moves in the positive y direction. 
In this example, the car will turn right (ie the positive x direction is towards the center of the turn). Note that the plane of rotation of the wheel is at an angle to the actual direction in which the wheel is moving (in the positive y direction). This angle is the slip angle.
The limit of the value of F is limited by the dotted circle, F can be any combination of the components Fx (turn) and Fy (acceleration or braking) that does not exceed the dotted circle. If the combination of forces Fx and Fy goes outside the circle, the tire loses traction (you slide or skid).
In this example, the tire creates a force component in the x direction (Fx) which, when transmitted to the vehicle's chassis through the suspension system in combination with similar forces from the remaining wheels, will cause the vehicle to turn to the right. The diameter of the force circle, and therefore the maximum horizontal force a tire can produce, is influenced by many factors, including tire design and condition (age and temperature range), road surface quality, and vertical wheel load.
A car that understeers has an accompanying instability mode called critical speed. As you approach this speed, the control becomes increasingly sensitive. At critical speed, the yaw rate becomes infinite, that is, the car continues to turn even with the wheels straightened. At speeds above the critical speed, simple analysis shows that the steering angle must be reversed (counter-steering). A car that understeers is not affected by this, which is one of the reasons why high-speed cars are tuned to understeer.
A car that does not suffer from oversteer or understeer when driven to its limit has neutral balance. It seems intuitive that athletes would prefer a little oversteer to spin the car around a corner, but this is not commonly used for two reasons. Early acceleration, as soon as the car passes the apex of the turn, allows the car to gain additional speed on the subsequent straight section. The driver who accelerates earlier or faster has a big advantage. The rear tires require some excess grip to accelerate the car in this critical phase of the turn, while the front tires can dedicate all their grip to the turn. Therefore, the car should be tuned with a slight tendency to understeer or should be slightly "pinched". Also, a car that oversteers is jerky, increasing the likelihood of losing control during long events or when reacting to an unexpected situation.
Please note that this only applies to competition on road surfaces. Competitions on clay are a completely different story.
Some successful drivers prefer a little oversteer in their cars, preferring a car that's quieter and easier to corner. It should be noted that judgment about the handling balance of a car model is not objective. Driving style is a major factor in the apparent balance of a car. Therefore, two drivers with identical car models often use them with different balance settings. And both can call the balance of their cars "neutral."
Before moving on to the description of the receiver, let's consider the frequency distribution for radio control equipment. And let's start here with laws and regulations. For all radio equipment, the distribution of frequency resources in the world is carried out by the International Committee on Radio Frequencies. It has several subcommittees on zones of the globe. Therefore, in different areas of the Earth, different frequency ranges are allocated for radio control. Moreover, the subcommittees only recommend frequency allocations to the states in their zone, and the national committees, as part of the recommendations, introduce their own restrictions. In order not to inflate the description beyond measure, let us consider the distribution of frequencies in the American region, Europe and in our country.
In general, the first half of the VHF radio wave range is used for radio control. In the American region, these are the bands 50, 72 and 75 MHz. Moreover, 72 MHz is exclusively for flying models. In Europe, the bands allowed are 26, 27, 35, 40 and 41 MHz. The first and last in France, the rest throughout the EU. In our native country, the permitted range is 27 MHz and, since 2001, a small portion of the 40 MHz range. Such a narrow distribution of radio frequencies could hinder the development of radio modeling. But, as Russian thinkers correctly noted back in the 18th century, “the severity of laws in Rus' is compensated by loyalty to their non-compliance.” In reality, in Russia and in the territory of the former USSR, the 35 and 40 MHz bands according to the European layout are widely used. Some try to use American frequencies, and sometimes successfully. However, most often these attempts are thwarted by interference from VHF radio broadcasting, which has been using precisely this range since Soviet times. In the 27-28 MHz range, radio control is allowed, but can only be used for ground models. The fact is that this range is also given over to civil communications. There are a huge number of “Wokie-talkie” stations operating there. Near industrial centers, the interference situation in this range is very bad.
The 35 and 40 MHz bands are the most acceptable in Russia, and the latter is permitted by law, although not all of it. Of the 600 kilohertz of this range, only 40 have been legalized in our country, from 40.660 to 40.700 MHz (see Decision of the State Committee for Radio Frequencies of Russia dated March 25, 2001, Protocol N7/5). That is, out of 42 channels, only 4 are officially allowed in our country. But they may also contain interference from other radio media. In particular, about 10,000 Len radio stations were produced in the USSR for use in the construction and agro-industrial complex. They operate in the range 30 - 57 MHz. Most of them are still actively exploited. Therefore, no one is safe from interference here either.
Note that the legislation of many countries allows the use of the second half of the VHF range for radio control, but such equipment is not commercially produced. This is due to the complexity in the recent past of the technical implementation of frequency generation in the range above 100 MHz. Currently, the element base makes it possible to easily and cheaply form a carrier up to 1000 MHz, however, the inertia of the market is still hindering the mass production of equipment in the upper part of the VHF range.
To ensure reliable untuned communication, the carrier frequency of the transmitter and the receiving frequency of the receiver must be sufficiently stable and switchable to ensure joint interference-free operation of several sets of equipment in one place. These problems are solved by using a quartz resonator as a frequency-setting element. To be able to switch frequencies, the quartz is made replaceable, i.e. a niche with a connector is provided in the transmitter and receiver housings, and the quartz of the desired frequency is easily changed directly in the field. In order to ensure compatibility, frequency ranges are divided into separate frequency channels, which are also numbered. The interval between channels is defined as 10 kHz. For example, a frequency of 35.010 MHz corresponds to 61 channels, 35.020 to 62 channels, and 35.100 to 70 channels.
The joint operation of two sets of radio equipment on the same field on the same frequency channel is in principle impossible. Both channels will continuously glitch regardless of whether they are in AM, FM or PCM mode. Compatibility is achieved only by switching equipment sets to different frequencies. How is this achieved practically? Everyone who arrives at an airfield, highway or body of water is obliged to look around to see if there are other modelers there. If they are, you need to go around everyone and ask in what range and on what channel their equipment operates. If there is at least one modeler whose channel coincides with yours, and you do not have replaceable crystals, negotiate with him to turn on the equipment only one at a time, and in general, stay close to him. At competitions, the frequency compatibility of the equipment of different participants is the concern of the organizers and judges. Abroad, to identify channels, it is customary to attach special pennants to the transmitter antenna, the color of which determines the range, and the numbers on it indicate the number (and frequency) of the channel. However, it is better for us to adhere to the order described above. Moreover, since transmitters on adjacent channels can interfere with each other due to the sometimes occurring synchronous drift of the transmitter and receiver frequencies, careful modelers try not to work in the same field on adjacent frequency channels. That is, channels are chosen so that there is at least one free channel between them.
For clarity, here are tables of channel numbers for the European layout:
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Channels that are legally permitted for use in Russia are highlighted in bold. In the 27 MHz band, only preferred channels are shown. In Europe, the channel spacing is 10 kHz.
And here is the layout table for America:
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In America, they have their own numbering, and the interchannel interval is already 20 kHz.
To fully understand quartz resonators, we will run a little ahead and say a few words about receivers. All receivers in commercially produced equipment are built according to a superheterodyne circuit with one or two conversions. We won’t explain what this is, but anyone familiar with radio engineering will understand. So, frequency formation in the transmitter and receiver of different manufacturers occurs differently. In a transmitter, a quartz resonator can be excited at the fundamental harmonic, after which its frequency doubles or triples, and maybe even at the 3rd or 5th harmonic. In the receiver local oscillator, the excitation frequency can be either higher than the channel frequency or lower by the intermediate frequency. Double conversion receivers have two intermediate frequencies (typically 10.7 MHz and 455 kHz), so the number of possible combinations is even greater. Those. the frequencies of the quartz resonators of the transmitter and receiver never coincide, both with the frequency of the signal that will be emitted by the transmitter, and with each other. Therefore, equipment manufacturers have agreed to indicate on the quartz resonator not its real frequency, as is customary in other radio engineering, but its purpose: TX - transmitter, RX - receiver, and the frequency (or number) of the channel. If the quartz of the receiver and transmitter are swapped, the equipment will not work. True, there is one exception: some devices with AM can also work with mixed quartz, provided that both quartz are on the same harmonic, but the frequency on the air will be 455 kHz higher or lower than that indicated on the quartz. However, the range will decrease.
It was noted above that a transmitter and receiver from different manufacturers can work together in PPM mode. What about quartz resonators? Whose should I put where? We can recommend installing a native quartz resonator in each device. Quite often this helps. But not always. Unfortunately, tolerances for the manufacturing accuracy of quartz resonators from different manufacturers vary significantly. Therefore, the possibility of joint operation of specific components from different manufacturers and with different quartz can only be established experimentally.
And further. In principle, in some cases it is possible to install quartz resonators from another manufacturer on equipment from one manufacturer, but we do not recommend this. A quartz resonator is characterized not only by frequency, but also by a number of other parameters, such as quality factor, dynamic resistance, etc. Manufacturers design equipment for a specific type of quartz. The use of another may generally reduce the reliability of the radio control.
Brief summary:
As we have already indicated, a receiver is installed on the controlled model.
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Radio control receivers are designed to work with only one type of modulation and one type of coding. Thus, there are AM, FM and PCM receivers. Moreover, RSM varies from company to company. If on the transmitter you can simply switch the encoding method from PCM to PPM, then the receiver must be replaced with another.
The receiver is made according to a superheterodyne circuit with two or one conversion. Receivers with two conversions have, in principle, better selectivity, i.e. better filter out interference with frequencies outside the working channel. As a rule, they are more expensive, but their use is justified for expensive, especially flying models. As already noted, quartz resonators for the same channel for receivers with two and one conversion are different and not interchangeable.
If you arrange receivers in increasing order of noise immunity (and, unfortunately, price), then the series will look like this:
When choosing a receiver for your model from this range, you need to take into account its purpose and cost. From the point of view of noise immunity, it is not bad to install a PCM receiver on the training model. But by driving the model into concrete during training, you will lighten your wallet by a much greater amount than with a single-conversion FM receiver. Likewise, if you install an AM receiver or a simplified FM receiver on a helicopter, you will seriously regret it later. Especially if you fly near large cities with developed industry.
The receiver can only operate in one frequency range. Converting a receiver from one band to another is theoretically possible, but it is hardly justified economically, since this work is very labor intensive. It can only be carried out by highly qualified engineers in a radio laboratory. Some frequency ranges for receivers are divided into subbands. This is due to the large bandwidth (1000 kHz) with a relatively low first IF (455 kHz). In this case, the main and mirror channels fall into the passband of the receiver preselector. In this case, it is generally impossible to ensure selectivity over the mirror channel in a receiver with one conversion. Therefore, in the European layout, the 35 MHz band is divided into two sections: from 35.010 to 35.200 - this is the “A” subband (channels 61 to 80); from 35.820 to 35.910 - subband “B” (channels 182 to 191). In the American layout, two subbands are also allocated in the 72 MHz band: from 72.010 to 72.490, the “Low” subband (channels 11 to 35); from 72.510 to 72.990 - “High” (channels 36 to 60). Different receivers are available for different subbands. In the 35 MHz range they are not interchangeable. In the 72 MHz range they are partially interchangeable on frequency channels near the border of the subbands.
The next sign of the type of receiver is the number of control channels. Receivers are available with a number of channels from two to twelve. At the same time, circuitry, i.e. based on their “gibles”, receivers for 3 and 6 channels may not differ at all. This means that a three-channel receiver may have decoded signals of the fourth, fifth and sixth channels, but there are no connectors on the board for connecting additional servos.
To make full use of the connectors, receivers often do not have a separate power connector. In the case when servos are not connected to all channels, the power cable from the on-board switch is connected to any free output. If all outputs are enabled, then one of the servos is connected to the receiver through a splitter (the so-called Y-cable), to which the power is connected. When the receiver is powered from a power battery through a speed controller with the BEC function, there is no need for a special power cable at all - the power is supplied through the signal cable of the speed controller. Most receivers are designed to operate at a nominal voltage of 4.8 volts, which corresponds to a battery of four nickel-cadmium batteries. Some receivers allow the use of on-board power from 5 batteries, which improves the speed and power parameters of some servos. Here you need to be attentive to the operating instructions. Receivers that are not designed for increased supply voltage may burn out in this case. The same applies to steering gears, whose service life may drop sharply.
Receivers for ground models are often produced with a shortened wire antenna, which is easier to place on the model. It should not be lengthened, since this will not increase, but rather reduce the range of reliable operation of the radio control equipment.
For models of ships and cars, receivers in a waterproof housing are available:
Receivers with a synthesizer are available for athletes. There is no replaceable quartz, and the working channel is set by multi-position switches on the receiver body:
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With the advent of the class of ultra-light flying models - indoor ones, the production of special very small and light receivers began:
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These receivers often do not have a rigid polystyrene housing and are housed in heat-shrinkable PVC tubing. They can be built into an integrated speed controller, which generally reduces the weight of on-board equipment. If there is a tough competition for grams, it is allowed to use miniature receivers without a housing at all. Due to the active use of lithium-polymer batteries in ultra-light flying models (their specific capacity is several times greater than that of nickel batteries), specialized receivers have appeared with a wide range of supply voltage and a built-in speed controller:
Let's summarize what was said above.
As a rule, the receiver is housed in a compact housing and is made on a single printed circuit board. A wire antenna is attached to it. The case has a niche with a connector for a quartz resonator and contact groups of connectors for connecting actuators, such as servos and speed controllers.
The radio signal receiver and decoder are mounted on the printed circuit board.
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A replaceable quartz resonator sets the frequency of the first (only) local oscillator. The values of intermediate frequencies are standard for all manufacturers: the first IF is 10.7 MHz, the second (the only one) is 455 kHz.
The output of each channel of the receiver decoder is connected to a three-pin connector, where, in addition to the signal signal, there are ground and power contacts. The structure of the signal is a single pulse with a period of 20 ms and a duration equal to the value of the channel pulse of the PPM signal generated in the transmitter. The PCM decoder output has the same signal as PPM. In addition, the PCM decoder contains a so-called Fail-Safe module, which allows you to bring the steering gears to a predetermined position if the radio signal is lost. More information about this is written in the article "PPM or PCM?".
Some receiver models have a special connector to provide the DSC (Direct servo control) function - direct control of servos. To do this, a special cable connects the trainer connector of the transmitter and the DSC connector of the receiver. After which, with the RF module turned off (even in the absence of quartz and a faulty RF part of the receiver), the transmitter directly controls the servos on the model. The function can be useful for ground-based debugging of the model, so as not to unnecessarily pollute the airwaves, as well as for searching for possible faults. At the same time, the DSC cable is used to measure the supply voltage of the on-board battery - this is provided for in many expensive transmitter models.
Unfortunately, receivers break down much more often than we would like. The main reasons are impacts from model crashes and strong vibrations from power plants. Most often this happens when the modeler neglects the recommendations for damping the receiver when placing the receiver inside the model. It's hard to overdo it here, and the more foam and sponge rubber you use, the better. The most sensitive element to shock and vibration is the replaceable quartz resonator. If after an impact your receiver malfunctions, try changing the quartz - in half the cases this helps.
A few words about interference on board the model and how to deal with it. In addition to interference from the air, the model itself may have sources of its own interference. They are located close to the receiver and, as a rule, have broadband radiation, i.e. They act simultaneously at all frequencies of the range, and therefore their consequences can be disastrous. A typical source of interference is a commutator traction motor. They learned to deal with its interference by powering it through special anti-interference circuits, consisting of a capacitor shunting each brush to the housing and a series-connected inductor. For powerful electric motors, separate power is used for the motor itself and the receiver from a separate, non-running battery. The stroke controller provides for optoelectronic decoupling of control circuits from power circuits. Oddly enough, brushless electric motors create no less level of interference than brushed motors. Therefore, for powerful motors it is better to use speed controllers with optical isolation and a separate battery to power the receiver.
On models with gasoline engines and spark ignition, the latter is a source of powerful interference over a wide frequency range. To combat interference, shielding is used on the high-voltage cable, the spark plug tip and the entire ignition module. Magneto ignition systems create slightly less noise than electronic ignition systems. In the latter, power is supplied necessarily from a separate battery, not from the on-board one. In addition, they use a spatial separation of on-board equipment from the ignition system and engine by at least a quarter of a meter.
The third most important source of interference is servos. Their interference becomes noticeable on large models, where many powerful servos are installed, and the cables connecting the receiver to the servos become long. In this case, it helps to put small ferrite rings on the cable near the receiver so that the cable makes 3-4 turns on the ring. You can do this yourself, or buy ready-made branded extension servo cables with ferrite rings. A more radical solution is to use different batteries to power the receiver and servos. In this case, all receiver outputs are connected to servo cables through a special device with optical isolation. You can make such a device yourself, or buy a ready-made branded one.
In conclusion, let us mention something that is not yet very common in Russia - giant models. These include flying models weighing more than eight to ten kilograms. Failure of the radio channel with the subsequent crash of the model in this case is fraught not only with material losses, which are considerable in absolute terms, but also poses a threat to the life and health of others. Therefore, the legislation of many countries obliges modellers to use complete duplication of on-board equipment on such models: i.e. two receivers, two on-board batteries, two sets of servos that control two sets of rudders. In this case, any single failure does not lead to a crash, but only slightly reduces the effectiveness of the rudders.
In conclusion, a few words to those who want to make their own radio control equipment. In the opinion of authors who have been involved in amateur radio for many years, in most cases this is not justified. The desire to save money on the purchase of ready-made serial equipment is deceptive. And the result is unlikely to please you with its quality. If you don’t have enough money even for a simple set of equipment, buy a used one. Modern transmitters become obsolete morally before they wear out physically. If you are confident in your capabilities, take a faulty transmitter or receiver at a bargain price - repairing it will still give better results than making a homemade one.
Remember that the “wrong” receiver is at most one ruined model of its own, but the “wrong” transmitter with its out-of-band radio emissions can destroy a bunch of other people’s models, which may turn out to be more expensive than its own.
In case the urge to make circuits is irresistible, first search the Internet. There is a very high probability that you will be able to find ready-made diagrams - this will save you time and avoid many mistakes.
For those who are more of a radio amateur at heart than a modeler, there is a wide field for creativity, especially where the serial manufacturer has not yet reached. Here are a few topics worth tackling yourself:
After reading articles on radio control transmitters and receivers, you were able to decide what kind of equipment you need. But some questions, as always, remained. One of them is how to buy equipment: in bulk, or in a set, which includes a transmitter, receiver, batteries for them, servos and a charger. If this is the first device in your modeling practice, it is better to buy it as a set. This automatically solves compatibility and packaging problems. Then, when your model fleet increases, you can buy additional receivers and servos separately, in accordance with the other requirements of the new models.
When using higher voltage on-board power with a five-cell battery, choose a receiver that can handle this voltage. Also pay attention to the compatibility of the separately purchased receiver with your transmitter. Receivers are produced by a much larger number of companies than transmitters.
A few words about a detail that is often neglected by novice modelers - the on-board power switch. Specialized switches are made in a vibration-resistant design. Replacing them with untested toggle switches or switches from radio equipment can cause an in-flight failure with all the ensuing consequences. Be attentive to both the main thing and the little things. There are no minor details in radio modeling. Otherwise, according to Zhvanetsky: “one wrong move and you are a father.”
Remote control of moving models is based on interaction between a person and a model. The pilot sees the position of the model in space and its speed. Using remote control equipment, he gives commands to the model’s actuators, which turn the rudders or control the engines, thereby the pilot changes the position and direction of the model’s movement in accordance with his desire. The transmission of commands from the pilot to the model occurs mostly via radio. An exception can be found only for indoor models, where infrared radiation is used along with radio, and ultrasound is also very rarely used to control underwater vehicles.
The radio control equipment consists of a transmitter, which is located by the pilot, and a receiver and actuators located on the model. This article will help you gain an understanding of how a transmitter works and which transmitter you need.
Based on the design of the controls, which are actually acted upon by the pilot’s fingers, transmitters are divided into joystick and pistol type. The first ones usually have two two-axis joysticks. Such transmitters are used to control flying models. In joystick transmitters, the handle has built-in springs that return it to the neutral position when released. As a rule, one of the directions of some kind of joystick is used to control the traction motor - it does not have a return spring. In this case, the handle is pressed with a ratchet (for airplanes) or a smooth braking plate (for helicopters). Using such transmitters, you can also successfully control floating and driving models, but special pistol-type transmitters have been invented for them. Here the steering wheel controls the direction of movement of the model, and the trigger controls its engine and brakes.
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In recent years, transmitters with a single two-axis joystick have appeared. They belong to the category of cheap devices and can be used to control both simplified flying and ground equipment. They can be used productively only at the most basic level. Transmitters with two single-axis joysticks have a similar purpose:
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To finish with design variations, let’s add a division of joystick transmitters into monoblock and modular. If the first ones are fully equipped with all components and are immediately ready for use, then the modular ones represent a basis into which the pilot, at his discretion, adds the additional controls he needs:
There are two ways to hold the transmitter. Remote control transmitters are hung around the pilot's neck using a special belt or stand. The pilot's hands rest on the transmitter body, and each joystick is controlled by two fingers - the index and thumb. This is the so-called European school. The pilot holds the handheld transmitter in his hands, and each joystick is controlled by one thumb. This manner is attributed to the American school.
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The handheld transmitter can also be held in your hands and controlled in a European way. You can also use it in a remote control version if you buy a special table-stand for it. The table is no worse than a branded one do it yourself. Such tables are also required for some remote control transmitters. Which manner is more common among us depends on the age of the pilot. Young people, according to our observations, are more inclined to American customs, and the older generation is more inclined to the conservatism of Europe.
Controlling moving models requires influencing several functions simultaneously. Therefore, radio control transmitters are made multi-channel. Let's consider the number and purpose of channels.
For cars and ship models, two channels are needed: control of the direction of movement and engine speed. Sophisticated pistol transmitters also have a third channel, which can be used to control the mixture formation of the internal combustion engine (radio needle).
To control the simplest flying models, two channels can also be used: elevators and ailerons for gliders and airplanes, or elevators and rudder. For hang gliders, roll control and motor power are used. This scheme is also used on some simple gliders - rudder and engine switching on. Such two-channel transmitters can be used for fleet models and entry-level electric aircraft. However, to fully control an airplane you need at least four, and a helicopter - five channels. For aircraft, two two-axis joysticks provide control functions for the elevator, direction, ailerons and engine throttle. The specific layout of functions for joysticks is of two types: Mode 1 - elevator on the left vertically and rudder horizontally, gas on the right vertically and roll horizontally; Mode 2 - gas on the left vertically and rudder horizontally, elevator on the right vertically and roll horizontally. There are also Mode 3 and 4, but they are not very common.
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Mode 1 is also called the two-handed version, and Mode 2 is called the one-handed version. These names follow from the fact that in the latter version you can control the plane for quite a long time with one hand, holding a can of beer in the other. Modellers' debate about the advantages of one scheme or another has not subsided for many years. For the authors, these disputes are reminiscent of the debate about the advantages of blondes over brunettes. In any case, most transmitters can easily be switched from one layout to another.
To effectively control a helicopter, you already need five channels (not counting the channel for controlling the sensitivity of the gyroscope). Here there is a combination of two functions per direction of the joystick (we will look at how this happens later). The handle layouts are in many ways similar to airplane ones. Among the features is the throttle stick, which some pilots invert (minimum throttle is at the top, maximum throttle is at the bottom), as they find it more convenient.
Above, we considered the minimum required number of channels to control the movement of models. But there can be a lot of functions for managing models. Especially on replica models. On airplanes, this can be control of landing gear retraction, flaps and other wing mechanization, side lights, and landing gear wheel brakes. Model copies of ships that imitate various mechanisms of real ships have even more functions. Gliders use control of flaperons and air brakes (interceptors), retractable landing gear and other functions. Helicopters also use control of gyroscope sensitivity, retractable landing gear and other additional functions. To control all these functions, transmitters are available with a number of channels of 6, 7, 8 and up to 12. In addition, modular transmitters have the ability to increase the number of channels.
It should be noted here that control channels are of two types - proportional and discrete. The easiest way to explain this is in a car: gas is a proportional channel, and headlights are discrete. Currently, discrete channels are used only to control auxiliary functions: turning on the headlights, releasing the landing gear. All main control functions are carried out through proportional channels. In this case, the amount of steering wheel deflection on the model is proportional to the amount of joystick deflection on the transmitter. So, in modular transmitters it is possible to expand the number of both proportional and discrete channels. We will look at how this is done technically later.
There is one fundamental ergonomic problem associated with multichannel. A person has only two hands, which can control only four functions at a time. On real airplanes, pilots' feet (pedals) are also used. Modelers have not yet come to this conclusion. Therefore, the remaining channels are controlled from individual toggle switches for discrete channels or knobs for proportional ones, or these auxiliary functions are obtained by calculation from the main ones. In addition, the model control signals may also not be directly controlled from the joysticks, but undergo pre-processing.
After reading the previous chapters, we hope you were able to understand two main points:
Now that we have a preliminary understanding, let's look at a few more practical points that transmitters implement:
Trimming is a very important thing. If you release the transmitter handles while driving the model, the springs will return them to the neutral position. It is quite logical to expect that the model will move straight. However, in practice this is not always the case. There are many reasons for this. For example, if you are launching a newly built aircraft, then you may incorrectly take into account the torque from the engine, and in general the model is rarely perfectly symmetrical and correct in shape. As a result, even if the rudders appear to be level, the model will still not fly straight, but in some other way. To correct the situation, the position of the steering wheels will need to be adjusted. But it is quite clear that doing this directly on the model during launches is very impractical. It would be much easier to slightly move the transmitter handles in the desired directions. This is exactly why trimmers were invented! These are small additional levers on the sides of the joysticks that set their displacement. Now, if you need to adjust the neutral position of the rudders on the model, you just need to use the desired trimmer. Moreover, what is especially valuable is that trimming can be carried out right on the go, during launches, observing the reaction of the model. If you find that initially the model does not need trimming, consider yourself very lucky.
Adjusting the sensitivity of the knob is a completely understandable function. When you set up controls for a specific model, you need to set the sensitivity so that the controls are most comfortable for you. Otherwise, the model will respond to the transmitter knobs too sharply or, on the contrary, too sluggishly. More “advanced” models allow you to set an exponential sensitivity function for the transmitter knobs in order to more accurately “steer” with slight deviations.
If we now think back to the model, we will find that depending on how the steering gears are installed and how the linkages are connected, we may need to change their direction of operation. To achieve this, all transmitters allow independent reversal of control channels.
The mechanics of the model itself may have limitations, so sometimes it is necessary to limit the stroke of the steering gears. To achieve this, many transmitters have a separate travel limitation function, although if it is missing, you can try to get by by adjusting the sensitivity of the knobs.
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Now it's time to touch on more complex aspects and tell you what mixing is.
Sometimes it may be necessary for the steering wheel on a model to be controlled simultaneously from several transmitter handles. A good example is a flying wing, where both ailerons control the height and roll of the model, i.e. the movement of each depends on the movement of the altitude stick and roll stick on the transmitter. Such ailerons are called elevons:
When we control the height, both elevons deflect simultaneously up or down, and when we control the roll, the elevons work in antiphase.
The elevon signals are calculated as a half-sum and half-difference of the altitude and roll signals:
Elevon1 = (height + roll) / 2
Elevon2 = (height - roll) / 2
Those. The signals from the two control channels are mixed and then transmitted to the two execution channels. Such calculations, which involve input from multiple control knobs, are called mixing.
Mixing can be implemented both in the transmitter and on the model. And the implementation itself can be either electronic or mechanical.
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Especially for beginners (with the exception of helicopter pilots), I would like to note that the models you will start with will most likely not require mixers for their operation. Moreover, you may not need mixers for very long (or maybe you will never need them at all). So if you decide to buy yourself a simple 4-channel joystick equipment, or 2-channel pistol equipment, then you shouldn’t be upset about the missing mixers.
You'll find a ton of other features in good transmitters in the upper price range. The extent to which they are needed for a particular model is a debatable issue. To get an idea about them, you can read the descriptions of such transmitters on the manufacturers’ websites.
To understand the difference between analog and computer transmitters, let's look at a more realistic example. About fifteen years ago, programmable phones began to spread. They differed from the usual ones in that, in addition to conversation and identifying the number of the calling subscriber, they made it possible to program one button to dial an entire number, or create a “black list” of subscribers to whose calls the phone did not respond. A bunch of additional services appeared that the average subscriber often did not need. So, an analog transmitter is like a simple telephone. It usually has no more than 6 channels. As a rule, the simplest of the services described above are implemented: there is channel reversal (sometimes not all), trimming and sensitivity adjustment (usually for the first 4 channels), setting the extreme values of the gas channel (idle speed and maximum speed). Adjustments are made using switches and potentiometers, sometimes using a small screwdriver. Such devices are easy to learn, but their operational flexibility is limited.
Computer equipment is characterized by the fact that all settings can be programmed using buttons and a display in the same way as on programmable phones. There can be a lot of services here. The main ones worth noting are the following:
The number of functions and price of computer equipment varies quite widely. It’s best to always look at the manufacturer’s website or instructions for specific features.
The cheapest devices may come with a minimum of functions and are focused primarily on ease of use. These are primarily model memory, digital trimmers and a couple of mixers.
More complex transmitters, as a rule, differ in the number of functions, an expanded display and additional data encoding modes (to protect against interference and increase the speed of information transfer).
Top models of computer transmitters have large-area graphic displays, in some cases even with touch controls:
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It makes sense to buy such models for ease of use or for some particularly tricky functions (which may only be needed if you want to seriously engage in sports). Sophistication leads to the fact that top models already compete with each other not in the number of functions, but in ease of programming.
Many computer transmitters have replaceable model settings memory modules that allow you to expand the built-in memory and also easily transfer model settings from one transmitter to another. A number of models provide for changing the control program by replacing a special board inside the transmitter. In this case, you can change not only the language of menu prompts (Russian, by the way, the authors have not encountered), but also install more recent software with new capabilities in the transmitter.
It should be noted that flexibility in the use of computer equipment also has negative features. One of the authors recently gave his mother-in-law a programmable phone, so she tinkered with programming it for a week and returned it with a request to buy her a simple, as she says, “normal phone.”
Now we will move away from the problems of modeling and consider issues of radio engineering, namely, how information from the transmitter gets to the receiver. For those who do not really understand what a radio signal is, you can skip this chapter, paying attention only to the important recommendations given at the end.
So, the basics of model radio engineering. In order for the radio signal emitted by the transmitter to carry useful information, it undergoes modulation. That is, the control signal changes the parameters of the radio frequency carrier. In practice, control of the amplitude and frequency of the carrier, denoted by the letters AM (Amplitude Modulation) and FM (Frequency Modulation), has been used. Radio control uses only discrete two-level modulation. In the AM version, the carrier has either a maximum or zero level. In the FM version, a signal of constant amplitude is emitted, either with a frequency F, or with a slightly shifted frequency F + df. The FM transmitter signal resembles the sum of two signals from two AM transmitters operating in antiphase at frequencies F and F +df, respectively. From this it can be understood, even without delving into the intricacies of radio signal processing in the receiver, that under the same interference conditions, an FM signal has fundamentally greater noise immunity than an AM signal. AM equipment is usually cheaper, but the difference is not very large. Currently, the use of AM equipment is justified only in cases where the distance to the model is relatively small. As a rule, this is true for car models, ship models and indoor aircraft models. In general, you can fly using AM equipment only with great caution and away from industrial centers. Accidents are too expensive.
Modulation, as we have established, allows useful information to be superimposed on the emitted carrier. However, radio control uses only multi-channel information transmission. To do this, all channels are compressed into one through coding. Currently, only pulse-width modulation, denoted by the letters PPM (Pulse Phase Modulation) and pulse-code modulation, denoted by the letters PCM (Pulse Code Modulation), are used for this. Due to the fact that the word "modulation" is used to refer to coding in multi-channel radio control and to superimpose information on the carrier, these concepts are often confused. Now it should become clear to you that these are “two big differences,” as they like to say in Odessa.
Let's consider a typical PPM signal of five-channel equipment:
The PPM signal has a fixed period length T=20ms. This means that information about the positions of the control knobs on the transmitter reaches the model 50 times per second, which determines the speed of the control equipment. As a rule, this is enough, since the pilot’s reaction speed to the model’s behavior is much slower. All channels are numbered and transmitted in numerical order. The value of the signal in the channel is determined by the time interval between the first and second pulse - for the first channel, between the second and third - for the second channel, etc.
The range of changes in the time interval when moving the joystick from one extreme position to another is defined from 1 to 2 ms. A value of 1.5 ms corresponds to the middle (neutral) position of the joystick (control stick). The duration of the interchannel pulse is about 0.3 ms. This PPM signal structure is standard for all manufacturers of RC equipment. The average handle position may differ slightly from one manufacturer to another: 1.52 ms - for Futaba, 1.5ms - y Hitec and , 1.6 - y Multiplex. The range of variation for some types of computer transmitters can be wider, reaching from 0.8 ms to 2.2 ms. However, such variations allow the mixed use of hardware components from different manufacturers operating in PPM encoding mode.
As an alternative to PPM coding, PCM coding was developed about 15 years ago. Unfortunately, various manufacturers of RC equipment could not agree on a single format for the PCM signal, and each manufacturer came up with their own. More details about the specific formats of PCM signals from equipment from different companies are described in the article " PPM or PCM?". The advantages and disadvantages of PCM coding are also given there. Here we will only mention the consequence of different formats: in PCM mode, only receivers and transmitters from the same manufacturer can be used together.
A few words about the designations of modulation modes. Combinations of two types of carrier modulation and two coding methods give rise to three options for equipment modes. Three because amplitude modulation is not used together with pulse-code modulation - there is no point. The first has too poor noise immunity, which is the main purpose of using pulse-code modulation. These three combinations are often referred to as: AM, FM and PCM. It is clear that in AM there is amplitude modulation and PPM coding, in FM there is frequency modulation and PPM coding, and in PCM there is frequency modulation and PPM coding.
So now you know that:
Modular transmitters are produced mainly in remote control versions. In this case, there is a lot of space on the remote control panel where you can place additional knobs, toggle switches and other controls. Among other cases, we will mention a module for controlling a twin-engine boat or tank. It is installed instead of a two-axis joystick and is very similar to the clutch levers of a crawler tractor. With its help you can deploy the following models on a patch:
Now we will explain how channels are compacted with a modular expansion of their number. Different manufacturers produce modules that allow up to 8 proportional or discrete additional channels to be transmitted over one main channel. In this case, an encoder module with eight knobs or toggle switches is installed in the transmitter, occupying one of the main channels, and a decoder with eight proportional or discrete outputs is connected to the receiver in the slot of this channel. The principle of compaction comes down to sequential transmission through this main channel of one additional channel in every 20 millisecond cycle. That is, information about all eight additional channels from the transmitter to the receiver will reach only after eight signal cycles - in 0.16 seconds. For each decompressed channel, the decoder produces an output signal as usual - once every 0.02 seconds, repeating the same value eight times. From this it can be seen that compacted channels have much lower speed and are inappropriate to use to control fast and important control functions of the model. In this way, you can create 30-channel equipment sets. What is this for? As an example, here is a list of functions of the lighting and signaling module of a copy of a mainline tractor:
Modular transmitters are more often used by copyists, for whom the spectacular behavior of the model, the realism of how it looks, and not its dynamics of behavior are more important. A large number of different modules for specific purposes are produced for modular transmitters. We will only mention here the aileron trimming unit for aerobatic models. Unlike monoblock transmitters, where control parameters in the “flaperon” modes, the air brake (in our opinion “crocodile”, and in the West “butterfly”) and differential deviation are programmed in the menu, here each parameter is displayed on its own knob. This allows you to make adjustments directly in the air, i.e. without taking his eyes off the flying model. Although this is also a matter of taste.
The radio control equipment transmitter consists of a housing, controls (joysticks, knobs, toggle switches, etc.), an encoder board, an RF module, an antenna and a battery. In addition, the computer transmitter has a display and programming buttons. Explanations on the body and controls were given above.
The encoder board contains the entire low-frequency circuit of the transmitter. The encoder sequentially polls the position of the controls (joysticks, knobs, toggle switches, etc.) and, in accordance with it, generates channel pulses of the PPM (or PCM) signal. All mixing and other services (exponent, stroke limitation, etc.) are also calculated here. From the encoder, the signal goes to the RF module and the trainer connector (if there is one).
The RF module contains the high-frequency part of the transmitter. It contains a master quartz oscillator that determines the channel frequency, a frequency or amplitude modulator, an amplifier-output stage of the transmitter, a matching circuit with the antenna and filtering out-of-band emissions. In simple transmitters, the RF module is assembled on a separate printed circuit board and placed inside the transmitter housing. In more advanced models, the RF module is housed in a separate housing and is inserted into a niche on the transmitter:
In this case, there is no replaceable quartz, and the radio signal carrier is formed by a special frequency synthesizer. The frequency (channel) at which the transmitter will operate is set using switches on the RF unit. Some top transmitter models can set the synthesizer frequency directly from the programming menu. Such capabilities make it possible to easily distribute pilots to different channels in any combination of races and rounds of competition.
Almost all radio control transmitters use a telescopic antenna. When unfolded it is quite effective, and when folded it is compact. In some cases, it is possible to replace the standard antenna with a shortened helical antenna, produced by many companies, or with a homemade one.
It is much more convenient to use and more durable in the hustle and bustle of competition. However, due to the laws of radio physics, its efficiency is always lower than that of a standard telescopic one, and it is not recommended for use for flying models in complex interference environments in large cities.
During use, the telescopic antenna must be extended to its full length, otherwise the communication range and reliability drop sharply. With the antenna folded, before flights (races), the reliability of the radio channel is checked - the equipment should work at a distance of up to 25-30 meters. Folding the antenna usually does not damage the operating transmitter. In practice, there have been isolated cases of the RF module failing when folding the antenna. Apparently, they were caused by low-quality components and could have happened with the same probability regardless of the folding of the antenna. And yet, the telescopic antenna of the transmitter does not radiate the signal well in the direction of its axis. Therefore, try not to point the antenna at the model. Especially if it is far away and the interference environment is bad.
Most even simple transmitters have a “trainer-student” function, which allows a novice pilot to be trained by a more experienced one. To do this, two transmitters are connected with a cable through a special “trainer” connector. The trainer's transmitter is switched on to the radio signal emission mode. The student's transmitter does not emit a radio signal, but the PPM signal from his encoder is transmitted via cable to the trainer's transmitter. The latter has a “trainer-student” switch. In the “trainer” position, a signal about the position of the trainer transmitter handles is transmitted to the model. In the "student" position - from the student transmitter. Since the switch is in the hands of the trainer, he takes over control of the model at any moment and thereby protects the beginner, preventing him from “making wood.” This is how flying model pilots are taught. The trainer connector contains the output of the encoder, the input of the trainer-student switch, ground, and the power control contacts of the encoder and the RF module. On some models, connecting the cable turns on the encoder's power while the transmitter's power is off. In others, shorting the control contact to ground turns off the RF module when the transmitter power is turned on. In addition to the main function, the trainer connector is used to connect the transmitter to a computer when used with a simulator.
The power supply for the transmitters is standardized and is supplied from a nickel-cadmium (or NiMH) battery with a nominal voltage of 9.6 volts, i.e. from eight cans. The battery compartment in different transmitters has different sizes, which means that the finished battery from one transmitter may not fit another in size.
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The simplest transmitters can use ordinary disposable batteries. For regular use this is ruinous.
Top models of transmitters may have additional components useful to the modeler. Multiplex, for example, in its 4000 model integrates a panoramic scanning receiver, which allows you to see the presence of emissions in the frequency range before flights. Some transmitters have a built-in (with remote sensor) tachometer. There are options for a coaching cable made on the basis of optical fiber, which galvanically decouples the transmitters and does not create interference. There are even means of wirelessly connecting a trainer with a student. Many computer transmitters have replaceable memory modules that store information about the model settings. They allow you to expand the set of programmed models and transfer them from transmitter to transmitter.
So now you know that:
After reading a brief introduction to the topic of radio control equipment transmitters, you have a rough idea of what type of transmitter you need. However, the variety of market offers does not make the problem of choice easier, especially at the beginning of radio modeling. Let us give you some advice on this matter.
The radio control transmitter is the most enduring part of all things modeling. It is in the hands of the pilot, and does not rush around at terrible speed, trying to injure those around him and the model itself with all its contents. If you do not reverse the polarity of the transmitter battery, do not step on it or drop it on the floor, then it can faithfully serve for years and decades. If you are engaged in modeling not alone, but together with a close friend, you can generally purchase one transmitter for two. Since the transmitter is a durable component, it is better to purchase a good device right away. It won't be cheap, but it will cover your growing needs over time, and you won't have to sell it a year later for half the price because it's missing any mixers or other features. But you shouldn’t go to extremes and immediately buy a device in the upper price range. The transmitters for champion athletes contain capabilities that will take years to understand and use. Think about whether you need to pay extra money for prestige.
According to the authors' experience, the quality of transmitters depends on their price group. Apparently, at manufacturing plants, more expensive models are more strictly controlled both during assembly and at the stage of purchasing components. Unprovoked transmitter failure is generally an extremely rare thing, and almost never occurs in expensive models.
For expensive transmitters, special aluminum cases are produced that are used for storage and transportation to the airfield. For cheaper devices, you can purchase a special plastic box, or make it yourself. Such special packaging should not be neglected by those who regularly (weekly) go on flights or races. It will more than once save your favorite transmitter from shock and destruction, which has served you for many years and may be inherited by your son.
