In this article, we will look at the procedure for installing the radio system of an rc helicopter.

Before proceeding to install your radio system, you will need to do some tests to ensure that it will function properly in the rc heli. The range test should be performed according to your radio manufacturers instructions, but here is a general procedure.

1. Ensure that both the transmitter and receiver batteries are fully charged.
2. With only the battery and servos connected to the receiver, turn both the transmitter and receiver on.
3. Collapse the transmitter antenna .
4. Walk away from the receiver, while moving the transmitter sticks.
5. Continue walking until the servo movements become erratic.
6. Walk back towards the receiver, and stop when control returns to normal.
7. Compare this distance with the specified minimum range check distance in your owners manual.

If the distance you found is less than the specified distance in your manual, then the radio is not safe to use in your model and will have to be sent back to the manufacturer for repair.

Before mounting the servos in your rc helicopter, ensure that the throws are at 100%, and that the servo arms are set perpendicular to the servo body. Also, center all the trims and make sure that the batteries in both the receiver and transmitter are fully charged. This is important because all adjustments you will be making require the radio to be on. When you are about to attach the servos to the fuselage, disconnect the battery and servos from the receiver. It is important that only the rubber grommets supplied with your servos touch the rc helicopter body, and that the mounting screws are tight enough to compress the grommets. Do not tighten the screws too much, or the grommets can become too compressed to much to be effective shock absorbers. Once the servos are installed in the fuselage, reconnect the battery and receiver. After double checking that the all the trims are set to neutral and that the servo arms are mounted properly, you can proceed with installing the ball links onto the inner holes of all the servos.

The rc helicopter should come with pre-cut pushrods. Install these on the servo arms by either screwing on the ball links, or using snap on clevises. If you are using the snap on clevises, be sure to secure them by sliding on a piece of fuel tubing. This will prevent them from coming loose in flight. Once the aileron linkage is connected, move it with your hands to see if the swashplate moves freely, without friction. Install the other linkages in the same way, but be careful to match the throw of the throttle servo to the carburetors range of travel. If this is not done properly, it can cause overheating and damage the engine. Also, be sure that an idle position on the transmitter does not turn off the engine completely. There still needs to be a way to turn off the engine, but this can be accomplished with the throttle trim tabs on the transmitter.

The gyroscope should be installed as shown in the owners manual. Make sure to place it where it is unlikely to be damaged. Most rc helicopters will have a specified location for the gyro. Use servo mounting tape to attach the servo, this will insulate it against vibration and attach it firmly to the fuselage.

Mount the on/off switch on the side of the rc helicopter opposite the exhaust. Also, mount the switch in a place where it will be easy to access. Orient it in a logical way, so that you will not turn it off accidentally.

The receiver and battery are now ready to be mounted. Before proceeding, cover both with plastic wrap to protect against fuel, dirt, and other contaminates. Pack them with rubber foam, and secure them with rubber bands. Depending on the type of antenna your radio system has (wire or whip), the antenna will have to be either routed outside the helicopter, or left inside the canopy. Be sure to follow the instructions in your owners manual, and don’t wrap the antenna around itself. This will reduce it’s range and could lead to a crash.

In addition to using the tips above to help you install your radio system, always read the user manual of both your rc helicopter and your radio system.

If you have purchased an rc helicopter in kit form, you will then need to get a radio for it. The radio system is responsible for sending control signals to your rc helicopter. When you move the sticks on the transmitter the motion is converted to signals and sent out by the transmitter, picked up by the receiver, and relayed to the servos which control the flight of the rc helicopter. There are several types of radios available, and each has different benefits and costs.

A common question is whether or not an rc airplane radio can be used in with an rc helicopter. The answer is yes, but you will have less control options than you would when using an actual rc helicopter radio.

An rc helicopter radio is different from an airplane radio in several ways. The most important is the throttle for an rc airplane is used to control the engine speed, not the collective pitch. In an rc helicopter, both must be controlled. In order to use this kind of radio with an rc helicopter, both the engine throttle and collective pitch servos must be linked together via a Y harness. This will work, but you will have less control than if the pitch and throttle servos were independent of each other. Using this type of system works best in fixed pitch rc helicopters, because they do not use the collective pitch control in the first place.

When shopping for an rc helicopter radio, you will come across the term “channel” often. It has two different meanings, and each is important in your buying decision. It can mean either the number of servos the radio can control (which relates to the number of degrees of freedom the rc helicopter can have), or the specific frequency subset that the radio signal is sent on (the 72MHz frequency band is divided into channels numbered 11 to 90). A two channel radio can control two servos (for example the throttle and rudder servos). A three channel radio could have both throttle and rudder control, as well as elevator control. A rc helicopter will need at least 4 channels, and typically 5 or 6 channels. Some radios have many more channels, but these are not important to the beginner. The basic 5 channels control:

1. Aileron
2. Elevator
3. Throttle
4. Collective pitch
5. Rudder

The extra channel can be used to control gyro sensitivity or other functions. The cost of a radio system is highly dependent on the number of channels available. When buying your first rc helicopter radio, try to get one with at least 5 channels. More channels will enable you to use more advance features as you progress in the hobby.

Radio systems can also use different methods to transmit their signals. These can be FM, PCM, or PPM, or spread spectrum. The most basic is FM, or frequency modulation. This method is the same type used by FM radio stations, but on a different frequency. Many FM radios can operate simultaneously as long as they are on different frequencies or different channels on the same frequency. If two radios are operating on the same frequency and the same channel, interference will results and one or both of the models flying can crash.

PPM (or pulse proportional mode) radios are better than a normal FM radios because they can operate servos at a higher resolution. The radio transmits by first sending a timing pulse, and following this with the actual command information. The advantage of this system is that the receiver knows what to expect before the command arrives. A different timing pulse is sent for each control channel, and this cycle repeats many times per second. The rate at which these pulses occur is called the pulse rate of the radio. A greater pulse rate gives better control, but getting a high pulse rate radio is not so important for the beginner or casual flyer.

PCM (or pulse code modulation) is similar to PPM except that each pulse is coded. The rc helicopter will only respond to signals with this specific code. This means that it will cope better to interference. Although this technology is helpful, it does not make the rc helicopter immune to all interference. If another pilot turns on a radio using the same frequency and channel, the rc helicopter can still have its signals washed out by the other transmitter and crash.

A synthesized radio lets the pilot transmit on different frequencies. This is helpful when you are flying at a club where there are many other pilots, because you do not have to change the crystal in the transmitter and the receiver to change channels.

The most recent radio technology eliminates the need for channel frequency control, and is immune to almost all forms of interference. Spread spectrum radios can transmit and receive on multiple channels, at a frequency of 2.4 Ghz (2.4 billion cycles per second). This kind of radio automatically scans for two free channels when is is turned on. When it finds them, it uses both to transmit and receive. Spread spectrum technology is becoming more popular, and it will eventually replace the other three kinds of radios mentioned above.

Besides the type of radio, you will have to consider different types of servos to use in your rc helicopter. There are many different types, the broadest categories being: standard, coreless, and digital. Standard servos are the least expensive, but they also provide the least performance. Since the motors they use have coils wound on a rotating iron core placed between stationary magnets, they will not be able to start and stop as quickly as the coreless variety. These servos should really only be used to control the throttle of the rc helicopter. Coreless servos are the same, except that the motor inside them has coils that are rigid and rotate around a stationary magnet without requiring an iron core, and are able to accelerate more quickly. These servos typically have better resolution and more torque than their cored counterparts. Digital servos use a digital amplifier to achieve even better resolution and accuracy. Digital servos can be cored or coreless are better than non-digital servos for several reasons, including:

• More accuracy
• Faster control response
• Greater torque

These are the best type of servo, but they may not be in within the budget of the beginner. Whatever type of servo you choose, make sure that it has ball bearings supporting the output shaft. This will result in both smoother operation, and longer servo life.

Be aware that most radios come with only four servos, and you will have to buy a fifth yourself.

The last major radio component is the battery. The battery is used to power the various radio components. Most batteries are of the four cell variety, and supply 4.8 volts. This is sufficient for most models, but a 5 cell pack producing 6 volts can be useful. The more voltage you have available, the faster the servos will respond. For your first model, you should consult the instructions that came with it to determine what type of battery pack to use.

Several other radio features include, but are not limited to:

Tail rotor compensation:

Tail rotor compensation keeps the nose of the rc helicopter pointed in the same direction. This is accomplished via a gyroscope (which is explained in a previous article, ‘Introduction to RC Helicopter Gyros, Rate & Heading Hold’) telling the tail rotor how fast it needs to spin. When the pilot adjusts the pitch or throttle of the rc helicopter, the torque from the blades causes the nose to move in the opposite direction, and thrust from the tail rotor is required to counteract this.

Exponential:

Exponential allows the pilot to control how sensitive servos are. With this feature we can tell the servos how much to move for a given amount of stick movement on the transmitter. This can allow smoother control for small movements, and sharper control for large movements of the transmitter stick.

Gyro gain:

With this feature the pilot can control the sensitivity of the gyroscope on board the rc helicopter. This feature can allow for more stable flight, or easier aerobatics depending on the setting.

Electronic digital trim:

Trim can be used to correct undesired motions of a rc helicopter. It controls the adjustments of various servos during flight. For example, if I were flying a model with a slight left bank, I would slide the aileron trim lever in the opposite direction, to apply a right correction. These would cancel each other out, resulting in straight flight.

Programmable switches:

These are various extra switches located on the transmitter that enable the pilot to control special functions.

Multiple model configuration / switches:

This feature will let the transmitter control multiple models by storing the different settings for each. This is a good feature to have, because you can use one transmitter for several models, no matter how different they are. A memory feature will allow the transmitter to store this information.

Servo endpoint:

An adjustable servo endpoint will allow adjustments to the maximum throw of servos. This can be used as trim to compensate for undesired motions, by reducing the travel in the opposite direction.

Condition / flight mode:

This feature will allow different adjustments to flight parameters for different flight modes. This increases performance in all phases of flight, and is a very good feature to have.

When buying your radio, carefully consider all of the above features. If you’re unsure about your choice, you can ask more experienced pilots for help. If you take good care of your radio, it should last you many years.