From RC Helicopter Wiki
The transmitter is the part of the radio control system that the pilot holds in his or her hands. Manipulating the control sticks and switches causes the transmitter to send radio signals to the receiver in the model, which are then translated into control signals. Often just referred to as 'the radio'; often abbreviated in writing to 'tx'.
Most modern transmitters are known as computer or programmable transmitters. They have a large number of settings that allow the radio to be tuned to the model that it is flying. They also have a number of model memories allowing these settings to be stored, so one radio can be used to fly different helicopters – at different times, of course! The transmitters supplied with so-called ready to fly helicopters are called stock transmitters and are usually simple and offer very little in the way of adjustment. A good programmable transmitter can make a huge difference in the flying characteristics of a helicopter.
Dedicated helicopter radios have a number of features that make them more appropriate for flying helicopters, such as a 'smooth' throttle control, rather than one held in place by a ratchet. Helicopter radios can be used to fly aeroplanes, but occasionally not vice versa.
Typical radio features include:
- Servo reversing: changes the direction the servo moves, to match the control to the installation;
- Servo travel adjust: stops the servo moving too far and binding, or to reduce control sensitivity, or for reducing CCPM interaction;
- Dual rates: change the control sensitivity at the flick of a switch;
- Exponential: makes the controls less (or more!) sensitive around the neutral (center) position;
- Programmable mixes: when necessary, allows combining of controls for better flight characteristics;
- Electronic CCPM mixing: for use with CCPM helicopters, together with:
- CCPM parameters: sets the sensitivity and direction of the cyclic and collective controls on a CCPM helicopter;
- Predefined mixes: to help reduce common control interactions;
- Trim: applies a small constant offset to a control;
- Subtrim: moves a servo center point;
- Throttle hold: moves the throttle to engine idle to allow for autorotations and as a safety aid;
- Pitch and throttle curves: control how collective pitch and throttle change with control position;
- One or more switched channels, for controlling gyro gain, retractable landing gear, cameras, etc.;
- Trainer port: to join two transmitters together so a mentor can take control of the helicopter in an emergency;
- Servo monitor: aids in troubleshooting;
- Flight timer: warns you when you may be running out of fuel or battery power.
- Throttle trim: allows engine idle position to be changed.
- Hover throttle trim: trims throttle around midstick (not generally used now).
- Hover pitch trim: trims collective pitch around midstick (not generally used now).
- Pitch trim: moves entire collective pitch range by a small amount, decreasing or increasing head speed (not generally used now).
Before flying your helicopter, you should:
- Understand your site's frequency control system before switching on the transmitter.
- Switch on the transmitter before the helicopter.
- Ensure you a using the correct model memory.
- Ensure the transmitter battery voltage is good.
- Ensure that the controls move the swashplate and tail rotor correctly.
- Perform a range check if you have made changes to the installation.
- Extend the transmitter aerial fully (or on 2,4GHz transmitters, point the antenna vertically (or sideways to you if not possible to put it close to vertical)).
When you stop flying:
- Use throttle hold (if present) as a safety.
- Turn off the helicopter before the transmitter.
 See also
- A study of transmitter/ receiver latency on RunRyder.
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