• 2 Setup your heli
  • Belt drive
  • Servo instalation
• 2 Setup your radio
  • Channel assignment
  • Pitch and throttle curve
• 2 setup your gyro
• 2 Fly your heli
• 2 Stabilize your heli

Trex assembly tips

The cyclic on the trex is very sensitive. It is best to start by using the inner holes on the aileron and elevator servo horns. For the collective linkage use the outer hole so that you can get full travel. I would also recomend 25% to 30% exponential on the elevator and aileron channels to soften control surrounding the centre stick position. Also see the section on stabilizing the trex. Next is the tail servo. First bypass the gyro and connect the tail servo direct to the receiver so as to to centre the rudder servo. Move the servo on the tailboom so that neutral position of the servo sets the tail control lever in the middle of the tailrotor shaft. The gyro and radio trim will sort out the finer tuning of the rudder.

The ESC must be connected to the throttle channel. The ESC provide power to the receiver via the throttle channel connection. Thus the same battery that powers the motor also provides power to the receiver and servos. Throttle hold is a function used to practise auto-rotations (landing your heli without engine power). This function allows you to move the collective to any setting while holding the throttle at a given position (normally no power). This function is very handy and can be used to setup servo movements and travel without motor power. It can also be used as a safe switch preventing the motor starting when you do a preflight check.

Channel assignment

Function	JR	Futaba	Hitec
Throttle	1	3
Aileron (left and right cyclic)	2	1
Elevator (forward and backward cyclic)	3	2
Rudder (Tail)	4	4
Gyro gain	5	5
Pitch (collective)	6 (Aux 1)	6

The throttle stick on a transmitter controls two functions, the throttle (engine power) and the collective pitch. The throttle curve represents the throttle setting for given stick positions while the pitch curve represents the pitch travel for a given stick position. Some transmitters have 3-point throttle and pitch curves, others 5-point curves, and expensive transmitters may even have more. It means that for 3, 5, or more different stick positions you can set the different throttle and pitch settings. This is done to keep the rotor speed of the heli as constant as posible.

The gyro should be mounted on foam tape near the rotor head to avoid excessive vibrations. Make sure that the gain and reverse functions are easily accessible. The gyro has a top and bottom and should be mounted correctly. Be carefull not to mount the gyro on its side especially if it is a square gyro. It senses rotation around the vertical axes and will not function if mounted on it's side. Plug the tail servo into the gyro and the gyro plug into the rudder channel of the receiver. If your gyro's gain is remote adjustable, that plug (usualy only one wire) should be pluged into channel 5 (Futaba and Jr). If you leave the single wire disconnected, the gain can most of the times be adjusted manually. For best results use a fast servo on the tail (0.12 sec for 60 degree turn or faster). Ensure the gyro acts in the correct direction by turning the heli around the mainshaft while looking at the tail rotor blades. On the trex you can put your finger between the tail case and the tail rotor control lever. If you turn the nose left the tail rotor control lever should move towards the tail case and pinch your finger. When the gyro is in heading hold mode (high gain setting) it is common for the tail servo to slowly move in one direction. This effect can easily be stopped using your rudder trim on the radio. Do not use Revo Mix, the gyro will sort out the tail. Although you are using a gyro it will still be necessary to steer the tail in a hover and especialy in forward flight during turns as the gyro will stop the tail performing the windmill effect.

First ensure throttle hold is turned on and check the direction of movement on all controls. If you turn left and right using aileron the swashplate should tilt left and right respectively. If you move the elvator front and back the swashplate should tilt forward and backwards respectively. Also check the direction of rudder movement. Stop any drift of the rudder using the rudder trim. Level the swashplate with aileron and elevator trim. Close the throttle and turn off throttle hold. Slowly add throttle to start the motor add throttle untill the heli becomes light on its skids. If there is any tendence to tilt or yaw, close the throttle and trim as nesecary. Repeat the process untill the heli can take-off relatively stable. If the heli rotates on the spot, the gyro should probably be reversed. Stay low so that you can land quikly when nesecary until you gain more confidence. If the tail wanders, then raise the gain setting on the gyro. If the tail wag from side to side, then adjust the gyro gain downwards. Keep the tail pointing towards you and build some time on the simulator !

As mentioned previously the cyclic sensitivity can be desensitized by using the inner servo horn positions as well as by using your radio's exponential function. Another way to stabilize the heli is to add weights to the flybar to increase the momentum and gyroscopic effect. An easy way is add two wheel collars on each side. For maximum stability move the collars to the most outer position. With your flying skills progresing you can remove one on each side, move them inwards or totally remove them for 3D flight.

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