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D6 - RADIO - I have 2 servos to control the ailerons on my helicopter, but my radio only provides a setting for one of them - what goes on ?

This is a question that often confuses new pilots.

The problem originates form the fact that all RC radio systems started life out as controllers for fixed wing aircraft (planks).  Planks do not have a pitch control as such, as they do not need it.

Once helicopters came along, there was an obvious need for another controlled channel to let the pilot control the angle of the main rotor blades, at least for Collective Pitch (CP) helicopters.

So what does any CP helicopter need ?

1 - An elevator servo/channel to control the pitch of the helicopter (nose up/down)

2 - An aileron servo/channel to control the roll of the helicopter ('Wings up/down')

3 - A throttle channel to control the speed of the motor (and therefore head speed)

4 - A rudder servo/channel to control the yaw of the helicopter (Nose left/right)

5 - A gyro gain control channel to control the way the gyro operates

6 - A Pitch servo/channel to control the pitch of the main rotor blades independently of the throttle setting.

So, if we try to match these to the names the channels on a receiver (Rx) are given most often we get the following :

  • Ch 1 - Aileron

  • Ch 2 - Elevator

  • Ch 3 - Throttle

  • Ch 4 - Rudder

  • Ch 5 - Gyro control

  • Ch 6 - Aux 1

  • Ch 7 - Aux 2

  • ...........etc.........

So what works for the pitch control we so badly need ? Well, most radios provide this control on Ch 6, commonly named AUX1, or sometimes Pitch.

OK you say, fair enough, but my swash plate has 2 servos connected one to each side of the swash plate, and both are used for aileron control.  Which one goes where ?

Now it starts to get more complicated.  There are two different types of swash plate system used by RC CP helicopters. The original method was/is called "mechanical" mixing, while the other is called "electronic" mixing.  These are even known as mCCPM and eCCPM.  The mechanical mixing uses a 90 degree swash plate arrangement for the servo connections, whilst CCPM uses 120 degree connections

  

The problem is that when the radio is using CCPM (Cyclic Control Pitch Management) to "mix" the operation of all the servos that attach to the swash plate, as far as it is concerned, both of those aileron servos have to operate in OPPOSITE directions for Aileron control, but in the SAME direction for pitch control.  That is where CCPM comes in, and in most cases, it assumes that the aileron servo mounted on the left side of the helicopter is the one connected to the AILERON channel (CH 1),while the other one needs to be mounted on the right.  WARNING - This setup  is not cast in stone, and maybe the opposite way around on some helicopters.

So for CCPM systems, all you really have to remember is that the servo that is connected to the Aileron (Ch 1) will be "in charge" of aileron movement, while the servo connected to the AUX1/Pitch (Ch 6) will be working in conjunction with Ch 1 to handle AILERON and PITCH.  All swash plate servos have to work TOGETHER to achieve the required swash plate movements.

For non CCPM it is far more simple, as the AUX1/Pitch control ONLY the pitch control, which is always handled by one single servo alone, and the aileron control is handled by one other servo. In other words, each servo performs exactly one task all by itself, and does not work in conjunction with the other swash plate servos.

HOPE THIS DESCRIPTION HELPS ... ?

 

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