Tutorials : How to Vary Combi Mix (During Flight)

Mike Shellim   13 Dec 2001

Revised 22 Jan 2002 - Multimix solution removed.
Revised 23 Jan 2003 - Added 'using a pure aileron signal'.

The mc4000 allows many parameters e.g. Differential, Exp, Travel to be set independently for each flight mode. Unfortunately this does not apply to Combi which can only be a preset value, or OFF.

This article shows a workaround, which allows the amount of combi to be varied via a flight mode (or other) switch.

Overview of solution

The solution uses a servomix instead of the built-in Combi:

Servomix "my_combi"
Aileron (T1-1) -->  |             |
Aileron (T1-2) -->  | Servomix    |
Aileron (T1-3) -->  | "MY_COMBI"  |--> Rudder Servo
       Rudder --->  |             |

There are three aileron inputs, of which only one is active. The servomix mixes the active aileron input and with the rudder signal. The output signal drives the rudder servo.

Mixer set up

Mixer set up
Input # Control/Mixer Switch  Curve
1 AILERON T1-1  -x/0/x
2 AILERON T1-2  -y/0/y
3 AILERON T1-3  -z/0/z
4 RUDDER ON -100/0/100
  • The three Aileron inputs have curves which define rates of x%, y% and z%.
  • Ensure that only one aileron input is active at any time. In this example, we assign three- position switch T1 so that one Aileron input only is active in each switch position.
  • The mixer output is equal to sum of all the inputs, i.e. the active aileron  (x%,  y% or z% depending on T1) + Rudder (100%).
  • The rudder servo is assigned to my_combi.
  • To disable combi in one position, set x, y or z to zero.


Menu/Screen Action
Assign Control Assign C = Aileron, A = Rudder
Assign Switches Assign T1 = 3-position switch
Assign Servo Assign Servo 1 = Servomix
Assign Mixer Set inputs for servomix as in table above
Servo Travel Set curves and switches for Servo 1 as in table above. Repeat for all four inputs.


For trimming purposes, have a single aileron input which is continuously variable on a slider. To do this, set one aileron input and use an analogue switch on F.

Input # Control/Mixer Switch  Curve Comment
1 AILERON A6/F -max/0/max Slider F attenuates max 
2 RUDDER ON -100/0/100