Tutorials : How to set up Cross Trims

Mike Shellim 21 Dec 2001

updated 22 Jan 2002 - centre trim removed.

Cross Trims

This article shows how to change the normal action of a trim lever, so it affects a different control. In the example, the Rudder trim lever (LH stick) will be used to trim the Aileron control (RH stick).

Solution

Assign Aileron to C, and Aux 6 to trim lever TA.

Stick	Control	Remarks
C	AILERON	Aileron = rt stick
TA	AUX6	Aux 6 = left trim lever

We'll use a servomix to add the Aileron signal + the trim signal.

Mixer Schematic

Servomix "my_xtrim"

              ---------------    
              |             |
Aileron  -->  | Servomix    |
AUX6     -->  | "my_xtrim"  |--> Aileron
Servo         |             |
              ---------------

my_xtrim set up

my_xtrim
Input#	Control/Mixer	Switch	Curve	Remarks
1	AILERON	ON	-100/0/100	Aileron
2	AUX6	ON	-range/0/+range	Trim
Notes The mixer adds both inputs together i.e. Aileron + Trim. Assign the aileron servo to the mixer .

Enhancements

Add Trim Offset

A trim offset facility allows the trim lever to be brought back to the centre following flight tests. Add a third Aileron input as follows:

my_xtrim with 3rd input for "trim offset"
Input#	Control/Mixer	Switch	Curve	Remarks
1	AILERON	ON	-100/0/100	Aileron
2	AUX6	ON	-range/0/+range	Trim
3	FIXED VAL	ON	offset	Trim Offset
Notes range is the trim range. A typical value would be around 20. The curve for FIXED VAL is just a single point offset.

Encapsulate in Multimix

By using a multimix instead of a servomix, you can plug this behaviour into any servomix requiring Aileron + Trim.

Notes

The effect of the trims is NOT reduced at the end points, thus they work like standard (not centre) trims.