What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

G3X Trim Question

lr172

Well Known Member
I notice that the AP servo provide some type of pass through for trim functions. It seems clear that the GSA 28 servo will provide auto trim in AP mode using this function. I further deduce that I can also run my manual trim through the input. My question is, do I need to pass the trim motor's required current into the AP servo trim input or is this a control level input with the servo providing the current necessary to drive the trim motor.

Also, I do not plan to use the Garmin trim mixer and will only have one trim input. Does this work without Garmin's optional trim mixer module? Also, does the G3X provide adjustment of trim speed, based upon airspeed in the standard configuration?

Thanks,

Larry
 
I notice that the AP servo provide some type of pass through for trim functions. It seems clear that the GSA 28 servo will provide auto trim in AP mode using this function. I further deduce that I can also run my manual trim through the input. My question is, do I need to pass the trim motor's required current into the AP servo trim input or is this a control level input with the servo providing the current necessary to drive the trim motor.

Also, I do not plan to use the Garmin trim mixer and will only have one trim input. Does this work without Garmin's optional trim mixer module? Also, does the G3X provide adjustment of trim speed, based upon airspeed in the standard configuration?

Thanks,

Larry

Hello Larry,

As described below, the G3X autopilot provides 3 modes of trim operation. It is only in the first mode with the servos powered off that the power to drive the trim motors does not come strictly from the GSA 28 servo, but you will want to wire your plane to provide trim motor power so you may operate your trim manually, at all times, even when the servos are powered off.

Servos Powered Down (backup trim mode)
In this dirt simple backup mode a relay closes inside the GSA 28 servo and passes the trim motor wires directly through the servo. The wires connected to input pins 11,12 at the servo are directly connected to output pins 13,14.
Servos Powered Up, Autopilot Disengaged
This is the normal mode of operation when the autopilot is disengaged. The trim control inputs on pins 11,12 of the servo are read by the servo microprocessor, and speed scheduling is added by the servo to automatically drive the trim motor and vary the speed of the trim motor (using Pulse Width Modulation) to match the speed scheduling configuration.​
Servos Powered Up, Autopilot Engaged
This is the normal mode of operation when the autopilot is engaged. It is very similar to the previous mode except that the servo ignores the inputs and drives the trim motor based on out-of-trim torque sensing that it does on its own.​

Yes, you may use your own trim system connected to pins 11,12 on the servo, which normally involves taking the low level trim switch signals from the control stick(s) to control relays which provide up to 1A of trim motor power.

Let us know if you have additional questions.

Thanks,
Steve
 
Thanks for the input and this feature is really nice. I am beginning to think I made the right decision moving to the G3X for my 10 project. I will setup relays on the trim input as I would for direct trim drive

Larry
 
Back
Top