ArduPilot Servo Trim & Reverse not working

Hi - very new to this. I have built a 6 wheeled rover.

I have a Cuav x7+ controlled by H16 ground station.

Motor controller is sabretooth Sabertooth Dual 12A 6V-24V.

2 servos for tilt pan Fpv camera.

Im using latest ardu rover firmware.

I cannot seem to reverse, or change trim for the servos, and it appears it can’t be done at the transmitter either. (talking with cuav) I know I can get a reversing cable. But surely there is a way to adjust trim at a bit of a loss any advice would be appreciated.


Did you try SERVOx_REVERSED and SERVOx_TRIM parameters? They are in the parameter list and all channels have them individually.

Yes tried many times… Don’t appear to have any affect. I’m not sure if I’m missing a step. But I make the change. Restart the FC… And nothing changes.

Just to be clear, you stated very new to ArduPilot.
When you change a parameter, it should appear as green background.
Click write params, and then, refresh params.
The green background will disappear on this parameter.
Make sure the value of the parameter is changed.
I updated my comment.
“SERVOx…” parameters are for output channels (servos).
“RCx…” parameters for input channels (receiver).

Thanks for checking - yes I write parameters, see them green. I see the changed values.

Are you saying that if I wanted to reverse a servo, I need to do that in more than one place?

Typically I have tried the radio calibration screen, tick box… Servo screen… Tick box… As well as parameters. I wonder if I’m getting mixed up here.

Radio calibration and servo output screens are designed just for convenience.
They change and save parameters in the parameter list.
Also, for example when you counter turn the potentiometer clock-wise, and see the PWM value on the radio calibration screen is decreasing, probably it is reversed on your transmitter. You can reverse it from the transmitter or from the autopilot.
By design choice pulling the sticks to right or up should increase the PWM on the input channels.
Also pulling the sticks to left or down should decrease the PWM on the input channels.
Probably these will be OK on default parameters and default model on the transmitter.
I explained them just in case.
If they behave just as is, but you want an undesired servo movement, then you can change “SERVOx” parameters.

For now, don’t change anything related with “RCx” parameters (radio calibration screen) yet. If some of them reversed, make them 0 (in parameters list).
Just the radio calibration is fine.
Change one parameter at a time to find out what is changed.
For example, if you assign a camera to a potentiometer and camera turns right when you decrease the potentiometer (turning counter-clockwise), to reverse the camera servo movement, change the related SERVOx_REVERSED parameter.
Above infos are for all ArduPilot vehicles, I am working more on the Copter and Plane rather than Rover, but most of the functionalities is same when configuring inputs/outputs.
Hope this helps and clarify some things.

Thanks for your time explaining, I’ll give it another good run through and see if I’ve missed something. Will report back in any case.

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Hi there, getting back to this… Was on leave for a few days. :blush:. I’m confident I know how to change the parameters… as per your explanation…that is exactly how I have done it in the past…however I can confirm, none of the servo outputs make any change for me.

Reporting back this has been solved via transmitter settings. I did not get further with autopilot settings.

The supplier provided me with a password to get into advanced parameters of the H16, where I could reverse the servo signals.

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