View Full Version : Joystick Axis interfering with Autopilot

06-19-2007, 09:45 AM
Well I have started my quest to build a generic cockpit. I am going generic at first so I can learn what it takes without concerning myself with specific panel layouts. When I introduced myself one of the replies was to find a USB joystick and basically start with that. I thought that was a good idea as I can take an axis or button and assign as needed. So I hit my first bump in the road.

I came across a used Saitek ST290 that I feel has what I need for a start. My first thing was to setup elevator trim control on the throttle axis. I did this so i could set the trim and it would stay in place. It works like a charm when hand flying the plane. The problem occurs when I try to engage the autopilot.

When i have the axis assigned to the trim the autopilot will engage but cannot control the aircraft altitude. Speed and turns work but apparently me having an axis assigned to the elevator trim prevents the AP from controlling altitude. When i remove the axis assignment the AP ALT works fine.

So where do i go from here?

Once I know what I need to solve this I will disassemble joystick to develop an actual trim wheel.

Radio controls wil be next along with radio frequency LCD displays.

Thanks for the help



06-19-2007, 07:27 PM
This is probably a long shot, but here is how the trim works in my flight deck when using the autopilot. When the A/P is controlling the airplane, the A/P actually uses the trim control (offset) to raise or lower the nose. I know that because I have trim wheels in my throttle assembly which have no real function, but which rotate anytime the trim is changed, either by the A/P or manually.

Whenever there is a change in attitude commanded by the A/P, the trim wheels rotate. So, the A/P is using the same axis (or offset) you are using in your yoke trim control and the yoke may be conflicting with the A/P.

Having said that, I also know that on a CH yoke, the trim control on the yoke also rotates the trim wheels and does not interfere with the A/P function. So, yours should work as well. Maybe, as a workaround, you can try assigning the trim axis to the elevator axis instead just to see if that is the problem. This may work for you , but this also just a wild guess on my part.


06-19-2007, 07:55 PM
Trim on a yoke/joystick is best set as 2 buttons - trim up and trim down. Thats how they are in real aircraft with electric trim on the yoke. You won't have a trim wheel you can spin but thats a compromise that has to be made it seems.

06-19-2007, 09:10 PM
the replies would be that way. I guess I will need to set it up and use it when I am flying the small GA where I do not use AP and disconnect it when I am going to fly the big birds.

Thanks for the replies. Next I am going to work on a radio stack.