MGL Avionics User Forum

My XTreme autopilot setup used to work correctly. I hadn't used the AP for quite some time due to a sheared servo screw that I finally got around to replacing. After the repair, I went through the entire setup procedure for the pitch and bank servos. After setting up the AP, I ran the preflight check routine to verify correct operation. The pitch servo check was ok, but when I ran the bank servo test, it would correctly go to full left stick, 1/2 left stick, and center. However, if 1/2 or full right stick was checked, it barely goes right of center stick and you can hear the servo hum. I verified there is no obstruction to the servo arm or control travel (the controls are light and responsive on my dual stick Zenith CH750 STOL) and even went as far as re-setting up the bank servo, locking-in the numbers generated short of full travel of the stick left and right as the manual instructs to set the AP limits.

Any ideas or suggestions on where to go from here? Does this suggest the servo is faulty?

John
N750A

It may be that you are now operating on a different sector of the servo output throw- shear screw in a hole 90 or 180 degrees from where it was.
If so the servo sense position may be traversing the 0/4096 transition and confusing the AP.
Check that from left to right you get a continuous incremental position indication with no 0/4096 jump.

Another possibility is the large output gear in the servo is not concentric or damaged in some way and is binding and stalling the srevo motor.
But given you have full smooth control travel that is unlikely.

Another possibility is that the servo/linkage is binding when the servo is driving and applying force to the system due to some misalignment or interference or whatever.
Test by moving the ailerons manually by directly manipulating the servo control horn.