ShortSnorter
Well Known Member
I had an interesting experience this afternoon when I was doing some ground testing of a standard install G3X AP system. After I got home I did some "VAF'ing" to see what others experience has been and ran across this thread. Post #33 was exactly the scenario I was testing.
To be as brief as possible what I was doing was verifying that the torque on the GSA 28 was low enough I could over power. Previously I had done the directional control tests ensuring the wiring was correct, but had never done the "over power test." To my surprise, when I tested the right aileron up movement force (trying to over power with left stick), I heard a THUNK. At that point I had no left aileron (jammed controls) but could move center to right freely. I knew the only thing it could be was some sort of linkage issue so I pulled the inspection panel and found the first picture below. I couldn't for the life of me figure out how it went over center as I had check control stops and verified with the servo arm travel positions.
I was able to move the arm back from the over center position and verify the mechanical control stops and the the corresponding position of the servo arm (2nd picture). I'm not sure how, but my theory of what happened was as it reached it maximum limit, the servo arm was JUST far enough to allow it it pivot over center with enough force. I verified this by manipulating the servo arm by hand and pivoted past the mechanical stop to the over center position (1st picture).
(3rd Picture) I moved the push rod linkage to the center hole (from the hole nearest the shaft) and due to the changed geometry, was unable to replicate the over center position by hand or with AP servos active. I am definitely planning on installing the mechanical stops that came with the servo! The only reason I did not install was the instructions say as long as the geometry does not allow over center then the stops were optional.
Please go check your AP Servos!!! Even though though they check out visually through full range of motion you could have a situation like mine. I doubt there would ever be a real world scenario of full AP commanded aileron deflection that could potentially cause this scenario, but its worth a piece of mind to check it out.
**Not sure why the pics are turned?!
To be as brief as possible what I was doing was verifying that the torque on the GSA 28 was low enough I could over power. Previously I had done the directional control tests ensuring the wiring was correct, but had never done the "over power test." To my surprise, when I tested the right aileron up movement force (trying to over power with left stick), I heard a THUNK. At that point I had no left aileron (jammed controls) but could move center to right freely. I knew the only thing it could be was some sort of linkage issue so I pulled the inspection panel and found the first picture below. I couldn't for the life of me figure out how it went over center as I had check control stops and verified with the servo arm travel positions.
I was able to move the arm back from the over center position and verify the mechanical control stops and the the corresponding position of the servo arm (2nd picture). I'm not sure how, but my theory of what happened was as it reached it maximum limit, the servo arm was JUST far enough to allow it it pivot over center with enough force. I verified this by manipulating the servo arm by hand and pivoted past the mechanical stop to the over center position (1st picture).
(3rd Picture) I moved the push rod linkage to the center hole (from the hole nearest the shaft) and due to the changed geometry, was unable to replicate the over center position by hand or with AP servos active. I am definitely planning on installing the mechanical stops that came with the servo! The only reason I did not install was the instructions say as long as the geometry does not allow over center then the stops were optional.
Please go check your AP Servos!!! Even though though they check out visually through full range of motion you could have a situation like mine. I doubt there would ever be a real world scenario of full AP commanded aileron deflection that could potentially cause this scenario, but its worth a piece of mind to check it out.
**Not sure why the pics are turned?!
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