BillL
Well Known Member
So there I was, taking off from Airventure 2019 Wednesday morning and suddenly the ailerons did not want to work. I pushed left-right hard and it seemed to be ok. But . . then the AP had no roll control.
Back home in an hour the culprit was the servo. It locked up and sheared the screw designed for this failure mode.
Root cause: Sitting on the ground the sweltering hot and high humidity from Friday to Wednesday at OSH, there was liquid in the stepper motor. The PM rotor and stator had light corrosion and filled the air gap. I removed the motor and could not turn it with the gear held in a vice! Light sanding with some 320 sandpaper, wiped clean and it can be rotated with the slippery rotor shaft, a quite low torque to be sure.
I have never seen this type of failure posted, and since it was only this one time my plane has every been outside overnight or in the rain, I thought it was noteworthy to warn others of this possibility.
Check on the ground and don't take off like I did.
The shear screw that saved my life. Smart people at TruTrak, thanks.
Rust on the stator, rotor was the same.
Back home in an hour the culprit was the servo. It locked up and sheared the screw designed for this failure mode.
Root cause: Sitting on the ground the sweltering hot and high humidity from Friday to Wednesday at OSH, there was liquid in the stepper motor. The PM rotor and stator had light corrosion and filled the air gap. I removed the motor and could not turn it with the gear held in a vice! Light sanding with some 320 sandpaper, wiped clean and it can be rotated with the slippery rotor shaft, a quite low torque to be sure.
I have never seen this type of failure posted, and since it was only this one time my plane has every been outside overnight or in the rain, I thought it was noteworthy to warn others of this possibility.
Check on the ground and don't take off like I did.
The shear screw that saved my life. Smart people at TruTrak, thanks.
Rust on the stator, rotor was the same.
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