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  1. #1

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    Double failure HS 325HB servos

    Today I finished a Hangar 9 P-51, 60 size with a Magnum .91 four stroke installed and was running in the engine on the airplane. I ran it for about 10 minutes each for three runs.

    While running about the 3rd time, I noticed one aileron with play in it, and when I put some light pressure on it, it chattered. Then after running I was showing it to a guy and neither aileron worked, separate servos, Hitec HS 325HB,with a Y harness. They had worked as I did a range check during the second engine run period. Got home, ran them and both had stripped gears. I took them apart and the same gear was stripped with 4 teeth off on both servos. Really unusual. They were Karbonite gears. I had a gear from another set and put it in one and the servo works fine again. So I ordered some new ones from Servo City. I ordered nylon instead of Karbonite, but always thought Karbonite was supposed to be tougher (they cost more, too). I can't imagine why they both stripped. No binding, or anything bad except the vibration of the engine out on the wing. Maybe that was enough with prolonged running, but I never had it happen before. Maybe it was running at the resonant frequency of the wing/aileron assembly?. It was the driven part of the gear that drives the final output shaft gear. So I guess vibration of the ailerons would put stress on those 4 teeth engaged where it sat at neutral during the engine running. Not sure how to prevent it again except maybe no long runs on the ground.

    Do you have any solution or experience with this ever happening before?

    George
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  2. #2
    MikeMayberry's Avatar
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    RE: Double failure HS 325HB servos

    How long were your servo arms? Personally I think that basic standard servos are not the right choice for a .91 powered model; I would consider a higher torque metal geared servo.

    Mike.
    Hitec RCD Rep
    http://www.hitecrcd.com

  3. #3

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    RE: Double failure HS 325HB servos

    Hi Mike,
    Servo arms are the standard 2 blade arms came with the servos. I am using the outside holes to reach through the wing panel. I have used standard servos in other .91 powered planes with no problem. They didn't shake the wings like this one seems to do though. Everything is very tight. This plane hasn't been flown yet. It failed just with the engine running. Picture of the installation is attached

    What metal gear servos would you recommend?
    George
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