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Parkzone F4F crash...

Old 03-25-2012, 06:03 PM
  #1  
jnylund
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Unhappy Parkzone F4F crash...

...my second plane, on it's 6th flight, and it experienced a severe pitch-down coming out of a loop. Straight into the ground from 20ft at speed. Upon disassembly I noticed that the elevator was deflected full down and the elevator servo arm had "shifted" its neutral postion 90deg forward. Has anyone heard of a servo doing this in midflight? Spectrum DX6i transmitter, no previous crashes or anything that might have damaged the servo... it seems like a random servo malfunction, but I want to research a bit. I'll ask question about potential repairs in another thread...
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Old 03-25-2012, 08:09 PM
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xmech2k
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Stripped servo? Does it still function? Make sure the arm was fully seated on it. If not, might be stripped gears inside? I've had 2 servos do this. One on my PZ Corsair when one landing gear came out on landing and the aileron servo dragged the ground, and one in my Apprentice. I think I did it accidentally hitting an aileron getting it in or out of my car.
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Old 03-25-2012, 08:23 PM
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jnylund
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Hmmm - I suspect if it was stripped you could hear the gears work in response to the transmitter but the arm would not move? That is not what is happening I'm afraid. The servo arm responds to input, but is in a new neutral position... But servos will strip that easily?

I'm new to the hobby, and this was my first crash, so I'm a bit perplexed...
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Old 03-26-2012, 12:13 AM
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xmech2k
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Well, it couldn't physically have a new neutral position unless gears skipped or the arm wasn't secure. Though I'm not familiar with the inside of servos, so I don't know if the feedback mechanism could move and allow that. In any case, for the price of servos, I'd get rid of that one. I'd open it up for curiosity's sake.
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Old 03-26-2012, 01:13 AM
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quorneng
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The question is did the servo arm end up in the new position as a result of flight loads or (rather more likely) as a result of the crash?
It is possible for plastic gears to 'slip'. They can still work but of course the teeth are severely weakened and the servo must be scrapped.
Why it dived in could have be a servo 'glitch' or maybe an aerodynamic overload on something at the highest speed and G loading at the bottom of the loop.
Personally I would not blame the servo.
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