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Increasing servo revolutions

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Old 01-25-2013, 04:02 PM
  #1
agthomson
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Default Increasing servo revolutions

Hi everyone.

I need to modify a hitec hs 785 sail winch servo so that it rotates 3 times the origional amount - just over 9 revolutions - thus realing 3 times as much thread.
I've already tried larger drums on it but the increased load was too great. If i gear down the pot will that work? Not sure.Any Ideas?

Thanks
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Old 01-27-2013, 04:07 AM
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mfr02
 
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Default RE: Increasing servo revolutions

This would require quite major surgery to the control. 
Does it actually need to be proportional?  If not, just lose the electronics, including the position pot, and fit an ESC to work the motor.
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Old 01-28-2013, 09:14 AM
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Default RE: Increasing servo revolutions

yeah unfortunatly it does. so major surgery?
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Old 01-29-2013, 09:15 AM
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Default RE: Increasing servo revolutions

It MIGHT be possible to insert a resistor in each of the outer legs of the sensing pot.  This depends on how long the legs are and how much room there is.  Doing that should increase the travel required to give the comparator the range of voltages it expects, but nothing is guaranteed.  Some experimentation with different values would be needed, but a good starting point would be about half the value of the pot, typically about 5K. Resistors are cheap enough at your local Maplins.  Too high a value could cause it to try to drive past the end of the track, bad news all round.
Normally the pot travels over the middle 1/3 of its track.  Full travel is 270 degrees, a servo arm covers about 90.  Translating this to a 10 turn pot gives 3 and a bit turns.
I have been using non-prop winches for ages, using the idea that I only tell the thing to drive one way or the other until I think its got where I want it, then I let go of the stick.  I've also got boats with propo winches, and they are more fiddly to use - you can't let go of a spring loaded stick without the winch repositions itself.
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Old 01-29-2013, 11:42 AM
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Default RE: Increasing servo revolutions

ok cool, thanks very much. I'm not hugely experienced with servo's, but i'll look into it and let you know how i get on
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Old 02-04-2013, 03:48 AM
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Default RE: Increasing servo revolutions

Oddly enough, just found this - http://www.rcgroups.com/forums/showthread.php?t=1428266
It sounds like your setup, the guy who did it used 2K2 resistors.
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