Servo mods for more shaft turns

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Servo mods for more shaft turns

Postby Rick N » Tue Dec 11, 2012 1:46 pm

I'm just an ME, so I don't completely understand the black boxes too well. Can somebody explain why gearing a 10-turn 5K ohm pot to a servo output shaft does not provide 10 turns on the output shaft? This is assuming that the mechanical limit stop and original pot is bypassed/removed, etc.?
Rick Noddin - AMYA 1645
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Re: Servo mods for more shaft turns

Postby bigjohn » Wed Dec 12, 2012 1:07 am

hi Rick, I hope I can make this sound simple, on a regular servo, the arm moves 90 deg. so the pot only moves 90 deg, so if you take 90 deg of a 5k pot you get 1250 ohms, so the same thing happens on a 10 turn pot you get 2.5 turns, a easy way to stretch a servo is to put a 2.2K resistor on the 2 out side leads of the pot, this will give you about 2 times the rotation
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Re: Servo mods for more shaft turns

Postby Rick N » Wed Dec 12, 2012 2:00 pm

Thanks for the info. That clears things up a little more. So the pot provides some low and high resistance values corresponding to fully retracted and fully extended positions of the output shaft. So the increased travel pot that would replace the stock pot, needs to provide the same two extreme resistance values. It seems that the actual centered position of the pot may not necessarily lie at the required centered resistance value, but instead only be the resistance value half way between the extreme values. In other words, you could use a pot with a higher max resistance than necessary, as long as the range needed is included. It seems that resolution is now in question, so that maybe to optimize that, I would need to use a pot having pretty close to the actual resistance corresponding to max throw of the stock pot. Then whatever number of turns of the output shaft desired would have to be geared to the number of pot turns corresponding to the resistance range found previously, right?
Rick Noddin - AMYA 1645
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