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Thread: Worm gear in Servo?

  1. #1
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    Worm gear in Servo?

    Hello,

    I was just wondering why servo companies don't use worm gears to drive their robot servos. The motor would have to be just as strong of course, but when the servo is only in holding position, the worm gear could take care of the load while saving precious energy in our batteries (the motors wouldn't have to be activated since worm gears can't be moved).

    I was just wondering if I was missing something here (something I didn't account for maybe?) that could explain why not to use worm gears.

    Thanks,

    Sam

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    Re: Worm gear in Servo?

    Hey,

    I think linear servos do just that.

    As for regular servos, I would think its because the gear ratio in a worm gear is crazy...so the motor would have to spin really wicked fast in order to turn the servo horn at all. For a smaller robot or RC car that wouldn't make sense because response time is more important than holding power.

    DB

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    Re: Worm gear in Servo?

    I wonder how much usable grunt you could get from
    windscreen wiper motors?
    they have worm gears.
    Just put a trimpot on it somehow
    and bingo big cheap servo.

  4. Re: Worm gear in Servo?

    I'm already doing just that for my robot, buy I may have to up it to a stronger motor eventually.

  5. #5

    Re: Worm gear in Servo?

    Worm gears are often not as efficient as other gear systems. Check out this table from http://www.roymech.co.uk/Useful_Tabl...fficiency.html. Still, wiper motors are cheap and have power to spare. Those features, combined with the back drive features that Sam mentioned, make something to consider. I have used 'giant servo kits' from Oatley that try to do this very thing. I had very bad experiences with them as did two of my friends. I may try again using the theory that

    gearmotor + ESC + feedback pot + software = big servo
    Last edited by CogswellCogs; 08-08-2009 at 10:58 PM. Reason: table did not paste correctly

  6. #6
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    Re: Worm gear in Servo?

    Speed, Efficiency, Backlash. Not necessarily in that order. Wrong tool for the job of being a servo, imho
    I Void Warranties´┐Ż

  7. #7
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    Re: Worm gear in Servo?

    Quote Originally Posted by CogswellCogs View Post
    Worm gears are often not as efficient as other gear systems. Check out this table from http://www.roymech.co.uk/Useful_Tabl...fficiency.html. Still, wiper motors are cheap and have power to spare. Those features, combined with the back drive features that Sam mentioned, make something to consider. I have used 'giant servo kits' from Oatley that try to do this very thing. I had very bad experiences with them as did two of my friends. I may try again using the theory that

    gearmotor + ESC + feedback pot + software = big servo
    Thanks for the informative site!

    Sam

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    Re: Worm gear in Servo?

    Found this page with a bit on wiper motors
    http://www.scary-terry.com/wipmtr/wipmtr.htm
    Necessity is not the mother of invention.
    laziness is.

  9. #9
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    Re: Worm gear in Servo?

    His power numbers jive pretty closely for what I found actually measuring and doing real graphs from the Denso motors. I've posted those graphs before, so they're out there somewhere. (Thanks to DB for the motors!) The thing to note is that of four motors, no two behave the same when stalled. One is as low as 13.8A, the highest is 23A+
    I Void Warranties´┐Ż

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    Re: Worm gear in Servo?

    That would be a bit of a problem trying to tune the system.
    What do you think of this one?
    https://www.surpluscenter.com/item.a...tname=electric
    Even has a pot built in.
    Last edited by RevBryce; 09-09-2009 at 03:52 AM. Reason: spelling
    Necessity is not the mother of invention.
    laziness is.

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