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  • harmonic drive gearing

    Here's a not too bad primer on this type of gearing, with pictures., in case anyone's interested. http://www.powertransmission.com/iss...6/harmonic.htm

    I've been looking without sucess for a similar gearing concept. It has a circular ring gear, same as this, but also a circular inner gear. This inner gear is mounted on an eccentric on the input shaft and is free to roll around the inside of the ring gear, but is kept from turning by a connected lever arm, which has to slide in a groove to accomodate the wobbling around of the inner gear. Because this gear doesn't turn, the ring gear has to turn instead. Similarly to the harmonic gearing, it has a high ratio.

    I've only seen it once, in a cordless screwdriver I believe it was. Anybody know what it's called?
    Last edited by darryl; 01-09-2008, 05:40 AM.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Cordless drills & air drills use sun & planet gears,
    Regards,
    Nick

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    • #3
      Originally posted by NickH
      Cordless drills & air drills use sun & planet gears,
      Regards,
      Nick
      Apparently not quite all of them.

      That's an interesting mechanism Darryl. I haven't seen that before and don't know what it would be called. I wonder if they got the idea from the harmonic drive. It might be fun to build one just to see it work.

      I once sketched out a grinder fixture like a Harig head using a harmonic drive so you could dial in angles directly. That part would have been nice. Cranking the thing for 180 degrees might have wanted an electric drill though unless you just loved carpal tunnel syndrome.
      .
      "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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      • #4
        Darryl,

        Your description fits this illustration in Mechanisms, Linkages, and Mechanical Controls (1965) by Chironis. This particular entry (Ref. 3) was originally published in the magazine Product Engineering, pp 194-198, Feb 1957.

        Allan Ostling

        Phoenix, Arizona

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        • #5
          Allen, that's exactly what I was looking for, thanks for posting that. The version I saw in use was that in the second figure. As stated, there's a slight pulsation in the output- not a big deal for a cordless screwdriver but it probably makes it hard to use for almost anything else. My train of though had been running along the lines of how to minimize or eliminate that error, and it looks like the mechanism in fig. 1 does it.

          It also seems to me that the formula for ratio given for the harmonic drive would work here just the same. One difference- the forces here are not balanced, whereas in the harmonic drive they are.

          One thing I don't understand with the harmonic drive is the so-called kinematic variation. I'll have to study that again.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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