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How big would this gear need to be?

  1. Nov 17, 2013 #1


    So I read the article above and it gave me an idea, I want to find out if it is possible to build this machine, but with a reverse gear set on the other side of the concrete that makes it spin back up to the original or close to the original speed. Obviously with the gear ratios he has used the losses and slack in the drive train would never work however I propose a this alternate design:

    200rpm motor like he has only the block of concrete is on a gear that turns maybe every 8 hours, to the human eye this would look like it is not moving, then put the reverse gears back up to get it spinning on the other end eg:

    5 * 10:1 gear reductions, then 5 * 1:10 gear step ups so rpm would be:
    200, 20, 2, 0.2, 0.02, 0.002 (8.3 hours for 1 rpm) then step back up to 200 rpm.

    How much torque would the middle gearset need to be able to take and hence would it be physically possible to build this machine and have it fit in your room? Even if you require an extra 6 or 7 gears on the reverse side to get the speed visible to the eye due to the torque losses.
    Last edited: Nov 17, 2013
  2. jcsd
  3. Nov 17, 2013 #2


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    Staff: Mentor

    Neglecting losses in between, the torque the last axle needs to rotate multiplied by the reduction factor (10^5 in your example). And then you have to make your gears really precise, otherwise they will not rotate uniformly.
  4. Nov 18, 2013 #3


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    Science Advisor

    High reduction ratio worm gears have high friction and cannot be driven backwards.

    Using gears to speed things up is fraught with problems. Overdrive gearboxes are an example.

    You will also need a flywheel on the output to maintain a smooth rotation rate.

    Will torque break the input gear before it starts to move the output? Even if you use spur gear or epicyclic gears it may be necessary to provide some source of vibration or power to the output shaft so as to overcome static friction.
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