I need a mechanism so that if a (NXT) motor rotates forward, it moves one gear, but the other stays still, but if it rotates backwards, the first gear does not move, but the second one does.

I found an example solution for one half of the problem here (I would need 2 of these), but that seems like it would take part of a rotation to pick up, and I need mine to be really precise.

I am building this for the Z-Axis/Extruder of the NXTStrap.

1 Answer 1


Would this solve your problem? Depending on the direction of the input, only one axle will turn. Depending on the direction of the input, only one axle will turn

  • Does this solve @Ari Porad 's problem? The best resolution you could get with this device is 1/4 of a turn.
    – MindS1
    Commented Dec 25, 2018 at 0:52
  • ^ Why would you say that? It's free to rotate as much as it wants, because the four-lobed "Gears" will simply slip underneath the angled stoppers, in one direction.
    – RallyToMe
    Commented Dec 25, 2018 at 20:34
  • 1
    @RallyToMe, technically MindS1 is right, it could take as much as a quarter turn until the knob wheel gets locked. This can however be reduced by using ordinary gears, the more teeth the smaller the error at the price of increased size.
    – zovits
    Commented Dec 25, 2018 at 21:24

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