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.


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 Dec 25 '18 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 Dec 25 '18 at 20:34
  • @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 Dec 25 '18 at 21:24

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