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I'd like help coming up with a simple brushed DC motor-powered mechanism that achieves the following.

  • Rotating the motor clockwise causes a linear mechanism (a pin) to arrive at position A
  • Further clockwise rotation does nothing to change the pin position and does not damage the system.
  • Rotating the motor counter-clockwise causes a linear mechanism (a pin) to arrive at position B
  • Further clockwise rotation does nothing to change the pin position and does not damage the system.
  • Removing power from the motor does not change the position of the pin
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    $\begingroup$ This is a pretty common setup for linear actuators. With use of diodes and limit switches, electrically commanding a motor beyond the limit triggering causes nothing to move. If you require the motor to spin at the stop locations, a similar result could be achieved with mechanical means- a ratchet in place of diode should work if you figure the trick of associating limit positions to pawl engagement/disengagement. A screw is typical for converting rotating to linear, and also can fix things in place depending on friction and pitch of screw. $\endgroup$
    – Abel
    Aug 2 at 12:23
  • $\begingroup$ Sorry, I should have detailed the requirements a bit more, I want only 2 wires going to the actuator (power and ground) with no limit switches, ETC to prevent overtravel. Could you expand more on how a ratchet could be used to limit positions? $\endgroup$
    – user42570
    Aug 3 at 2:59
  • $\begingroup$ Its still 2 wires going to the motor. Limit switches are wired into the "motor" itself. Hop on ebay and search "heavy duty linear actuator" $\endgroup$
    – Abel
    Aug 3 at 3:33
  • $\begingroup$ Oh interesting, I see what you mean with the internal limit switch. I would still prefer a purely mechanical solution since this is something I'd like to make 32x of and 3D printing a simple mechanism is more feasible then 2 switches per actuator. $\endgroup$
    – user42570
    Aug 11 at 3:02
  • $\begingroup$ Simple? By no means is it simpler than a couple of diodes and limit switches (which is why industry opts for the diodes). If you still choose to try purely mechanical and 3d printed, start at stuff like the 1869 freewheel at en.m.wikipedia.org/wiki/Freewheel once you have two of these working in series, figure out how to engage and disengage the ratcheting mechanisms when your part is at travel limits. Every electrical contraption has a mechanical equivalent, but how long would you need build a mechanical computer? $\endgroup$
    – Abel
    Aug 12 at 0:50

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