3
$\begingroup$

I want to make a shaft rotate in 21 discrete steps, from a motor that is turning smoothly.

I am thinking of some kind of simplified clock escapement type of mechanism. Or non circular gears.

I know it could be done by programming a stepper motor. But it will be easier and more fun for me to do it mechanically with 3D printed nylon parts.

This is for a low torque low speed application. About 1 rpm and less than 0.1 Nm torque.

$\endgroup$
  • 2
    $\begingroup$ How about a Geneva mechanism ? $\endgroup$ – William Hird Apr 4 '17 at 16:10
8
$\begingroup$

Geneva drive
3D Printed Geneva Drive

Geneva drive enter image description here



Anchor Escapement (Clock Mechanism)
3D Printed Anchor Escapement

enter image description here

$\endgroup$
  • $\begingroup$ Nice visualizations. $\endgroup$ – MrYouMath Apr 5 '17 at 8:52
  • 1
    $\begingroup$ Regulating the radii ratio between the wheels of the Geneva mechanism you can tune the number of steps to a degree; at a high number of steps (like 21) you'd have a lot of play though, as the curve of the rounded part of the "star" wheel would be very shallow. But if you make the Geneva mechanism for 7 steps and then reduce this further by normal gears in 1:3 ratio, you'll have your 21 steps on output while keeping play to minimum. $\endgroup$ – SF. Apr 5 '17 at 9:00
  • $\begingroup$ How is a Geneva Drive implemented in real machinery? It appears to have a large contact area between static and moving items, leading to significant friction & wear. $\endgroup$ – Carl Witthoft Apr 5 '17 at 13:32
  • $\begingroup$ @CarlWitthoft The faces of the two wheels are not in contact. The only contact is between the pin and the slots on the indexing wheel. This creates a line contact. Depending on the loads and the size of the mechanism, this could be addressed in a number of ways or combinations of ways. The pin and the slot would likely be hardened. There would likely be lubrication. The pin might really be a roller bushing. $\endgroup$ – DLS3141 Apr 6 '17 at 17:01
  • $\begingroup$ @DLS3141 ok, I see. I thought the semicircular part was there to inhibit backlash in the red gear. So why not just a regular toothed wheel for the red and a single-tooth gear for the driver? $\endgroup$ – Carl Witthoft Apr 6 '17 at 17:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.