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I'm trying to come up with an engage/disengage mechanism for my stepper motor. It will be connected to something that I'd like to be able to move manually as well, and since it's a geared stepper motor with high gear ratios, it would be very hard/impossible to move it manually, therefore I'm trying to think of a mechanism that will allow me to engage/disengage the motor from the assembly.

I tried to look at various solutions, but still couldn't find something that will work for me. I'm using a pretty small stepper motor(under miniature stepper motors category), and the application needs to remain small, so big additions would not work out for me due to lack of space.

I tried to look at electromagnetic clutches, but they are extremely expensive and rather big, so that would not work. I was able to think of 1 possible solution, but I don't know how to achieve that: Basically, if I'll have a stepper motor where the shaft is not centered, I could perhaps by rotating the motor on its axis engage/disengage the motor from another gear part. The issue for me is that I'm using a centered geared stepper motor, so I'm not sure how I could achieve that offset, I searched for some gears that will allow me that, but couldn't find any.

I own a 3D printer, so I can generally print whatever I need, but I'm not sure I'd want to print gears etc, as they could wear quite easily, so I'd rather avoid that.

Any suggestions would be much appreciated. Thanks.

Edit - Basically, I'm trying to replicate this mechanism: youtu.be/TN5hnE2UnbU?t=287

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  • $\begingroup$ rotating the stepping motor is a good idea ... it is not necessary to find a motor with an off-center shaft ... rotate the motor around one of its mounting holes ... use another motor to accomplish the task $\endgroup$
    – jsotola
    Sep 30, 2021 at 16:01
  • $\begingroup$ or put the motor in a slightly eccentric housing - I suspect how the original product does it? $\endgroup$
    – Jonathan R Swift
    Sep 30, 2021 at 16:28
  • $\begingroup$ Per comment below, application is manual / auto focus in a telescope. Maybe a differential gear could be used for this? Would want to set up enough friction on the manual input side so that the motor input's movement goes all into the output. $\endgroup$
    – Pete W
    Sep 30, 2021 at 16:39
  • $\begingroup$ @jsotola I think using another motor is not really an option here, it will make it too bulky etc, but Jonathan's suggestion is actually very interesting, instead of actually rotating the motor on it's axis aiming for it to be off centered, I could make a slightly bigger housing and just move the whole motor somewhat up and down along the edge of the housing, possibly achieving the same effect. Thank you! Pete, you're right, I've added that. Can you share a bit about how I could utilize a differential gear? Any image link you could possibly share? Thank you all for the help! :) $\endgroup$
    – emeseoeo
    Sep 30, 2021 at 17:23
  • $\begingroup$ re: differential gear - the two "inputs" are the manual knob and the motor shaft (after gear reduction). What the diff does here is that when one of the inputs is immobilized, it transmits the other input into the output. The motorized shaft, when inactive, is effectively immobilized by the high ratio of gear reduction. The remaining step is to do the reverse, make the manual input effectively immobilized when not used. If the output is low load (somewhat common for optics), adding more friction than this to the manual input shaft will do it - rotation from motor will go to the output shaft. $\endgroup$
    – Pete W
    Sep 30, 2021 at 17:32

1 Answer 1

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I would probably go for a belt tensioner.

enter image description here

figure : Belt tensioner (source tecscience)

i.e.: at some point in the assembly install a belt between two pulleys and use a motor to engage the tensioner.

This is a very simple arrangement, that should satisfy your criteria. The only drawback is that it can be a bit bulky.

Notes:

  • you can use a toothed belt to minimise belt slipping (if that's crucial)
  • you can set it up so that you can rotate manually the stepper motor that engages the tensioner.
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  • $\begingroup$ Thanks for the comment, but I'm afraid it won't really be a good enough solution for my needs, as you said, it's a bit bulky. I need to keep things small, compact, and lightweight sadly :( Would you perhaps have any other suggestions? Thank you :) $\endgroup$
    – emeseoeo
    Sep 30, 2021 at 12:44
  • $\begingroup$ Unfortunately, nothing simpler and/or cost effective so that you can produce it with 3d printing at a more compact form comes to mind. At least not something with trouble free operation. Maybe some else will be able to provide a better solution to your needs. Are you planning to build many of those? And what is your budget. $\endgroup$
    – NMech ♦
    Sep 30, 2021 at 12:48
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    $\begingroup$ Sure! Appreciate you trying to help. Basically, I'm trying to replicate this mechanism: youtu.be/TN5hnE2UnbU?t=287 This needs to be small, compact and lightweight for my needs. I plan on making 1 I guess, maybe maybe 2. I don't really have a set budget, I find this engineering interesting, but I wouldn't want to spend hundreds of dollars on this. Thanks! :) $\endgroup$
    – emeseoeo
    Sep 30, 2021 at 13:14
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    $\begingroup$ @PeteW You're right, I've added that to the question. Thank you. $\endgroup$
    – emeseoeo
    Sep 30, 2021 at 17:23

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