Hello, 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.
A slipping clutch is often used for this. You arrange the operating torque to be higher than that needed to move the load so that it doesn't slip when the motor is operating.
However if you want to keep track of the actual position this isn't the way to do it, you'd use a "jog" control to manually drive the motor, allowing the software to track the change in position made "manually". Jog controls often have a couple of speed settings and two buttons to control forwards or backwards adjustments.
Thanks for the reply, I tried searching about slipping clutch, but couldn't really find much about it, or at least, couldn't find something that I could buy to fit my needs.
Regarding tracking the position, I'm actually not really sure how crucial that is. It's important only when the motor is engaged, but even without it, it's not that big of a deal really, and when the motor is not engaged, it probably won't move either, so I don't think it should matter, unless I didn't understand you correctly
Jog control sounds interesting, but do you have any ideas on how I could find the hardware to implement that?
Thanks for the comment, I tried searching for that, but once again I couldn't find something that's reasonable in both price and size.
Do you know of anything specific that could possibly be used with a motor shaft?
Do you think it would be reasonable designing and 3D printing such clutch without having to deal with huge backlash?
How will the stepper motor be connected to the rest of the mechanism? Via more gears? A belt?
Until we get more information, I'm thinking in terms of something - a gear, an idler wheel - that is moveable in and out of engagement using a servo. I'm not sure how a spring clutch could work, as I thought they were essentially uni-directional drives, so they only disengage in one direction. Happy to be shown wrong about this.
Perhaps you could give us more detail about how the stepper is coupled to the mechanism, and what the mechanism actually is.
Thanks for the comment.
Well basically, I'm trying to achieve something similar to this mechanism:
This is a telescope electronic focuser, since it has high gear ratios, you can't manually move it and I would like to have this option.
The way it will be connected is probably something like:
Motor D shaft>Coupler>Telescope shaft
Between that I'm trying to achieve this engage/disengage mechanism, I'm actually quite shocked that I can't find anything useful. I thought of quite a lot of ideas that could be possible, but can't find any metal part that I can use to achieve that, and once again, trying to avoid 3D parts.
Achieving that mechanism is not necessarily that hard, but finding something that's not gonna cost that much, is quite small, and doesn't create huge amounts of backlash is not easy to find.
If only I had a lathe mill, life would've been much easier, but I have to rely on either 3D printing or some actual metal parts I could find.
Thank you, it is. I need to think some more about this, but as there is nothing other than a coupler between the D-shaft and the telescope shaft, our choices are limited. Some kind of electromagnetic clutch (perhaps even something you fabricate yourself) is still on the table.
Bearing in mind you will be laying hands on the telescope to manually focus it, would it be feasible to have a manually operated clutch - something that you can slide in and out of engagement, so to speak?
Yes! A manual clutch is an option, of course.
I have no issues making something myself, I even tried thinking of few different clutches, but I can't think of anything I can self made(with 3D print) that would not create tons of backlash by that mechanism.
I just came across these:
But the description lacks, and I'm not 100% sure it does what I expect.
One way would be to mount the motor on a sliding rail and move it (parallel with the motor shaft) with a linear actuator (or servo or...)
A bevel gear would be mounted on the tip of the motor shaft (say, the left gear in the following image).
Moving the motor would engage and disengage that gear from another bevel gear, an idler (the middle one). When engaged, the motor would drive the idler, which in turn would drive a third bevel gear (the right one) that is attached to the telescope shaft.
Interesting idea.........That's sort of a differential gear that's instead of having a single input turn 2 outputs, turn 2 inputs into 1 output?
That's surely possible, but I think requires a lot of precision with the way I design it so the output won't wobble.
I can use 2 similar small sized bevel gears with 1:1 ratio instead of having 1 big bevel gear in the middle, right? If I can make it small enough, then that is pretty good...
The only input is from the left gear, which is attached to the motor. The output is via the right-hand gear, which goes to the focus mechanism.
The only purpose of the middle gear, the idler, is to transfer power from the left gear to the right gear...but only when the linear actuator (or whatever) has moved the motor to the right, so that the left gear engages the idler.
When the motor is moved to the left, so that the left gear is NOT engaged, you will be able to turn the focus mechanism by hand, which will rotate the right gear and idler, but not the motor...
If you use the same size of left and right gears, the output rotation will match the input rotation (but be opposite direction). You could use a smaller idler (middle gear) than the one shown...its size has no effect on input vs output.
Suggest checking out the linear bearings, pillow blocks, shafting, and gears offered by servocity.com
Whether that meets your backlash expectations would probably have to be proved by testing an actual setup. The parts aren't all that expensive, so if it sounds promising, I'd suggest going for it.
I have no affiliation with servocity. No doubt there are other similar vendors, but they seem to have a good assortment of compatible parts at reasonable prices.
I see, well yeah that's obviously better ^^
I thought that once the motor shaft is not engaged the middle gear, when manually rotating could rotate the focuser, and I think it will work, but completely useless
That sounds pretty awesome, the only thing I'm worried about is backlash when changing the motor direction, if I recall(might be completely wrong), these types of gear tend to have a lot of backlash?
