BTW, with this sort of un-synchronized gear engagement mechanism, there is a small but non-zero probability that during the engagement process, as the motor is moving to the right, a tooth of the left gear will be perfectly aligned with a tooth of the idler gear. If that happened, something could break. It may help to make the motor rotate slowly during the engagement process. Also known as "grinding" 
Yeah I thought of that as well, generally I can move the motor slowly, it's a geared stepper motor with 0.072 step angle, so it will move pretty slow whether I'd like or not, but to move it I'll must have it connected, if I could, I'd try thinking of a way to push the shaft back with it being perfectly aligned.
I can probably move the focuser itself slightly, which will move the gears and that way be able to set it properly, or set a very small lever to the middle gear and rotate that which should also result in the same principle I think?
Would that work? Thanks
I'm not sure how easy it would be to manually adjust to focuser so that the gears mesh perfectly. I suppose it could be done, but it sounds finicky. Not sure about your lever in the middle idea.
I'd try monitoring the linear actuator (or whatever) current during engagement, and the instant it starts to spike (before full engagement), stop and retract, rotate the motor a smidge, and try to engage again.
Also, a bit more complicated, but you could put a spring between the linear actuator (or whatever) and the motor, so that if the gears failed to mesh, the spring would compress (instead of the linear actuator breaking something or stalling). Then when the motor starts, the gears may engage (with a bang)... Also, the spring would have to be stiff enough to sufficiently resist the axial force generated by the motor gear.
Can you design the motor mount so you can pivot it to engage/disengage the gear? Solenoid or small motor/screw to move the mount.
Paul
Thanks, but I wonder if such approach is actually the right one for me, it sounds like it could get slightly too complicated in terms of how to make it compact, functional and lightweight.
I'll need to further think about how I'd like to approach this
Edit - don't know why it set the reply to my own comment instead of @DaveEvans
An idea I had with this approach is to have an eccentric mount, so the motor shaft is still centered, but I can move the mounting sort of up and down(or right to left) via the eccentric mounting motion, but I wonder how I could make this approach without suffering from lots of backlash.
Hey, can you suggest which bevel gears would I want to use? There seems to be a few types, and I'm really note sure(number of teeth, material, etc, etc). I need a 4mm diameter shaft, at least for the motor shaft, others could vary I guess, but maybe it would be nice keeping it all the same. Regarding size, the smaller the better, if I could find something below 20mm it would be great.
Thanks!
Google for "dog clutch" and look at the images. There are some you can even 3D print.
Paul
Any of them should be fine.
This is a great idea, but I'm having trouble finding any in hobby-scale size (I'm interested in doing this, too, for a project I have in mind.) A dog clutch could be kluged with two of these, face to face...
Of course, just the tips would engage, but maybe that would be enough...
Did you see any pictures of dog clutches you can 3D print and use? Pin one side to the motor shaft and pin the driven shaft to the other side of the clutch with a sliding split in that 1/2 of the clutch. Mechanism to slide into mesh and out is you choice.
Paul
Another idea is to use a planetary gear set. The motor drives the sun gear. The planet carrier connects to the focus mechanism. When the ring gear is free to move, the focus mechanism is free to turn by hand. When a * keeps the ring from moving, the motor can drive the focus mechanism.
- = a latch controlled by a servo, solenoid, or.....
Apparently 3D printing planetary gears is a thing.
The main issue is that using a planetary gear would change the gear ratio which is already what I need, so even the with the smallest 1:3 ratio it would be too much.
For the time being, this is what I think of going with:
2 bevel gears, 1 connected to the focuser shaft, the other connected to the motor shaft, so that gives me a 90 degree angle and the motor will be standing with the motor shaft downwards.
I plan on having a 3D printed part that will be going from the top to the bottom holding it, with this being connected to the actual cover I'll have for the whole assembly which will include outer threads that I'll thread the thing that will hold the motor, by screwing that in and out I'll engage/disengage the motor's bevel to the focuser's bevel.
I tried to check out some other solution for pushing the motor up and down(springs, etc, etc), but I think manually doing that will give me overall the best results in terms of how tight(or perhaps the opposite to prevent binding) I'd want the gears to be. Of course I'll need to be very careful about how I engage it, but it should be ok.
That might not be the best design, but I think it's a fairly easy one to make.
Sounds good. Please share some photos when you're done!
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