Motor coupling missing?

[Eufrades]

Hello DDeGonge,
I like the design of your 75mm harmonic drive, and I want to use it to drive a sand feeder for my sand spreader on the back of my garden tractor.
I printed all of the .stl parts from the V2 folder, but the wave generator is not the same as the one in your video, its obviously a newer version. There appears to be a coupling of some sort that goes between the wave generator and the motor. I've looked to see if I have missed a file, but I can't find it. Is that hiding somewhere?

Thanks for all of your work,
Eufrades

[gandrewstone]

I think its meant to take a 20T GT2 timing belt pulley with the top flange popped off (based on a comment to the video here: https://www.youtube.com/watch?v=Emvo3bLT-Z4&t=16s). I've got a stepper out of an old epson printer with a pulley that seems to match the wave generator... except I'm not sure because not sure how to pop the top flange off (blowtorch maybe?)

Since you are active, I have a question for you... have you figured out how the top housing is secured? Seems to me like it would just fall off

[Eufrades]

That makes perfect sense! thank you. I don't know why I didn't realize that. I'm going to go looking for old printers now.
As for the top flange of the pulley, the ones that I have are all one solid piece. If the ones you have are not one piece (top and bottom flanges pressed onto the pulley maybe), I would just try prying it off with pliers. If they are all one piece, I would try mounting it to the stepper motor, getting that motor running as fast as you can, and then holding a hacksaw against the part just below the top flange and slowly cutting it off. I'm not sure how else you would do it, unless you have access to a lathe.

I had the same thoughts as you about the top housing. I went back and looked at the video last night where he was testing the torque it would produce, and I think what he has done is bolt the stationary housing and the stepper motor to the testing rig that he built. Then he has pressed the large bearing onto the top housing and pressed that assembly into the stationary housing too. So it looks like the bearing is holding it all together. That's not going to work for my application, so I'm going to have to come up with something different.

What is your application?

[gandrewstone]

Thats a good thought about the large bearing. I bought one so in a few days I'll be able to tell. That probably won't work for me either. I was thinking of using it for a SCARA robot, so there will be force parallel to the motor shaft. Maybe a stationary lid with a thrust bearing between will work for me, or something through the axle... What is your application?

Anyway the gear i had didnt actually fit, off by 2mm, so i made a bigger hole. I also had elephant feet on my flex spline, so i fixed that by raising the teeth a tiny bit off the bed and printing with no supports. I also put the skirt on the inside only. I can give you the bkender models if you want.

EDIT: Yes the large bearing fits directly around the top, and there's a flange on the top to hold it there.

[gandrewstone]

What about the 688 bearings? I think that they were originally on the motor shaft, but are not needed in the V2 design.

[Eufrades]

I think you're right on the bearings, it doesn't look like they're needed anymore. As long ans the motor is mounted solidly to the bottom housing.
My application isn't typical for this type of gearbox, I just needed something with a really big speed reduction in a small package. I'm planning to use it on a sand spreader on the back of my atv. There is a motor there that already spins the spreader, but I wanted to use the same motor to really slowly turn an agitator in the sand hopper because the sand keeps getting hung up in there.
I appreciate the offer of your files, but I think I'm going to modify this quite a bit more to slow it down even more for me.