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I know solidworks is fine, so now I need to figure out wtf is going on with rev1...
Next Steps
Obvious next steps are testing and refining. Here are the things in particular I want to do
- reducing diameter and adding cutouts to optimize weight
- See how many bearings I can replace with plain bushings to save on cost/weight
- Use thinner cycloidal discs (gonna have to figure out the cam shaft load and see if smaller radial bearings are suitable)
- Test out cycloidal disc fit into the output housing (3d printed or machined)
- Test how the bushings
- See if rolling ring pins are usable compared to the fixed ones I have
- get the damn cam shaft mate to work propely before my head explodes lol
I've linked all of these parts for rev 1 Fixing Prototype 1
Now I needed to figure out why prototype 1 wasn't working. I set up a test assembly with one disc, the eccentric shaft stackup and the ring pin housing. After adjusting the parameters of the motion study to match the testing above, I learned that the motion study once again, did not work. I made a super simplified cam shaft and re tested the assembly, and found good results:
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I ran into more issues when testing dual disc set up. It's a lot to explain so I wont discuss it all, but pretty much I wasn't able to get the motion simulation running properly. I ended up making a bunch of minor iterations to the discs, so I removed the ribs as they were making it difficult to iterate. One thing I also did which was a really good idea was add alignment cutouts. The two holes identify the optimal location to place the discs in initial installation, which will be very helpful for actual assembly.
Finally Getting A Working Motion Study
After a lot of labour and minor revisions, I finally got a working revision. I re CAD-ED disc 2 from scratch, and manually mirrored the disc on the origin rather than using the sketch schematic. Tbh, I don't think this really matters - the main fix will be discussed in a bit.
I made the alignment holes thru holes, and still haven't added the ribs back to the design yet. Will do that later, it's not super important for this initial revision anyways.
I also took the dowel pins out of the output shaft to let them rotate on their own in the simulation.
Lastly, the main thing I changed was the 3D contact resolution of the motion study. I changed it from 50-70 which seemed to fix my issues. Everything seems to work fine now.
Check out the motion study!
cycloidal drive prototype 1.mp4
Next Steps
This initial design is mainly intended to create a bare bones design we can try out with minimal parts to fabricate, as we don't have access to our campus machine shop right now. There is a LOT of stuff I think I need to figure out through testing:
- reducing diameter of the entire actuator and readd ribbing/cutouts to minimize weight
- See if I can replace the flanged bearing with a plain bushing for lower cost/simplified assembly
- Use thinner cycloidal discs than 12mm. 12mm is the smallest width of needle roller I could find on McMaster, so once torque calcs are finished by Mathieu I'll get an idea of the load on our joints and see if I can switch to a smaller profile/thinner bearing. I'm thinking some bearing is going to be necessary here rather than a bushing, as minimal friction is really important on the cam to properly transmit the motion of the disc
- Investigate the feasibility of adding sliding/rolling ring pins (instead of solid). Once torque calcs are done, I'm going to look into how feasible it would be to add free rolling shafts on the ring pins to reduce friction. All other teams who design their own drives go with solid ring pins, and I think that is to simplify their assembly and to make sure the cycloidal drive doesn't fail under higher loading (as free rolling rin pins can break or deform with too much force applied)
- See if a key way is necessary instead of set screw on cam shaft
- TEST OUT THE FIT. Building this ASAP would be very useful. I think the best way to test this would to be to print out and test the first few iterations of this gearbox. We would install OTS components and see if it actually works - see how the tolerances play out and whatnot. This designed is also adaptable to be made with metal, so once I learn from initial prototypes we can get these fabricated at a machine shop for further testing. 3D printing iteration before metal fabrication is highly recommended by Monash, and even though tolerances don't translate exactly I think testing with 3D prints is a good way to validate design.
- Loading testing would also be very important to perform, with a flat lever attached to the drive to see how the torque transmission actually plays out. This would also let us test for backdriveability and backlash.
- See if we need to install bushings/bearings on the radial holes on the cycloid disks. Right now I think we may be able to get away with just having the bushings on the output shaft hub and greasing up the dowel pins
- Make our own dowel pins. This would really free up the geometry for the design and they are super easy to make on a lathe
- See how the PTFE sheets work out as a low friction medium. I'm a bit suspicious that they will just wear out and die super fast - in which case some grease or even a thrust bearing could be used as an alternative
All of these parts for rev 1 are in the 2022 folder, so take a look. PLEASE give feedback in the comments below 
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