wait what, you can use the outer surface of the bearing? to me that blows my mind, because up until that point my brain was still working in strain wave gearbox space!
Can you share the reducer suitable for the 42-step motor in the video? It seems that the onshape software cannot modify the reducer into a square one. Thank you very much!
Nice video! It's great that you're including some testing too. ( I agree with the other commenter saying that for backlash you should approach from different directions) Have you seen @LeviJanssen 's video of a co-planar compound cycloidal gear? "The Compound Cycloidal Drive - Something Novel" would love to see you make a video exploring this idea.
Now I know about the Abacus Drive, thank you so much! As I understand it, it's a bit different: it uses a second cycloidal wheel on the wave generator instead of a round wheel.
@@MishinMachine Interesting! It would be cool to see a comparison between the two devices, including full characterizations of the drives. This solution seems a lot easier to build, so I might incorporate it into some of my projects!
What would you think about replacing the rollers with small bearings like MR62ZZ? I know it would be more expensive, but do you think that would have a significant performance gain?
Why not. But in this case you also need to use output pins setup like in cycloidal gears instead of a separator. The diameter of these pins should be less than the inner bearing diameter by the amount of eccentricity. So with MR62ZZ bearings and 1mm eccentricity, the pins should be 1mm in diameter.
What a great design, and an excellent vid explaining it! Thanks for the model too! The backlash seems quite good as it is, but I wonder if it could be even further improved by introducing a slight offset between two phases? That could make assembly difficult, but it might not be too bad if you assembled the two phases separately and then applied some torque as you were screwing the two parts together. This would increase friction and thus cost efficiency, but that might be fine in applications where zero backlash was important. With two sections 180 degrees out of phase with each other, is the rotation completely smooth or is there still some input/output nonlinearity?
Thank you! I don't quite understand how to offset the phases. But you can, for example, increase the size of the wave generator wheel a little and use precision hardened steel shafts as intermediate rollers. In my test I used nylon standoff spacers and a tiny offset in separator holes because my old 3d printer is not quite precise. Actually I haven't tested 180 degrees out of phase setup yet. Got carried away by another variant of this drive where this balancing issue should be resolved.
This is great! It would be very interesting to see the actual load carrying capacity and the efficiency of these drives. Thank you for the great video.
You're the first guy Isee measuring backlash with that pointer on a wall, after me, many years ago :D (I used to do it at 10-12m distance, for greater acuracy) Careful: at 8:35, going one way, returning, then going that same way and returning you're not measuring backlash, but repeatability. To measure backlash you need to go one direction, return to zero, mark the position, then go the opposite direction and then back to zero, mark the new position and measure the difference. You might also want to measure the same under a relevant load. You will find backlash increasing with the load. That's called torsional rigidity and the smaller is the better. With plastic I imagine quite a load of it. On my Aluminium + Steel pancake system I was measuring 0.75 arcminutes under zero load (like you measured here) but 10 arcminutes extra per every Nm of torque added. Anyway, amazing work, especially explaining it and creating the parametric model!! That's awesome!
I think the backlash measurement was when he attempted to manipulate the actuator by hand. It would require a lot of care to automate a backlash test because any asymmetric load is likely to take up the backlash (e.g. the action of gravity on the mass of the laser pointer in this setup).
@@cooperised He's using a laser to measure, which is clear evidence he's perfectly aware that any external load can have in impact on the measurement, and that measuring at a distance is orders of magnitude more precise than the test people usually do (wiggle it like there't no tomorrow and concluding there's no backlash based on the perceived stiffness). So I don't think he was trying to Measure backlash when attempting to manipulate the actuator by hand, just to Assess if there's a gross amount thereof. Also, the laser pen is so light that the friction forces inside the unit are overcoming any imbalance the pen might induce, so that's negligible. Ask me how I know :D
It's also possible to make a cycloidal where both the disc and ring use the squiggly curve, and have rollers inbetween. But it halves the reduction ratio and doubles the eccentricity. Tomato1107 has a video v=73DANPATrQU with python code to generate the correct squigglies, although the simulation has the disc spinning in place. I posted a comment there on how to modify the code to show the eccentric motion (which is necessary for to to actually function as a reducer)
Interesting design! But since the rollers have to move radially to follow the squiggle, I don't think there's any way for them to push tangentially on the output carrier without sliding friction. That will probably be your ultimate torque limiter. I wonder how it compares to a cycloidal of equal size.
This is a really really cool design! I love it ! The only thing I'm wondering is what about using mini ball bearings for the rollers? I can see that the roller cage is one point where it's sliding friction. It's probablly not bad, but seems less optimal. It is certainly not an option for small gearbox, but maybe an option for large gearbox?
@@MishinMachine Actually looking again at the video, I'm not sure how would you use the ball bearing as roller. I just realize the separator is not moving in the ecentric motion, which mean the bearing needs to go in and out on the seperator.
I tried to test the load, but I haven't done it before and only had laggy Ikea scales. The results also really depend on the current of the motor driver. In my tests, the highest load was 1.4 kg on a 20 cm lever for a 20:1 reducer.
@@MishinMachine So around 28kg*cm or 2.8Nm? holding torque and active torque can be a bit different but if we say nema17's are around 0.2-0.3Nm So its somewhere between 50-70%efficient? Would love to see more tests ^^
Yes, I tested them. It was my second option after the brass round standoffs shown at 2:39. You can try different options as long as they are round 😄. The model allows changing the diameter and height of the rollers.
It has about 6 solid contact points....taking in the fact that these are plastic gears...I would bet it's pretty strong for its purpose. I'm more worried about the wear of those belts in those extreme angles...
@@b03tz At the end you can see wear on the edge of the belt. And if all 6 points of belt contact mesh properly, it's either a miracle, or very careful design.
@@criznachhow would that be a miracle? If you design a GT2 gear, it would be obvious those teeth all align. Only problem is that the belt goes straight for a tiny bit that might pull on the teeth. The belt wear is a bigger issue I think!
@@criznachfor sure for sure! And in that case I guess if he calculated the rollers so that exactly 1 or 2 teeth are “skipped” it would be quite amazing!
