Re: pic: CGX-108 front
 

Always amuses me every time :)

Can this go in both directions, or can it only go in one direction? I remember something about that a while back, but my memory is failing me there.

What practical application would this have? I would imagine this having a slower speed than most gearboxes, but a great amount of power/torque for game elements that would require such.

Re: pic: CGX-108 front
 

It can go in both directions, but has backdrive resistance. Using pins should make it totally anti-backdrive, but I'm thinking about switching to rollers for just backdrive resistance instead.

The 20:1 reduction in the same space as a 10:1 reduction has a few uses. For example, intakes with high-speed motors like BAGs or AM-9015 can easily require more than a 10:1 ratio, and often times a 20:1 ratio could work. This year for 115's elevator we used a 21:1 reduction 2-stage versaplanetary on two RS-775, as well as a disc brake to hold the totes. We could have simultaneously saved a little space and weight as well as removed our disc brake by using a 20:1 cycloidal stage.
Any situation where you require lifting of the robot or something similar that requires full anti-backdrive I would use a pinned cycloidal versaplanetary stage. But if it doesn't need to be that strong and you want better efficiency, a roller cycloidal stage would work better.

Re: pic: CGX-108 front
 

What's the difference between a pinned and a roller cycloidal stage?
Thanks!

Re: pic: CGX-108 front
 

The difference is whether the coupling between the two layers is made of solid pins, or if rollers (long thin bearings) are installed in that location. With rollers, there will be less friction, so that backdrive can work. There are 8 pins in the render at the beginning of this thread.

Re: pic: CGX-108 front
 

<Updates coming in tomorrow>
;)

Re: pic: CGX-108 front
 

You know the drill: video, or it's a bench grinder...

Re: pic: CGX-108 front
 

I briefly considered this, then decided I'm not evil. :D

A video of it working (10:1 planetary, followed by a 33:1 cycloidal stage):
https://www.youtube.com/watch?v=ArUGM51HFVs

A video of a basic anti-backdrive test:
https://www.youtube.com/watch?v=tG_l...ature=youtu.be

I changed the design to use 1/16" pins around the periphery, and found that let me get 33:1 into a single package. I made this one all custom, but the next revision just requires a carrier plate from a 7:1 instead of the modified carrier I had to make (thanks to 649 MSET-Fish for providing 7:1 carriers!)
The noise level is high because the way I machined the housings, I neglected to centerdrill the pin holes before final drilling, resulting in holes that are all very off. The lasercut wobble gears I am using are now too large because of this, and so run very noisy. I will remake the housings next to fix the issue.
Right now I would estimate the maximum non-backdrive torque before the gears slip is around 25 foot-pounds, which is quite low, and the failure mode is that the gears go skew on the shaft as the plastic bores get larger than the shaft over time. Replacing the plastic or using some extra shims to prevent bending on the shafts should fix the issue, but we'll see.
The wobble gears will be replaced with aluminum for some more realistic torque tests soon, and then replaced with steel for the final cuts. For the immediate future, I can get slightly smaller gears lasercut to run it quieter.

As a neat sidenote, I made the offset shafts using a boring head with a backwards boring bar in the mill. At this point I can start from a bar of 3/8" round and turn it into a shaft in around 45 minutes.

Re: pic: CGX-108 front
 

Awesome to see a working prototype! Got any pictures of the inside?

For the wobble plates, I don't expect the plastic to hold up very long at all, but if you have the ability to cut plastic ones easily you may be able to iterate with them until the fit is just right, so you know what dimensions to use for the aluminum/steel versions. Also, will the metal versions be laser cut? I'd be curious if there is any kerf angle as a result of lasercutting that might affect the interface to the rollers. With such tiny pins, the tolerances on all of the parts will probably have a big affect on the performance.

I'm really interested to see how the final one performs! Maybe you could set up a simple bench test apparatus (turn a pulley to wind up a weight, for instance) to test it under different loads. Data is useful!

Re: pic: CGX-108 front
 

Pics of the inside have been uploaded to CD. If you want more specific pics I can get them.
The plastic ones are already wearing out a ton, but I do need to use them for iteration. The lasercutting seems to be accurate to +/-0.001" with almost 0 kerf angle, so I get realistic predictions of what metal ones will do from it.
The metal versions will be CNC'd for now, and wire EDM'd hopefully for the final version.

Re: pic: CGX-108 front
 

This is really cool. How are the gearboxes holding up? Any interesting failure modes observed so far?

Re: pic: CGX-108 front
 

This is a really cool project, and I'm anxious to see the final result commercially available. Although I would be even more excited if you could make your own final stage as well. The Vex final stage has really insufficient mounting strength at high ratios. Two #10 bolts isn't enough to hold the reaction torque (above 100:1 on a bag motor) in our experience.

Re: pic: CGX-108 front
 

Nice! Ever since you posted the CAD a few months ago, I was eager to see it come to life.

Good luck on the final iteration! Hopefully this will be something VEXPro will look into in the future, it really is a nice way to get a compact and high reduction stage for Versa Planetaries.

Re: pic: CGX-108 front
 

While I'm still of the opinion that cycloidal gearboxs are magic, the thought of a 20:1 or higher reduction with limited or zero backdrive in a VersaPlanetary form factor is VERY appealing to me. It could also be a way more flexible and compact solution for applications that many teams currently use worm gearboxes for.

Re: pic: CGX-108 front
 

Thanks! The "good" failure mode is just a ratcheting due to the plastic teeth skipping, and the gearbox still runs afterwards. The more common "bad" failure mode is when the plastic gears go skew on the shaft, locking up the gearbox. Using metal hubs or bearings should fix these issues. I would not use the gearboxes on a robot right now, as the tolerances are all over the place. I'll be fixing that next week.

Thank you, I hope to be able to make this a commercial thing eventually.
We have used the side mounting holes in the past to hold our VPs, so doing that could help. You could also cut 2 more mounting holes such that it holds the VP together; you would use the 2 corner holes that currently house #8 bolts that hold the VP together.

My thoughts exactly! Using the plastic gears allows for ratcheting, so the gearbox doesn't get destroyed by over-torquing the output (like in a collision with another robot), but metal gears if properly constructed would be able to shear the 1/2" hex output before the gearbox fails.

Re: pic: CGX-108 front
 

This is a bit of a resurrection, but has there been any progress on this design? I think this could be a great option for teams wanting to power arms or winches or a host of other subsystems.