pic: CGX-108 front

CGX-108, a 20:1 cylcoidal versaplanetary stage. It is fully compatible with the Versaplanetary gearbox, both input and output. Some dimensions are slightly different to allow for more clearance with the versaplanetary and take up error from machining, but it still fits right on and the external dimensions should match that of a VP.
Uses 3/32" alloy steel pins that are pressed into and braced by the aluminum housing and 1045 steel wobble plates.
There are 2 wobble plates on a 180* phase offset, so if machined properly there should be little or no vibration.
Weighs 0.17lbs, about the same as or a little bit less than a VP gear stage.

See my post below for CAD.
Some dimensions are slightly different to allow for more clearance with the versaplanetary and take up error from machining, but it still fits right on and the external dimensions should match that of a VP.
Weighs 0.17lbs, about the same as or a little bit less than a VP gear stage.

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This Looks Very nice. I know I and my team would be interested in a 20-1 VP stage. Is this something that VexPro or AndyMark may make in the future?

Thank you. Probably not, but you never know!
Download CAD here:

I bet if enough poeple asked then they might consider it.

Correct me if I am wrong but wouldn’t the center gear be wobbling?

If the Cycloidal stage is connected to another VP stage or the output stage, the output gear would be stabilized.

The stage by itself would be useless.

Would love to seem them make this and see what it can do. Prototype it at least.

The two wobble plates are wobbling, but they wobble opposite each other around the axis (input/output shaft) so there is little vibration.
The input shaft has a shaft coaxial with the axle of the VP, and two offet pieces that hold the wobble plates. The shaft is 0.25" in diameter, and the shaft the wobble plates are on are 8mm, and the offset is 0.030". This allow the wobble plates to be put in, then the spline pressed onto the 0.25" shaft.

It should be able to connect to the output stage or input stage of a VP like any regular stage, I’m not sure what you mean. The output of the VP has 2 bearings that constrain it, and none of the ring gear stages have bearings on them.

How would the camshaft for something like this be produced? Is live tooling required?

Probably. It’s possible to do this with a 4-jaw chuck, but the time cost would be high enough to merit just using a 4 or 5-axis lathe.
It’s also possible to do the input shaft on a mill, or make it in 3 pieces to avoid doing external turning on an offset.

For the non-engineering crowd, why would you want something like this? What’s the benefit of this over a standard planetary?

I think Anand should find a machining grant for the team to take on the risk of proof/prototyping. There’s a lot of work in this CAD and I think the team would be very inspired to go through the process of proving a technically challenging design - especially one that’s so tangible with respect to an existing product.

Large reductions in a small footprint.

Cool! It would be fun to see it built and what kinds of problems are encountered. The cam itself is kind of floating, there’s not much to keep it co-axially aligned with the housing other than the cycloid wobble plates, but it looks like a good application.

It should potentially be stronger than a geared stage of a versaplanetary, given it’s relying on a lot of pinned connections instead of a few meshing gear sets. If you stack to many stages of a versaplanetary the output stage can fail, since it sees a lot of torque. If you have a stronger stage, you can handle more load and get higher reductions before breaking things (not that you really need to… the versaplanetary system is already pretty solid).

I’m looking into getting this manufactured. The wobble plates cannot really be machined manually, but I might be able to get the housing and output done on the mill. After that it’s a matter of just getting the camshaft and wobble plates done on a CNC.
The input spline I might be able to do on a lathe by boring out a VP stage, but I’m not sure how to do the output. That would have to be wire EDM’d or something similar. I should send an email to Vex asking how they do it.

For the quantity they run it would not suprise me if they had a custom rotary brouch.

Always amuses me every time :slight_smile:

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.

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.

What’s the difference between a pinned and a roller cycloidal stage?

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.

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