pic: CGX-125, 57 Sport 18:1 Cycloid Stage




This is CGX-125, a cycloidal gearbox with an 18:1 reduction ratio made to fit the output stage of a 57 Sport. It adds above 0.94" to the length of the gearbox, which is way more than I would like, but is a result of the limitations of the 57 Sport. However, it is far more robust than other cycloidal gearbox designs I have uploaded due to the longer gears and larger teeth- fitting of the 57 Sport.
This uses 4 unique custom parts: The housing, the two gears, the input cam shaft, and a bronze bushing. The carrier is the same one found in the output stage of a 100:1 Sport, however, it can be added onto any variant of the 57 Sport. The most likely configuration would be as an addition to the 16:1 to make a 288:1 gearbox.
I will probably never use this due to the complexity of machining the ring gear and the low ratio/long length, but it was a fun afternoon experiment.
(This is missing two holes that are in the CAD now)
CAD available here in the CGX-125 folder: https://workbench.grabcad.com/workbench/projects/gcxnb8i8brarEzDXAL7In8SeD-xeuWmarI73f5s6ioPdgL#/space/gc0KZjGz-ib-PcF-_CdNI2gYF1GGPRtLo8SoEKAOByhg3y


Where can I find more information on cycloidal gearboxes? I have seen them here before, but I cannot understand how they work. Have they ever been used on an FRC robot?

Very cool assembly nonetheless


This is really cool! If I understand cycloidal gearboxes correctly, wouldn’t the method of reduction result in a lot of vibration added to the output shaft? I guess you said you wouldn’t use it anyways, but I’m just curious.


The Wikipedia article on cycloidal drives has a good animation of it, but it’s hard to wrap your head around. Harmonic drives actually follow a similar motion, if you’re familiar with those.
AFAIK nobody has used these in FRC, but I did make a Versaplanetary cycloid stage some time ago. Look up CGX-108 for more details on that.

The only time a cycloid adds vibration is when you use only a single gear in the reduction. This gearbox uses two gears that are 180* out of phase with each other, so there should be no vibration introduced to the output.


Is it possible to backdrive?


A bit of a tangent but there’s a pretty cool ebike midrive kit that uses a cylodial gearbox. The 2 inch wide gearbox handles 6KW of power! It’s designed and manufactured by just one guy in his garage.

I’ve been kinda skeptical of the practicality of cyclodial gearboxes outside a controlled industrial environment. Things like this mid drive and your designs have started to win me over.


Ah, that makes sense.

If not, that opens up a lot of options (ignoring the manufacturing difficulty)


Only if the efficiency is pretty low, which (fortunately?) it should be. Theoretically I’m looking at around 60% efficiency, and with other losses it would be non-backdriveable.


That is super nifty! Gives me some ideas with what I can do with this one too.


I really like this design!
I’m going to 3d print one when I get a chance. I’ll share my results.


Here’s a good video on cycloidal gearboxes: https://youtu.be/dYVPU47c9WA

(It’s AvE for those who know his channel)


I’ve modified some of the files slightly to 3d print them without support. If anyone else is interested in them let me know.