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

gearbox
frc1072
planetary
meep
cycloid
1072
57
sport

#1

dcf492787c4d461697e079338dbbd0ac_l.jpg

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


#2

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


#3

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.


#4

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.


#5

Is it possible to backdrive?


#6

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.


#7

Ah, that makes sense.

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


#8

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.


#9

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


#10

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


#11

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

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


#12

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