pic: PBL-104: Planetary Ballshifter

A gearbox I made this morning. There is a 11:60 gear reduction from the CIMs to the shifter shaft (this can be increased to a 12:60 reduction). From there, it can either undergo a 1:1 reduction to some 32t #25 sprockets or a 3:1 reduction via a planetary gearset to the same.
It utilizes a 1 Module (~25 pitch) 60 tooth internal gear to make an epicyclic gear set with a 30 tooth sun gear. It can shift between a gear ratio of 5.45:1 in high gear or 16.36:1 in low gear. For a 5" wheel, that means 21.2fps and 7.1fps free speed; a fast combo for a large field.
Using a 12t pinion, you can get 18.5fps and 6.2fps from a 4" wheel, a solid set of speeds for a 6-cim drive.

A .stp (STEP) file is available here:

A shifter piston has yet to be added, but you can put it either in the front of the gearbox or in the back.
This is not WCD compatible, as the output is via the two 32t sprockets only.

Very nice. Lightening pattern seems conservative in some places, but that’s not a bad thing. The use of a module gear is a nice touch as well. Only question is how will it mount to a frame, but I’m sure I’m just not seeing it.

Your designs are getting a lot better - keep up the great work!

The standoffs that hold the gearbox together are 10-32 tapped, so you can just screw the plates on. The front view of the gearbox shows these are countersunk, but that’s because I wanted a single style of plate to work for both sides (in real life you would just not countersink the front side).
The module gear is because there are no good diametrical pitch gears available.
Thank you!

Also, I forgot to mention that the weight is 1.6lbs as shown, which can be reduced by lightening the 60t gear.

Is the sprocket sandwiched between the planetary gear set and the motor output? It looks like the sprocket’s face is being attached straight to the planetary gear plate?

Really, really cool design!

Pretty much. The sprocket is attached to a custom versahub, which acts as a carrier plate for the planetary gearset and can be shifted into to skip the 3:1 reduction from the sun gear to the carrier plate.

That’s not a swerve drive!

But seriously,

It really is.

I see that part, but I don’t see how the sprockets actually attach to the custom versahub, at first I thought the pins that held the planet gears in went all the way through the bolt pattern on the sprocket, but thats not it, so?..

Also, I would recommend these guys for the standoffs between the 2 plates, you can hold them with a wrench which is better than hoping it they don’t start spinning after a 1/4 turn of the bolt.

I would also try to include mounting holes for an encoder somewhere, maybe the front face. Remember to think about manufacturing method for the plates, I see the CIM boss is set at 0.750, probably won’t fit an actual CIM if you use a water jet…but I have no idea if you’re actually planning on making one of these :stuck_out_tongue:

Again, very cool.

Thanks for reminding me to put mounting holes for sprockets; I actually forgot about those. Right now there are only holes for the planet gears.
Hex standoffs sound good too. Usually I would just tighten both sides at once, but I guess that’s not possible if it’s mounted on a face already.
Usually I use 0.752 for cims, but I guess I got lazy there. Generally a plunge with a 3/4" endmill takes it out to just the right size.
Forgot about encoders, and yeah, I’ll probably stick those on the front face. Alternatively I could put the encoder in the back and put the shifting part in the front, but it remains to be seen.
The day when we buy a CNC I’m going to be experimenting so much…

Looks cool! Where would you plan to get your 5" wheels from? The standard ones from Andymark and VEXPro are normally 3.5, 4, 6, or 8. I would definitely be interested to see a solid 5" COTS wheel because that opens up the world to a lot more possible ratios.

Colson makes 5" Performa wheels, sold by banebots here:

You can get 5" colsons from robotmarketplace, or banebots as stated above.
Because this doesn’t direct drive a wheel from the main shaft (although theoretically you could adapt it to do so) you can place the gearbox in a remote area on one side of your chassis and run 3" or 2.5" wheels.

How do you plan on getting the ring gear? Do you plan to make it yourself or do you have a source for one that you can purchase?

QTC sells part # KSI1-60, which is a 60 tooth 1 Module ring gear. However, it is heavily modified to add mounting holes and remove most of the steel around the enndges.
If you have a CNC it’s not too bad of a modification.

Cool thanks! Yeah not direct driving any wheels gives you a lot more breathing room for ground clearance for sure.

Are the two sprockets in the STEP file intentional?

How about getting the output to the end of gear box too?

Any kind of bearings/bushings in the planetary gears? That part reminds me of an Andymark GEM gearbox which brings back bad memories of bag-n-tag day 2013.

I don’t think you understand how it is designed to work, the sprockets ARE the output. You would have 2 chains running out of the gearbox to 2 of the 3-4 wheels per side of the robot, which would also have double sprockets on them and be chained to the other wheel or 2.

Pretty much. For that reason this is a less-than-optimal gearbox for anything that is cantilevered, as you waste weight on the extra sprockets.

An output on the main shaft is tricky, as it always spins at a 5:1 ratio from the cims if you use 12t pinions. The sprockets wiill change speed when shifted, but not the main shaft.
In order to have an output on it, the sprockets would have to be put on another versahub which is attached to another shaft that is coaxial with the main shaft. Kind of a pain, and there’s no way to do it while remaining within a couple pounds.

Could you replace the 2 sprockets with a gear and put another shaft underneath the whole thing with a 1:1 gear (or not 1:1 if you don’t want) and have a cantilevered output that way?

Not super necessary or elegant, but I don’t see why it wouldn’t work.

The point of this was to reduce weight and keep the single-shaft design; by adding a large gear and a second shaft it loses both of those advantages unfortunately. If I had to make a 2-shaft gearbox I would just make a regular ballshifter (like ABS-101, although I would probably increase the primary reduction if I were to go that route; that gearbox went a tad too fast for most).