pic: Thinn drivetrain

Thinnest drivetrain in a WCD form factor by sacrificing weight and machining complexity. It’s the thickness of the 3" colson, the 1" wide tube, and a .25" thick plate, for a total of 2.25".

Had this for awhile but forgot to post.

Haha love it! Those 18000 rmp bevel gears will scream!
Without checking any dimensions it occurs to me you could use BaneBots P60 input blocks as the things the 775s are mounted to.

Maybe I’m going crazy here, but something doesn’t seem to add up.

Excuse my consistency/writing skills… the colson is about 1" thick but I’m used to naming colsons by wheel diameter.

3" Colson = 3" OD Colson, not 3" W Colson.

1" W tube + .25" W plate * 0.875" W Colson wheel, plus a little for clips/spacers, and 2.25" wide is about right.

What on earth is going on with that chain routing? Is that to allow a single run of chain to both wheels?

Clever, but I wouldn’t want to have to deal with getting it in place or swapping it out…

Looks awesome! I had a similar idea a while back, but this looks much thinner!

Here’s my attempt from three years ago:

Link to post

Wow! I guess that’s one way to save bellypan space.

I’d be a little weary of having all 3 wheels run off one extra long chain run. That’s 3x the force going through a standard WCD chain, with a chain that’s probably 1.5x in length and with 4 sprockets on it. I know #35 chain can take a lot, but that sounds like it could be pushing it*. And if it should break during a match, it looks like it’ll take a good chunk of time to replace it (especially if you’re using pre-made chain loops instead of closing the loop on the robot).

*with no actual data or even antecdotal evidence other than pure intuition

I suspect there is one chain going through the transmission, around the center wheel, and around the right wheel - and another chain going around the center wheel and left wheel. If there was just a single chain, the robot would be very good at sitting still as there doesn’t appear to be any chain wrap around the middle wheel.

The number of wheels doesn’t affect the chain tension for the worst case loading (pushing against a wall/another robot with all of the weight shifted to the rear wheels). There are other problems with using a single chain, but it should see similar peak loads as a chain on a standard WCD drivetrain.

How do you mount electronics?

Don’t give 254 any more potential space saving tips to increase the volume of balls their robot can hold. :yikes:

Fit a pneumatic shifter in it and I’ll buy 2.

Wait… you’re telling me you don’t identify parts by how thick they are? Whenever someone says ‘1/2" Hex Shaft Collar’ I look at them like they’re crazy until they say ‘sorry, I meant 0.25" thick shaft collar.’

:confused: :confused: :confused: :confused: :confused:

One of the difficulties about this design that hasn’t been emphasized a lot yet is that you’re going to have a lot of difficulty properly locating all of the motors relative to the bevel gear. Right now you’re relying on screw clearances to do that, which leaves a decent amount of play for positioning the motor. Especially running at such high speeds, a tiny amount of misalignment could really shred your gearset.

You should do one of these that makes 2 “super 775pro’s” by connecting a 775pro to the back shaft of another 775pro.

Then work on shrinking the height of that to sit right on top of the tube, but it’d be a great direct inline compact profile and reduce you to just 2 bevel gear meshes to deal with.

Just a thought.


Yep, that’s one to stay thin while keeping the gearbox on the center wheel.

Getting it the first time should be relatively painless by putting in the idler last and using the extra slack from that. But yeah, replacing it will be a real pain.

Correct. It’s shown in the other picture.

What do you mean? I have all that space in the middle, and turning the motors sideways doesn’t change how they’re connected. This design has several issues, but electronics space is not one of them.

Besides the screw, the motor mounts also fits into slots in the main gearbox plates, similar to a mortise and tenon in woodworking. I’m not sure how that would work out in real life since I’ve never tried it, but it seems to be better than screw clearances in theory. If that plan falls through, I can change to 2 dowel pins that go through the entire gearbox.

Even so, running bevel gears at 18k rpm might not be the best idea…

Wow, is that a possible thing? Has anyone ever tried driving anything from that tiny back shaft?

If it’s okay to stack 3, even 4 775pros? If so, that opens up a lot of options in sideways 775pro gearboxes!

The rules do allow you to modify motor shafts, so go nuts. If you stack too many inline you will get to a point where you are trying to put too much power through a tiny little shaft. Two motors inline might be enough to wreck whatever pinion you use to connect the motor stack to the transmission.