pic: Gears in Tube, Mecanum WCD



This is my first attempt at designing a WCD setup. Hopefully, there aren’t any huge errors in the design.

Specs:
Weight, 32.74lb
Max Theoretical speed, 13 fps
Gear Reduction, 10.71:1
6" VexPro Mecanum wheels
Side rails, 1.5", 1/8" thick square aluminum tubing
Front Rails, 1"x1.5" 1/8" thick rectangular aluminum tubing

The design was inspired by 525’s suitcase bot:
https://frcdesigns.com/2013/12/06/behind-the-design-suitcase-bot/

Nice! what made you go with the 6" mecanums over the 4"?
I like how you’ve used 1.5" wide tubing. It never gets any love. :frowning:

Very cool. Good job keep going . Andymark makes something like that as well.

I’m not sure if you can call if a WCD anymore, but nice work anyways.

You can “reverse” the position of the CIM and the wheel in the “gearbox”, putting the CIM closer to the center and the mecanum wheel closer to the outside for more stability in the same size.

I know it’s popular on CD these days, but I don’t think the gearbox in tube setup here is good. You end up needing a wider tube than necessary to pull it off, adding weight across the entire span of the tube, but the tube is substantially weakened right where strength and rigidity is needed the most - at the wheels. Switching to a larger tube to avoid these big pockets just adds more weight to the setup.

You already are making something out of plate to mount the CIMs to the tube - if you really want as few parts as possible, just make one gearbox half out of plate and use the tube side as the other half of the gearbox. There are reasons not to do this (mainly design flexibility if you change your mind about gearing, admittedly not common) but it does reduce part count and would be similar to your current setup with less weight spent on a tube that’s wider than you need.

Even if you change gearing, it isn’t really a problem in most mainstream cases. You can put five different ratios (between 5.95:1 and 12.75:1, surely enough for this application) into the AM Toughbox and variants like the Toughbox Micro with the same plates or housing, and Vex has multiple options too.

So you could still burn in your hole placements without regrets, if you’re smart about it. :slight_smile:

How are the wheels attached to the output shaft? Would a canter levered design like this be ideal with the lateral loads a mecanum drive experience?

The mecanums should be in the tube. Follow the everything-in-tube trend :stuck_out_tongue:

Nice work!

Lots of teams ran cantilevered designs like this in 2015 without problems.

The only thing to be careful of is, if you use a screw + washer to retain the wheel, make sure those stay tight, because more load is placed on them trying to unthread them.

What would you use other than a screw/washer? I’ve only heard of WCDs that use them.

Snap rings are another popular choice, as they don’t loosen, they are a little lighter, and it’s easy to put a groove on a shaft on the lathe if you get the spacing right.