4" Wooden Mecanum Wheel

[TheOtherGuy]

This is my second year in college, and I've been looking for something to keep me busy (robots?). I decided to create a mecanum robot roughly half the size of an FRC 'bot as a testbed for a variety of mechanisms and control schemes. I figured making low-cost, easy construction 4" mecanum wheels would be a neat sub-project. Not being particularly mechanically inclined (which is partially why I'm doing this), I enlisted the help of my dad (squirrel).

The design went through a series of iterations, but stayed mostly the same. I planned on 6 rollers per wheel to keep costs as low as possible. At first, the center plate and "fingers" were made of 1/8" steel, because that's what we have laying around. The idea was to cut slots at 45 degrees on a chop saw and weld 1/2" strap into those slots. After a short time, it became apparent that 1/2" plywood could be used for the center plate and 1/4" for the fingers. This eliminated the need for welding (wood glue now) and made cutting out pieces much simpler (table saw).

I didn't have many ideas in the way of roller construction, but the robot we made a few years ago used wooden dowels trimmed down on a lathe, so that's what we're using for this. We also found that rubber stoppers are available in a variety of sizes at McMaster, so buying two sizes with slopes that approximate the curvature of the rollers might work too (and then we wouldn't have to wrap them with anything!).

The rollers are held on by tightening two 7/32" aluminum tubes of 1/4" length over a 3" #10 threaded steel rod that passes through each finger. Washers are placed between the tube and the finger, and nuts at each end are tightened to provide a very rigid, low-friction axle for the wooden rollers (see attachment).

The current issue I'm having is the nuts are just a little too big (or the rollers too small). I would love to hear other ideas for attaching the rollers, unless making them slightly larger is the best solution.

My dad says they'll take forever to make. He's planning on teaching me how to use the lathe so I can make the other forty-seven rollers.