pic: More fooling around with mecanum wheels

Just messing around again. Here is a 3" diameter mecanum wheel with a 2 speed gear box. The speeds would be about 6.4 and 12.7 fps. The wheel has 8 rollers, bearings in the wheel, gear bolted to the side, dead shaft. CAD says the weight of the assembly (with aluminum plates not lexan) is about 6 pounds. My conclusion: I don’t know if it would work or not but the 3" mecanum wheel looks really odd.

Yes, a three inch mecanum wheel would be a bit ridiculous, a wheel of any type smaller than 4 inches is rare in FRC.

On another note, you should consider how you are mounting these. Mecanum drives do weird things when any of the four wheels lifts off of the ground so some sort of suspension is recommended.

Yes - it’s not a serious proposal. Just got to thinking about it and wondered what it would look like.

Have you tried shifting with mech’s befor?

We did a mini-octocanum drive last year and had mecanums with fixed raised wheels for climbing the ramp in 2010. We’ve never done a shifting version. (The mini wheels were 2" diameter Colsons.)

What is mini-octocanum? Is it standard octocanum with smaller “tank” wheels?

Yes. Since we wanted a wide robot there wasn’t much room for the second set of wheels. We tucked 2" diameter Colson wheels in as close as possible to the 6" mecanum wheels.

Here is a picture of the module. It worked really well except for being rather heavy. (The frames were aluminum not Lexan.) If we did it again, we’d work on bringing the weight down.

What CAD software is this?

Personally, I am interested in what you did you color the bearings. I haven’t been able to make them look like the shiny metal bearings you have.

Very nice render!

We use Creo. I made the bearings chrome. The other parts are aluminum, steel, brass, plastic, etc. Creo has lots of material choices and then choices for each material. For example, under the aluminum choice you can pick brushed, anodized blue, anodized red, cast, matte, polished, satin or scratch. The room for rendering is set to glossy white plastic.

Tom, you’re the man. You make some really sweet models, even if you’re just fooling around with some of them.

If the wheels were 2.5" instead of 3", I’m not sure why this is infeasible at a first pass. I think this design would be robust enough for a FRC bot on a flat field under 2 conditions: 1.) The lexan that supports the outer edge of the dead axle were replaced with C-Channel and 2.) The robot frame only mounts to the C-Channel.

3"x1.5" C-channel with 0.2" leg thickness would work great. The added ounces of the Aluminum C-Channel would be offset by leaving the gearbox plates as polycarbonate. All robot impact forces resolve through the C-Channel, and the polycarbonate only needs to be strong enough to rigidly cantilever the CIM as shown.

*Hi Tom,

I’m interested in the rollers.

Could you post a spreadsheet (or a text file) of the roller contour profile (roller radius vs position along roller axis). Thanks.

I generated the profile in CAD. I took a 3" diameter circle and projected it onto a plane tipped at 45 degrees. Then I played with the roller center line to get a roller size that fit nicely. I set the width of the roller so that the end of one roller was in line with the start of the next roller.

Is this with Creo Parametric? How long did it take you to render this? As for the bearings, did you color them entirely chrome? Or did you color them any additional colors (for example, different faces different colors, etc).

It’s Creo Elements/Pro (Wildfire 5.0). I didn’t time the render but I believe it takes maybe 45 minutes or an hour. I do a draft render first that only takes a couple of minutes and if everything looks good I put all the settings to maximum for the final render. The bearings are just chrome but other parts have multiple colors. If you look closely at the nylock nuts you may be able to see the nylon inside the nut.

Amazing render, I’ve got an assembly of a transmission and I’ll try that chrome color to the bearings thanks!