Team 931 Omniwheels

[bheller]

Omniwheel Render (http://userfs.cec.wustl.edu/~bdh4/Omni/Isometric.jpg)
Omniwheel Picture (http://userfs.cec.wustl.edu/~bdh4/Omni/Omni%20Reality%20Iso.jpg)

Click on the above links to both a render and actual picture of Team 931's new omniwheels. The outer plates were waterjetted and milled by a sponsor, but the rest was student-fabricated, including the shafts, hubs, spacers, and rollers. These wheels are a drop-in replacement for the 9" Skyway wheels. We used 60A durometer urethane for the rollers. It's extremely flexible stuff -a pain to machine but worth it due to the excellent traction. The weight of the robot actually deflects the profile of the rollers so much at the roller edges that the wheel profile very closely approximates a circle.

So we installed them on the robot the other day, and they worked _too_ well! Think about it - with an omniwheel you essentially have casters when the robot's turning. The rotational inertia causes the robot to keep spinning when you lay off the stick, just like casters, causing overshoot. We're pursuing a gyro (ADXRS series) to fix this. The robot turns MUCH faster now.

Many thanks go to the Technokats, whose Trick Wheel design inspired these wheels. At the end of the season, I'll post a White Paper on the design, with inventor files, .dxfs and bill of materials.

Whaddaya think?

Brandon Heller
Team 931 Mentor
Team 449 Alum

[pras870]

Wow, very very nice.

[KyleGilbert45]

Very Nice Trick Wheels!

It's always nice to know that something you worked on and helped build inspired someone to create something of the same magnitude if not better.

[Yan Wang]

Heh, those look uber familiar... like two of ours from last year, offset and with weight reduction.

How large are they? Based on the actual picture, I can't tell.

[Winged Wonder]

those are cool!

[bheller]

Heh, those look uber familiar... like two of ours from last year, offset and with weight reduction.

How large are they? Based on the actual picture, I can't tell.

The OD is 9", the hub diameter is 2", and each roller is 1" diameter x 1.5"L.

Weight is 2.7lbs vs ~2.4lbs for the Skyway Bead-lok, but could be brought down to about 1.7lbs by replacing Aluminum with Polycarbonate. It'd look like this (http://userfs.cec.wustl.edu/~bdh4/Omni/Lexan.jpg). These wheels are BEEFY, but the pictures don't show it. The roller axle size was increased from the Technokats design.

I wasn't involved with FIRST last year and didn't see your robot. Do you have any pictures? I checked your team's website and didn't see any from 2003.

[Yan Wang]

Lol, that's the exact same dimensions of ours...

We used Lexan instead of Aluminum, but we did use 60A urethane just like you.

Here's the pic/thread: http://www.chiefdelphi.com/forums/showthread.php?t=24526&highlight=639+2003+omniwheel

[bheller]

Lol, that's the exact same dimensions of ours...

We used Lexan instead of Aluminum, but we did use 60A urethane just like you.

Here's the pic/thread: http://www.chiefdelphi.com/forums/showthread.php?t=24526&highlight=639+2003+omniwheel

I see. The main differences between our designs is that mine uses an external milled slot (like 45) for the axles, so that we can remove any wheel without taking the wheel apart, and has two rows of rollers.

I did most of the urethane work. If you set up a jig, you can cut very accurate rollers. The stuff is so flexible that the cutting edge of a drill bit tends not to bite in. The holes we drilled with a .1875 drill bit actually came out more like .16. That's a lot of stretch! Originally the plan was to CNC the urethane to an exact profile. Liquid Nitrogen can be used to chill urethane to the point that it acts like a much harder-durometer urethane. I was all set to use that, but then the urethane arrived and we realized it was so flexible that the weight of the robot would compress it to a nearly circular profile.