Well I guess we don’t have a totally great answer for why except that when we used them on the front the robot steered ‘about’ the rear wheels which made it hard to grab the goals last year.
When they were on the rear wheels the robot spun about the front wheels similar to a fork truck.
We also tried them on all four wheels and the robot spun about its center but it didn’t have as much pushing force as dedicated traction wheels on two of the four.
Oh, I think I get it now, those white roller thingys alleviate the side friction problem. How did you guys go about manufacturing this and what exact materials did you use.
Matt, thanks for the better picture. I am sure I have one some where but that was the best I had at work.
Construction… The large wheels consist of a sandwich of 2 aluminum pieces in which areas are relieved to hold a small axle for the white rollers to turn on. The rollers had slots cut in them for the o rings and then the o rings were glued in place. Each drive module had two assemblies because we found that the rollers were not in contact with the floor long enough to grab. Two assemblies next to each other but offset, allowed at least one roller to be in contact with the floor at all times. The rear drive set used normal wheels and performed the drive for steering. Note that a normal tank style drive with this arrangement allowed responsive steering without the side friction problems.
This robot was for the ramp competition and the drive was strong enough that we were able to drive around with another robot on our back and drive across the ramp.
We have discussed various designs to replace the roller/o-ring arrangement but have not used this design again. A roller made from aluminum with some kind of tooth cut in the surface would be ideal though.
I should mention that our mechanical engineer, Raul, is the one who is responsible for this design. It was in direct response to the electrical team’s research on high current demands in tank drive systems.
Just a few more hours…
Here is a design for a trick wheel that we used on our 2000 robot.
http://www.theforumisdown.com/uploadfiles/1102/trick%20wheel%201.jpg
(copy & paste the link)
edit: fixed link
edit#2:fixed url parse
*Originally posted by D. Gregory *
**Oh, I think I get it now, those white roller thingys alleviate the side friction problem. How did you guys go about manufacturing this and what exact materials did you use. **
Look in the white papers under team 226 crab drive for the plans on how to make the plates for the omni-wheels.
*Originally posted by Matt Reiland *
**Look in the white papers under team 226 crab drive for the plans on how to make the plates for the omni-wheels. **
For what it’s worth, I’ve ‘adapted’ those omniwheels into an Autodesk Inventor assembly (R5). I changed the bolt hole pattern around shaft so it would meet my preferences. Anyone with a little working knowledge of Inventor can change that easily enough.
Forgive me, Matt, if I bastardized your design. If I did, please let me know. I want to know the wheels will work if we decide to use them 
(The file is a little too large to be an attachment. If you’re interested in it, PM me and we’ll figure out some way of getting it to you. It’s really nothing all that exciting, though. It took me about 20 minutes to make.)
*Originally posted by M. Krass *
**
Forgive me, Matt, if I bastardized your design. If I did, please let me know. I want to know the wheels will work if we decide to use them
Not my design M 
it was lifted from Wildstang and I think it is yours to do with as you desire.
*Originally posted by Matt Reiland *
**Not my design M
Well, I lifted the design from your team’s CAD drawings in the White Papers section. So, thanks for those, and thanks to Wildstang for making them in the first place, and thanks to cavemen for inventing the wheel
I managed to upload it to FTP.
http://www.magenet.com/~imagination/Inventor/OmniWheel_INV5.zip