Omniwheels - how?

[Guy Davidson]

Now that FIRST season is over (at least for us), it's the time to look into fun side projects. I started looking into building something (in my case, a motorzied chair on wheels), and I'm thinking about using omniwheels. And then I realized, I have no idea how they work. I know that the system invloves a wheel, with another set of wheels on it instead of a thread (or something like that), but how exactly does it work? I couldn't find any good explanation here via search, nor could I find any in google.
Thanks,
Sumadin

[Dan Petrovic]

There are the regular wheels, and then there is a series of rollers rotated 90 degrees from the original wheel. Depending on what type material of rollers you use, you can get foward traction and still have an easy turning capability.

If your drive system is made of all omni-wheels, then you'll be pushed to the side really easily.

There is a drive system called "holonomic drive" where the omni-wheels in the corners are rotated 45 degrees from the drive base. Each wheel will have to be individually driven by separated motors. Depending on which way the wheels are being driven, you can strafe and drive in a circle while facing the same way. This is an omni-directional drive.

[irishninja]

Omni Wheels are wheels with little rollers around the edge. If you've ever seen a roller hockey puck you know what I'm talking about. The rollers do not reduce friction, the just allow the wheel to have wheels on it so it can move sideways easily. They allow for easy manuevaribility and turning due to the relative massive loss in friction.

So you have a wheel and then all around the rim are much smaller wheels, really rollers, that have a motion range perpendicular to the of a normal wheel, making it easier to move about, but losing traction while your at. I know vex has omni wheels that are super cheap and easy to fool around with, just so you get the concept. Hoep ive been a help

http://www.andymark.biz/plastic-omni.htm

[Daniel Morse]

213 used 45 degree omni wheel setup on our base to obtain a holonomic drive. Take a look at the photo attached to see the base. This allows us a full range of motion including rotation, linear motion (side to side), and a combination of the two in competition, which was extremely useful. The downside to holonomic base is the velocity that you lose to the rollers while moving in a motion such as forward, backward, or side to side due to the principles of how it works. Also, as was stated above, it is very easy to push the robot. For our team to approach this problem, we attached Kornylak omni wheels to a custom drive shaft and attached that to the KOP gearbox. The system is remarkably simple, and works very well. I would suggest that you begin exploring omni wheels on a simple premise like this, so that you develop an understanding of how they work. I also suggest looking at Kornylak to provide omni wheels, we used them in our robot and they performed decently well (except they shattered a few rollers if you tried to go up the ramp with them). Its a heck of a lot easier than making your own.