Re: Mecanum Wheels?
 

We used mecanum wheels that were very succesful.. There are a couple of flaws.
1. If they get bent out of shape you need to use another one.
2. They are not cheap.
http://www.team1708.org/content.agent?page_name=Video
This is our website with a couple of videos on our wheels.

They have great maneuverability.!!!!though

Re: Mecanum Wheels?
 

Note that it is traction that COG effects more than anything. If COG is closer to a particular wheel, that wheel will get more traction and therefore more pushing force against the carpet. Since mecanum design is all about vectors that cancel each other out, it is imperative the weight be distributed evenly. Simple suspensions may help even things out, but movable weights and/or adjustable motors are probably simpler, lighter, and less exepensive.

After seeing a new concept of strafing that 1565 has put together this year, I am now not so impressed with mecanum wheels. They have great advantages such as simplicity to mount. However they do have their inherent flaws, such as a certain % of your power is lost due to power vectors that cancel each other out. This particular one is a doozy for me, and the new 1565 modification I have in mind fixes this and even omni drive's difficulties in climbing ramps.

If you'd like to prototype mecanum before next year, the summer is the time to start. I'd take June & July to do research on parts, prices, and weight, then take Inventor or Solidworks and work out a frame & mounts. By the time the school opens in the Fall, see if your team has the resources to do a prototype (note that the parts & code you build now may or may not be legal to use in 2009) then I would suggest building the prototype. I would also note that the FRC controller is changing in 2009 unless something changes in FIRST's plans, therefore any code you write now will have to be modified in the build season anyways.

If you require that your team use mecanum next year, you might be in a world of hurt when you go to integrate all of the pieces onto your bot. It is far easier to design things to integrate together from the start than to have an unchangable piece that every other piece must fit around. Frame modifications come to mind as well as manipulator mounts. That's just my .02 for that subject though.

Re: Mecanum Wheels?
 

I've had some experience with Mecanum drivetrains, I'll be inspecting at the MN regional, feel free to stop by and talk to me (Friday or Saturday, after everyone is done inspecting).

As far as ramps go, the only problem we had last year with ramps was not driving sideways off them if there were no sides. We solved that with a switch on the joystick that disabled the strafing, so that the driver didn't have to keep the joystick perfectly straight while going up the ramp. The ability to line up on the ramp was priceless, then just pull the trigger and drive straight up. With a wheel diameter in the range that is useable on a FRC bot, a suspension is almost mandatory. Last year I was able to drive the robot over 3/4" thick obstacles on the floor at full speed when practicing.

Most of the pros and cons have been discussed pretty well in this thread. My advice if you are serious about considering a drivetrain of this sort is to get some help from people who have done it, and to prototype something over the summer to experiment with. Your programmers will appreciate that... We were able to make some plastic wheels on a rapid prototype machine a couple of years ago that we put on a Vex chassis. That let us decide that we could make it work on a full size FRC robot.

And always be prepared to change your mind and plans when you find out the game and rules for next year.