We used belts really effectively this year. You have to take some care when designing the system but it can be done simply and effectively. We got our parts from
www.sdp-si.com. They have a great design assistant to know what you need. You should use a timing belt, V belt or friction belts require friction and extra systems. The key to the design is keeping some tension, but no more consideration that if you were using chain.
Most suppliers will have how to choose the size and center distances of your belt. It could be a calculator or a simple formula. Any mechanical design book should have it as well if you start looking around.
Know how much power, what and how many motors, you are going to be running with the system and figure out a max torque that you could experience. Based on that torque and the pulley you use you can figure out the force in the belt. This will tell you the belt width and what type of braid you should have, kevlar, steel, glass, etc. Make sure you design in a safety factor, you want your drive train to work all the time right, 2 should be plenty maybe even 1.5. Your experience will allow you to choose what is best for you.
We did this and figured on a 3/8 timing belt. This was for 2 cims and 1 fisher price on each side. We had to replace the belt once during build testing because our cast urethane fell of and got mingled in with the pulley and caused a rip. After AZ, Boston regionals, Battlecry, Beantown Blitz, Mayhem at Merrimack, and several demonstrations on various surfaces (Brick, dirt, not carpet) we finally have to change out the belt on our drivetrain.
So with some care and consideration when initially designing you can choose what you want and not have to worry about chain, grease, noise and most importantly, 4-5 lbs of weight (depending on the chain you use)
If you want to know more I think I have an excel spreadsheet somewhere of what we did and I can send it to you. I'll have to find it though.