OK, let's try something else...
What do you want this to do?
What kind of payload (12v car battery, or 7.2v RC car battery pack? BIG robot arm or just a sensor array?)
What kind of terrain?
Radio controlled? Or auto mode all the way?
Size? (Just big enough, or room to play with other add-ons?)
Use? (Just to test sensors, or future battle bot frame?)
Speed?
Complexity? (Sounds like you want simple as possible, with bandsaw fabracation only.)
Cost? (Can we spend $35,000?)
Etc...
SO, if you could describe what you want this to do, exactly and to as much detail as possible, I bet people here could help you come up with a design good for you.
Tell us as MUCH as possible. Even if it seems obvious to you. I'm not so smart most of the time, so you'll have to spell it out for me.
This could be fun!