6 wheel center drop live axle custom sheet metal chassis (AL 5052 .090") with 10" pneumatic tires from Harbor Freight ($4.99 each).
We had custom hubs turned by a sponsor. #35 chain with axles placed with specific c-c distance so we didn't need tensioners. AndyMark Cimple Gearbox with 4 Cims geared for a free speed of 8.8 ft/sec.
No issues doing defenses as we could easily go over defenses. No observed damage on the chassis. Even survived a 3 foot fall off of our robot cart at one competition.
We went with 10" pneumatics given our experience in 2012 with the 4" tall center divider. That year we used 8" pneumatics and essentially couldn't get over the center divider or could with extreme difficultly. I am surprised that most 8" wheels had no issues going over the rock wall. I think the ramps had something to do with that which is something we didn't have on the center divider in 2012.
The team initially decided to go with a track drive. Luckily everyone was sold out in the first few days. We have never done a track drive and I wasn't too keen on doing our first one during build season.
Overall, a very good choice for us. Got us our first trip to Champs.
- Tom