Well, its a bit late but I just had this random, interesting idea for drivetrain building; no idea if it’s legal though. My team just ran a kiwi omnidrive, which worked beautifully IMHO with correct load balancing (Our last 3 games, we had no practice with the properly setup drivetrain). Meh, I know we could have bridged too with that, just had no practice.
Anyways, what I was thinking was adding a fourth wheel (or duo), traction type, in the center of the bot. It would be raised/lowered by a pneumatic piston connected to the front bumper (ideally jutting out a bit from the main frame structure, via frame perimeter extension sitting on top). The idea is that omni drives inherently can’t push as hard as tank; this would enable tank drive on that platform with two powered rear wheels by just putting them down with the piston to a set distance via reed switch to engage them. Specifically with pushing, you could hyperextend the piston when holding ground. What I believe theoretically happens is they apply pressure to the angled piston when pushing it, which just forces the traction wheels more into the ground to make their push harder. Only drawback is you might have the bumper jacked up a bit at times, and I dunno, is that legal (assyme the bumper height is not exceeding the bumper zone)? Technically you do still have a wheel in contact with the ground, not just a stick.
We used two cylinders to pneumatically lift our robot up about 15 inches to land on top of and drop the bridge this past weekend in Hawaii. The cylinders pushed a wheelie bar capped with wood ends from the bottom of our frame. It pivoted from just behind the front bumper. One of the latest updates allow you to temporarily violate the bumber zone to cross the bump or to get on a bridge. These were the only two exceptions and we were warned not to wheelie too far from the bridge to avoid a penalty. We thought of using it on the bridge to drive up onto a partner but I don’t think that would be legal under the exceptions made in the update. You can always run it by the head ref in practice. BTW, it worked like a charm everytime!
Yes, this is a perfectly legal method of a drive system. You can see very good implementationson both 148’s and 217’s bots from 2010, of a slightly different drivetrain, where all the wheels pivot down, the sides pivoting down onto treads, and the center wheels being pivoting omnis. While it is very maneuverable yet still being able to push other robots, it is slightly complicated and it does use many motors.
While not quite on the scale you’re looking for, you can also see this type of acuation on 1625’s Logomotion robot, with their side moving 10 wheel lobster drive, in which they are a standard 6 wheel drive, but then also have 4 perpendicular wheels (2 front and 2 back) which come down and lift their 6 wheels off the ground so they can translate sideways.
I’ll get some photos this weekend of our robot, we have a 6 wheel drive, where the center wheels are mounted on pneumatic cylinders to retract the wheels when crossing the bump and balancing on the bridge.
Alternatives you may want to look around CD for are octacanum (Madison’s made a lot of great posts detailing how you can make one) and jump drive (a.k.a. jester drive).
