"Hopping" With tank style turning.

[Ryan Foley]

There are a couple ways to do this:
1) use less "grippy" wheels. Since the wheels will slide easier, it won't hop
2) widen your wheelbase. If a wheelbase uses 4 identical wheels like you have, and it is longer than wide, it will hop. Typically, robots that are wider than they are long will not have this problem. Note that for this purpose, you measure from where the contacts the floor.

At this point in the season, #1 would obviously be easier for you to do.

There may be other ways around this problem, but this is all I can think of off the top of my head.

This whitepaper discusses this problem and shows you how to fix it.

Good Luck!