[Tom Line]

This appears to be what we tried - 4 wheel skid steer omnis with two wheels perpendicular to those 4 to provide translation (6 total).

Unfortunately what we found was that no matter how carefully we aligned the bottom of the wheels, we either had too much weight on the outsides and not enough sideways traction, or the translate wheels were down too much and one side of the tank drive was off the ground.

It looked like this:

___________
|x....xxx....x|
|x............x|
|...............|
|...............|
|x............x|
|x....xxx....x|

x's are the wheels