[PAR_WIG1350]

4WD only "jumps" when all 4 wheels have a lot of traction (side friction) switching 2 wheels to slick wheels will fix this.

Also, drop-center 6wd is not true 6wd because you really only have 4 wheels on the ground for most of the time. 6wd doesn't give you more maneuverability, a shorter wheelbase does:

If you wanted to turn a robot about its own axis (the center of the wheelbase) easily, draw a circle that is centered on the axis and intersects each pair of wheels at the wheels, do this for each set of wheels. The closer the wheel is to being tangent to that circle, easier it will be to turn. The circles drawn must be concentric for this to work. Using this method, it can be seen that wheelbases that are wider than they are long will have wheels closer to tangent than longer wheel bases.

Now, change the center of the circles to the center of the force applied by the wheels during the turn. Now, the higher traction wheels should be closer to tangent than the lower traction wheels, this is good. lower traction wheels can slide sideways more than high traction wheels. If you find your drive train, when drawn out with this method, has high traction wheels placed really far off line with the tangent line at the point of intersection, it might not be a good wheel choice for that location.

Edit: I don't think this works well (at all) with swerve, mecanum, or holonomic drive trains