Moment of inertia and turning performance

[IKE]

Originally Posted by JesseK

Personally I like to drive the full-weight robot at full speed into a brick wall while it has bumpers on. Driving it in at various angles so the corners hit also helps.

Why? Usually a frame stays square "just fine" until an impact. Then things can get bent out of shape.

You might be missing the point, the frame is not "bent", but bends torsionally under load, and then returns to flat. When this occurs, diagonal corners touch down and diagonal corners lift. X=touching, 0=not touching:
X X O
O X X
This reaction effective turns somwhere between a long and a short wheelbase, and makes turinging more difficult.
In order to counteract this, teams will often add more "drop" to the center wheel. As the CG Height increases, this increases rock which can cause the center of rotation to oscillate between front of center wheels and behind of center wheels. The stiffness of the wheel/tires, carpet then act like a spring. The softer the spring, the more displacement, which in turn will equate to more energy (E=1/2KX^2 where as F=KX decrease K, and X increases proportionally in which energy increase due to the X^2 term).
This is why buck bobble is more prevalent in pneumatic tire chassis.