Another way to balance a table
We need three mini-vehicles.
If you use only two mini-vehicles around a circular table, then it's possible for
the table to tilt in such a way that the mini-vehicles
can't counterbalance instantly.
A microprocessor converts the three sensed pressures
into a set of three (positive or negative) voltages to drive
the respective mini-vehicles.
Part of the logic is to keep the mini-vehicles spread apart from each other around the perimeter so that they can respond quickly to a push in any direction. You can see the principle in the java applet to the right, which shows a schematic top view. Try dragging the blue "weight" around with your mouse, and watch the three red mini-vehicles run around the perimeter so as to counterbalance.