The other end of the ribbon cable is a quick assembly of two 5K potentiometers. The Sabertooth controller has two inputs that can be configured in many ways, but I've picked the basic analog mode. In this mode the controller reads voltage levels and determines what to do.
It can work two ways: individual motor control, or mixed. With individual motor control, each controller runs one motor. For the two sides, 2.5 volts has no motion, while higher and lower voltages move the motor forward or reverse. The two motors run completely independently.
In mixing mode, one control is steering while the other is forward or reverse. The Sabertooth figures out what you're trying to do and controls both motors accordingly.
I confirmed the controller worked as expected with the robot up on blocks, then dropped it to the ground and bolted on a plywood platform.
Of course, I had to take it for a ride! It was hard to control, and even keeping at a slow speed I bumped a few things in the garage. The independant motor controls were not intuitive, especially when they were two random controls held in my hand.
The controls were very sensitive, but I managed to make trips forward 15 feet, back up and turn around a few times. I switched over to "mixed" mode and it became much easier ... more car-like with steering and power.
This thing will do some serious damage if it runs loose ... it's heavy and feels like it could go pretty fast.
Eventually I'm going to hook up an Arduino controller, but first I'm going to work on a better set of controls and take it on a trip outside.