How to Implement Primary/Secondary relationship for motor speed.
The first question is analog or Digital motor feedback.
What is 'Primary/Secondary relationship'?
I'd expect the digital approach to be more accurate, but you will need to decide your own trade-off between how well it works and how easy it is to implement.
We prefer that you fuse the motors rather than the battery leads, or if for safety reasons you need to fuse the battery that you do it at a much higher current than the motors. The reason is this:Because Sabertooth is a regenerative driver, it relies on having a battery to put regenerated energy back into when you command a stop (and at other times). If you draw enough power to blow a battery fuse, all of a sudden the Sabertooth has nowhere to put the energy. It will see the fault, though, and try to stop the motor. It doesn't, however, have anywhere to put the energy (the mechanical energy of the vehicle and the electrical energy carried in the windings and the caps). So blowing a battery fuse will sometimes kill the driver -- which we would replace under warranty, but it's still annoying for all parties. The better way to do it is to fuse the motor leads. If a motor fuse blows, the motor will freewheel, the Sabertooth will sit there contentedly, and the only thing you will have to replace is the fuse. A very large fuse (100 amps) on the battery lead will protect the wiring in the event of a battery lead short or motor driver failure.
Are the motors just two lead DC motors, not brushless? If so, it seems to me you only need to open one lead with an E-stop. Please correct me if I'm wrong.