TechDante:
Have you found out what the stall current and running current for your motors are? Until you know that information, you can't size and select (or build) an appropriate motor driver h-bridge for them.
For example, I have some small hobby DC motors, which pull about 250 mA running. If I stall them out, they pull around 1.2-1.5A, or 4-5 times their running current. Some DC motors will have even greater stall currents (engine starter motors, for instance, can pull a few hundred amps).
Have you measured and verified the running current for the motors? Is it truely about 5 amps? If so, figure out the stall current - the difficulty here will be doing so without causing a fire or smoking the motor. If you can find the manufacturers specs for the motor, that would be best. Otherwise, inline a fuse holder to the motor connections, and use a car battery (or starter/charger set). Put in a 5 amp fuse, and stall the motor out (easiest way is to remove it from the gearbox, mount it securely to a bench, then clamp the shaft with a pair of vice-grips so that the direction of spin forces the pliers against the bench so the shaft can't turn) - you'll only want to "pulse" this - inline your meter (hook it up for high amp measurements - meters typically have a different jack for the positive probe for high-amp testing - otherwise you'll blow the meter). You don't want to apply the power too long, because if the fuse fails to blow, you burn out the motor or something else. If you can figure out a way to make a "slip clutch", that would be better (maybe vice grips around a section of hose slipped over the shaft, and tightened down so that the shaft can still slip some).
Once you know both currents, then you can find out what size of controller you want to use; really, you are looking for a "power chair motor controller", because that is what was used to control them originally. Mind you that these controllers are anything but inexpensive.
You might try this site for some more information:
I can almost guarantee you that "Sabertooth" dual motor driver isn't going to work out for the motors, but you will need to first find out what current the motors draw while running and at stall, before you can know for sure.
Good luck.
