This is why we use 12 volt drills with their battery minus their motors. They come with controls for reversible polarity and variable voltage. Just add fuses and connectors.
Who needs a (cordless) Dremel when you have two robot batteries and a 775Pro? 
Use a large(as in physical size) main breaker/power switch so it can be turned off quickly and easily in the event of an emergency. An E-stop button may be a good option, but the low priced ones can only handle about 10 amps, so I wouldn’t use it for large motors.
Just to add a little to this discussion…
Stall current is by definition, the current a motor draws when power is applied but the motor is not turning. (Start satisfies this definition.) The large CIM is rated at 131 amps stall.
As stated, no breaker is designed to protect a motor. It is designed to protect the wiring in an electrical failure. That is why the electrical rules relate breaker size to wire size.
Most pots are in the 1/4 to 1 watt rating. At 100 amps, that pot could be asked to dissipate 80+ watts when in series with a CIM at half speed.
The drill option stated in several places, gives a lot of advantages including reversing, variable speed and it likely also has internal over current protection.
An alternative is to use an inline fuse holder designed for the maxi-fuse 40 size when wiring to a robot battery. The inline circuit protection should be placed as close to the robot battery as possible to protect the wiring and load from heat and fire. Use a 40 amp breaker in place of the fuse. The main breaker can also be used but is harder to insulate and protect.