[Mr V]

You really asked 2 questions so I'll break it up.

The reason you don't need the load (resistor) to make the motor into a brake. Spinning the motor "backwards" turns it into a generator. The polarity of the output is such that it makes the motor want to turn in the "forward" direction or provide resistance to being back driven. This is the exact same method method used by the motor controllers in the brake mode, no resistance is involved other than that of the motor windings and the nominal connection resistance.

The reason it won't burn up the motor is that the output voltage and thus current is proportional to the speed of the "generator". The resistive or braking force is proportional to the input voltage. So the faster it turns the more braking force it generates, meaning that it will reach an equilibrium and fall at a constant velocity. The caveat is that if you were to spin the motor faster than it's free speed at its rated voltage, for any length of time you could harm the motor. However to do so would require a load greater than the motor's capacity.

On our minibot in brake mode it takes about 3X as long to come down the pole as to go up.

We initially used the three way "common household" sw but in the interest of weight savings we went to the limit sw. It required a little more polycarb to make a lever system that allowed the wheels/motors closing to turn it on but still latch in the off/brake position. The extra sq" or 2 of pc was more than offset by the weight savings of the micro sw.

The wiring is very similar to the three way. The com term goes to the motor terminal you want (+) for up. If you want the sw depressed to be the "on" state connect the NC terminal to the motor up (-) and B-, the NO terminal to B+.