So, I'm trying to build a bi-directional motor controller. The standard format for such a beast is the H-bridge. There are 5 essential states to a H-bridge: Freewheeling, forward, reverse, and braking to supply or ground.

It's simple enough and I've known this for a long time (it was shown to me as a young boy by a father's friend using a DPDT knife switch). What I think I've done is underestimated the importance of the braking modes (not something achieved with the DPDT switch). I'd heard before about braking in H-bridges before, having seen them in application notes, and listed as a feature in H-bridge driver semiconductors, but hadn't seen it in practice.

Seeing how useful it is, was an accident. I was testing one of the motors I have, and during an unpowered spin down... I knocked its terminals together. The result was immediate and obvious.

I presumed the amount of braking force applied when the terminals were shorted would be related to the amount of current the motor would generate. Since these were designed as motors, and not generators their generation ability wouldn't be much, and therefore braking by shorting the terminals would be minimal... I love to be surprised.