there were cassette decks that had motors made by Robbins that were very efficient. as an experiment in braking force with one of these motors, i jumpered the power leads together and tried turning the shaft with a pair of pliers. either i wasn't able to get a good grip with the pliers or that shaft was super hard to turn (or maybe a bit of both). i know i couldn't turn it barehanded... and it was a small motor with a 1/8" dia spindle. without the jumper, the shaft would spin easily. the motor came out of a large data cassette drive that used standard c-30 cassettes to store data.