I'd agree with the 'hockey pucks'. We used to have several variable speed drives in the plant that used them. One of my jobs on the annual PM was to use a calibrated gauge to make sure the bars holding them in place were tight enough that they bowed the required distance. I was always just a bit netvous when I had to troubleshoot around those things. I'm sure 'letting the smoke out' of one would not be a good experience.
