Back in the days when I first saw Bally's Who Dunnit around mid-90s, I wondered if the slot machine thing under its playfield was real. Only 5 or so years later from I got to take Who Dunnit apart to repair the said slot machine and sure enough, this stepper motor driven take is apparently how the slot machines did it too before they all got replaced with TFT screens. I've always wondered if Williams' slot machine department had anything to do with this mechanism.

Technically it's simple, a stepper motor and optical home switch. The game spins them all couple of full rounds during the boot, during which I assume it counts how many steps are needed for full revolution and then knowing how many steps are needed until the next slot symbol. Mine is lucky, it has just one aftermarket motor so far, the rightmost got completely fried.

The game doesn't really need the reels, the slots are 100% software so it'll still give the prizes even if the reels don't move and they're emulated on the TFT.