With the Hurst high-torque motors a pause or "interrupt" causes them to reverse. These are (or were) available in various rpm versions but the speed was a function of the gearbox and thus not variable. To give you an idea of what Hurst meant by "high-torque" I bought two, one for the BZTS tubes and a second to drive the front standard of an Elwood 8x10 Enlarger. If you have ever seen one of these beasts you know that the bellows, standard, lens-board and lens add up to a significant amount of mass and the Hurst motors are still going strong after twenty years or so!
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