Saw this on TV on the QI show. Just had to try it out. I wrongly called it a monopole motor as it is (apparently) correctly called a homopolar motor. The design was actually the first form on electric motor, and many uses were extensively investigated in the late 19th Century, but for various reasons gave way to the more common iron core, brushed and brushless designs which tend to be more high voltage, but less amperage motors. That is compared to the low voltage but high current homopolar design. It is because of the high current abilities of the homopolar design that railguns use them due to the high amperage being able to accelerate projectiles more rapidly and faster than the lower amperage designs.