Potentiometer: Podolsky Roller-Contact Unit in a Moulded Casing

Podolsky's variable resistor (Wirt Company, US 2,060,114, 1936). The carbon strip is bent into a ring inside a moulded casing, and instead of a sliding wiper a small roller runs round it. A coil spring presses the roller out against the strip with even pressure in every position, even over slight irregularities. The patent gives no sizes; the parts are named by what they do. The picture: the patent's drawing (Figs. 8 and 9).