Follower drives using alloy magnets

Butt-ended follower drives have been constructed in which each member consists of a mild steel disc on which a number of equally spaced rectangular or trapezium shaped blocks of permanent magnet alloy are arranged. A drive consists of two such similar assemblies, each magnetized with alternate N and S poles. Variations in the alloy and geometry have been made. The maximum torque that can be developed has been measured with a strain gauge transducer. The torques are greater than those that can be produced within the same diameter by ferrite magnets. A theory derived by Wullkopf for ferrite drives is reasonably accurate for high coercivity alloy assemblies. The influence of attempting to drive through a metallic partition is excess load on the motor rather than loss of transmitted torque. However, high resistivity partitions of austenitic stainless steel or Nimonic alloys are satisfactory.