High torque machines for power hand tool applications

Power hand tool applications typically require a high output torque at modest speed. The product must be light, small and ergonomically designed. Forced air cooled DC motors or universal motors are typically used in combination with a step down gear box to achieve the required torque. This paper reports on some research which is seeking to produce better systems by producing very high torque density electrical machines. The work has sought to achieve this by using a combination of new materials, including both rare earth magnets and powdered iron, and novel topologies of machine. Two machines have been built: one uses conventional laminated construction for a radial field machine, the other uses powdered iron for a claw pole armature machine. Both machines contain a number of novel features; this paper gives the rationale behind each design and comprehensive test results thereby comparing their performance.