Heavy-Duty Battery-Powered Electric Drill: Riley & Elligson, 1965

Robert H. Riley Jr. and Daniel M. Elligson of Black & Decker patented a cordless drill in 1965, US 3,213,305, with about the torque of a corded half-inch drill, for contractors and line workers. A permanent-magnet DC motor drives the chuck through a two-speed gearbox. Two hollow side handles each hold a slide-out pack of rechargeable nickel-cadmium or silver-cadmium cells, wired in series with the motor and a trigger switch. Their working model had 18 silver-cadmium cells, about 25 volts in all, and gave 550 rpm in high and 225 rpm with 28 foot-pounds of torque in low. The low voltage made it safe in ordinarily hazardous conditions, such as boat maintenance and repair.