Spies Among Us: How to Stop the Spies

A hoist of light weight e.g., 10 lbs., and high capacity, e.g., 500 lbs., with infinitely variable speed and holding characteristics. A sprocket engaged with a roller chain is driven through a multiple-stage spur gear reduction train by a high-speed universal reversible electric motor energized through a modified silicon control rectifier. The reduction gears are of high tensile alloy steel, mounted on roller bearings to give an efficient drive, and the gear reduction is of such high ratio as to give the gear train a high degree of irreversibility. One-way drag braking opposes load-lowering movement of the high-speed and of the gear train, and interacts with the irreversibility to positively hold suspended loads and require the motor to drive the load down as well as up. This combines with the SCR control of the high-speed motor to give positive variable-speed lifting, lowering, and holding control of the rated load.