Motor Driven Potentiometer

[internal motor]
Motor, Low Inertia
Type 901
Ser. No. 5400
Volts 6 D.C.
Electro Methods Ltd
Made in England

The Electro-Methods Ltd. Low Inertia Motor was copied from the original German Mess Motor, one of the technology/patent items taken from Germany at the end of World War II. The original German Mess Motor was used as an integrator in wartime German autopilots and missile analogue computers.

In the Mk13 autopilot (as used on the Lightning) it was chosen as a low inertia, low current, low friction servo motor which could be driven from a small magnetic amplifier. The Mess motor drives a potentiometer and an Elliott AC pick-off via a gearbox. There were two such units in the Mk13, only one having the AC pick-off. They were used to follow-up attitude from a Master Reference Gyro (later Sperry) to give the zero reference for bank angle and pitch angle attitude lock. The unit with the AC pick-off was the reference for the height-lock required for the automatic approach coupling.

The Mess Motor was also used as an integrator in the analogue computer for the inertial navigational system for the Redcheeks guided bomb c. 1951. A DC voltage proportional to acceleration was derived from an accelerometer and applied to the input of a thermionic valve integrator. The output of the valve integrator, proportional to velocity, was applied through a cathode follower low-impedance amplifier to the Mess motor. Since the speed of the motor was proportional to the applied voltage, the total rotation was proportional to distance. The Mess motor drove a potentiometer via a gearbox, the output from the potentiometer was applied to the autopilot.

This example is an early prototype used in development at Borehamwood, Herts, Research Laboratories of Elliott Bros (London) Ltd.
This item was part of the original Elliott Collection Ref: 2010