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National Advisory Committee for Aeronautics, Technical Notes - An Impulse Electric Motor for Driving Recording Instruments

The chief purpose in'undertaking the development of this syn-
chronous motor was the creation of a very small, compact power
source, capable of driving the film drums of the recording air— _
craft instruments designed by the staff of the national Advisory
Committee for Aeronautics.

The working parts of the motor are few and simple. They con-
sist of four spool type fie1d_ooils, a reciprocating armature, a I
ratchet wheel and tw0'paw1s. The field coils, operating in pairs,
alternately pull the armature from one pair of pole faces to the
other.pair. This reciprocating motion is transmitted to the ratch—
et wheel through the two pawls, motion in either direction produc—
ing a positive advance of the wheel. Rotation of a very regular
character is thus secured.

The motor is 1 3/8 inches long, 1 5/16 inches wide and 7/8
inch high, with a volume of 1.43 cubuc inches, and a weight of
.165 pound (75 gms,). It produces approximately 6.0 x 10"5 HP,
with an efficiency of 1.0 per cent- The speed_range is from
O to 35 R.P.M¢, the torque being .234 pound-inch (269.6 g--Cm-)
the lower speeds with 8 volts applied.

Due to its small size and light weight, its inherent slow speed
and property of absolute synchronization, the motor is particularly
well adapted to aircraft instrument work. Application of this type
of power source may also be made to automatic recording instruments
of all kinds, to indicating devices requiring absolute precision,
of movement, and to remote control work.

The specific problem which was responsible for the development__
of this direct current synchronous motor, was that of driving the H__
film drum of an instrument called the sun hymograph.

The requirements of this instrument are fourefold: First, the
drive must be slow speed; second, the rotation must be uniform and
regular; third, the part of the drive attached to the instrument
must be small, compact and light in weight; and fourth, the connect-u
ing link between the instrument and airplane must be flexible.