Brushless dc motor operates as a commutator in a vacuum environment with high efficiency and long life. Because of its excellent response time, it can be used in the servomechanism field

Studer, P. A.

English

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August 1966	 Brief 66-10355 
NASA TECH BRIEF 
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program and to encourage their commercial application. Copies are available to the public from 
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Brushless DC Motor Has High Efficiency, Long Life 
Switching Transistor 	
1 
DC Supply 
Light Source
Switching Transistor 
ght Shield 
The problem:	 90 degrees. It is the function of the commutator to 
Brush life of conventional carbon brush commuta- 	 apply the external power to the motor windings in 
tors is measured in minutes when operated in a	 such a manner as to maintain this angle for all posi-
vacuum environment.	 tions of the rotating member. Physically, this motor 
The solution:	 is an inversion of a conventional dc motor in that the 
Development of a brushless dc motor with true dc 	 rotor is a permanent magnet and the stator is wound 
motor characteristics.	 (in effect a stationary armature). Attached to the 
How its done:	 end of the rotor, opposite the drive end, is a small 
The principle of operation of this brushless motor 	 light source within a shield, in which a small aperture 
is identical to that of the conventional dc motor. A
	
has been cut. In the plane of sweep of this aperture 
torque is produced when two magnetic fields are 	 are six photodiodes spaced at equidistant points, 
established with a relative angle between them. This 	 60 degrees apart. When the dc supply current is ap-
torque reaches a maximum when the relative angle is	 plied, a portion of the light strikes one of the six 
(continued overleaf) 
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photodiodes. The illuminated photodiode produces a 
current which is amplified and , fed to the bases of a 
pair of switching transistors. These transistors apply 
the power supply current to the appropriate points in 
time on the ring-type stator (stationary armature) 
winding. This produces a magnetic field at the proper 
angle in relation to rotor position and a turning 
force is imparted to the rotor. As the rotor turns, 
the light source, shining through the shield aperture, 
illuminates the other five photodiodes in turn, and 
the above process is repeated at each 60 degrees 
around the solid state commutator. The detecting de-
vices are silicon photodiodes with rise time of 1.5 
microseconds and fall time of 15 microseconds, af-
fording a system capable of speeds well in excess of 
the design speed of 3,000 rpm.
Notes: 
1. This motor, because of its excellent response time, 
has considerable potential for use in the servo-
mechanism field. 
2. The motor has an efficiency of 50 percent. This 
could well be increased to 70 to 80 percent using 
the latest magnetic alloys and winding techniques. 
3. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B66-10355 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546.
Source: Philip A. Studer 
(GSFC-181) 
Brief 66-10355	 Category 01


Brushless dc motor has high efficiency, long life

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