18.104.22.168 Stray field reduction. - To reduce the stray magnetic field the motor shall incorporate
(a) Stray magnetic fields caused by electrical circuits shall be kept to a minimum
by making the area of electrical current loops as small as possible and
arranging adjacent loops so that their fields will be in opposition. Current
loops shall enclose no magnetic material unless essential for proper per-
formance of equipment. All motor windings and connections shall be
balanced for ampere-turns around the shaft to eliminate stray fields insofar
as possible. Each circuit which makes even part of a turn around the
machine shall return on itself back to the starting point, with conductors
for the forward and reverse currents arranged at the same end of the machine
and as close as adequate insulation permits. All connections shall be as short
(b) Brush rings shall be complete rings of unifomn resistance throughout.
(c) Leads to the positive and negative brush rings shall be located as close together as
22.214.171.124 Nonmagnetic motors. -
Nonmagnetic motors, when specified (see 6. 2), shall meet the
following additional requirements:
126.96.36.199.1 Design. - The design of the motors shall be as follows:
(a) Motor shall have not less than four main field poles.
(b) The number of interpoles shall be the same as the number of main field poles.
(c) The number of turns in any field pole winding (shunt, series, commutating)
shall be the same on each pole.
(d) Solid magnetic frames shall be used. Split frames shall not be used.
(e) The outside of the magnetic frame shall be a smooth figure of revolution.
Protuberances of magnetic material, such as feet or supports shall not be
used. Field pole bolts shall be recessed, and, in general, every effort
shall be made to ensure that the outside of the magnetic frame is a smooth
surface generated by revolving the arc of a curve about the axis of the machine.
(a) All parts shall be of nonmagnetic material unless otherwise specifically approved
by the bureau or agency concerned. Nonmagnetic material is defined as material
which has a maximum permeability of less than 2 after fabrication.
(b) The use of ferromagnetic material will be considered for the following parts only:
(1) Parts in the electrical magnetic circuits.
(2) Parts for which substitution of nonmagnetic materials would seriously
impair either the strength or satisfactory operation of the motor. The
use of magnetic materials, however, shall be approved by the bureau
or agency concerned.
(c) The use of nonmagnetic material shall not relieve the manufacturer of meeting
high-impact shock requirements.
3 . 6 . 2 Service C.-
188.8.131.52 General. - Protection against corrosion shall conform to Specicification MIL-E-917. Tem-
perature limits shall conform to table V.
184.108.40.206 Maqnet wire. - The magnet wire shall be of such size as to permit rewinding with one of the
types listed in table IV without affecting motor performance