From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Calculation sheet for the Peregrine starter motor with a 4' carcase.
| Identifier | ExFiles\Box 62\1\ scan0085 | |
| Date | 12th November 1932 | |
| XG134 12.11.32. PEREGRINE STARTER MOTOR 4" Carcase. Engine Speed 60 R.P.M. at 0°C. Engine torque 375 lbs.ins. at 0°C. Gear ratio 13 : 1 Motor Speed 780. Overall mechanical efficiency, - assumed to be 76.5% Motor conductor torque = 37.7 lbs.ins. Motor power = .01184 X 37.7 X 780 = 348 watts. Assume an electrical efficiency of .22 under these extreme load conditions. This gives an applied power of 1580 watts which on the usual characteristic of supply would mean an approx. current of 195 amperes at 8.10 volts. Assume a polar face flux density of 7000 lines per sq. cm. Armature diameter 2.450" Armature circumference for 70% polar embrace = 1.35 ins. or 3.42 cm. Armature active length = 2.25 ins or 5.72 cm. Useful flux per pole therefore = 5.72 X 3.42 X 7000 = 137,000 lines or 137 X 10³ Number of conductors required therefore. 37.7 X 2 X 10⁸ / 1.41 X 4 X 137 X 10³ X 195 = 50 suggest an armature having 16 slots, 1 coil per slot 1½ turns per coil, or 25 slots 1 coil per slot 1 turn per coil. Motor Speed 780 R.P.M. Back E.M.F. = 137 X 10³ X 50 X 780 X 4 / 60 X 10⁸ X 2 = 1.78 volts. | ||