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).
Design calculations for a Peregrine starter motor with a 29 slot armature.
| Identifier | ExFiles\Box 62\1\ scan0102 | |
| Date | 12th December 1932 | |
| X 6134 12.12.32. PEREGRINE STARTER MOTOR. 4" Carcase. 29 Slot Armature. Engine Speed 90 R.P.M. at 0°C. Engine Torque 400 lb.ins. at 0°C. Gear Ratio 13 : 1 Motor Speed 1040 Overall mechanical efficiency - assumed to be 76.5% Motor conductor torque = 40.3 lb. ins. Motor power = .01184 x 40.3 x 1170 = 560 watts. Assume an electrical efficiency of .35. This gives an applied power of 1600 watts which on the usual characteristic of supply would mean an approx. current of 200 amperes at 8.00 volts. Assume a polar face flux density of 6500 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 6500 = 127,000 lines or 127 x 10³ Number of conductors required therefore = (40.3 x 2 x 10⁸) / (1.41 x 4 x 127 x 10³ x 200) = 57 nearly. Suggest an armature having 29 slots, 1 coil per slot 1 turn per coil. Motor Speed 1170 R.P.M. Back E.M.F. = (127 x 10³ x 58 x 1170 x 4) / (60 x 10⁸ x 2) = 2.87 volts. | ||