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).
Calculations and specifications for a Bensport starter motor.
| Identifier | ExFiles\Box 62\1\ scan0139 | |
| Date | 18th May 1933 | |
| x6134 18.5.33. BENSPORT STARTER MOTOR. Engine torque when turning cold (0°C) estimated at 500 lbs. ins. Engine speed at this torque estimated to be 75 R.P.M. approx. Gear Ratio 9.60: 1.0 ∴ Motor Speed = 720 R.P.M. Assuming an overall mechanical efficiency of 80% the required motor torque will be 65.0 lbs inches. The motor power is therefore - .01184 x 65 x 720 = 554 watts. Assuming an electrical efficiency of .40 under the above conditions, the applied power would be 1385 watts or 156 amperes at 8.80 volts. Assume a useful polar flux density reckoned at the pole face of 6500 lines per sq.in. Armature diameter = 3.00 inches. Armature circumference corresponding to a 70% Polar embrace = 1.65" or 4.18 cm. Armature length = 2.875" or 7.31 cm. Flux per pole = 4.18 x 7.31 x 6500 = 199 x 10³ lines. Number of armature conductors required therefore :- | ||