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 for the 40/50 starter motor and proposing new overload test conditions and design modifications.
| Identifier | ExFiles\Box 64\1\ scan0137 | |
| Date | 4th June 1923 | |
| +7620 To EFC. from R.{Sir Henry Royce} c. CJ. c. By.{R.W. Bailey - Chief Engineer} R4/M4.6.23. X.S620. 40/50 STARTER MOTOR. I am in receipt of your calculations with reference to the starter motor - 40/50. This motor and the 30 to 1 reduction gear makes an easy, light, and efficient problem. We can therefore look upon it as turning an engine which is still larger or still colder than the 1400 lb.ins. demanded. You will see that as we have made the problem too easy for you we propose increasing the imaginary load so as to arrange the motor best for overload. One of the results of this scheme is that we are carrying either a larger motor or a little more gear instead of a larger battery. I therefore propose that you examine the motor under the conditions of 2200 lb.ins. torque required for the engine in a very cold condition when the engine speed may have dropped to 33 RPM., corresponding to approximately 1000 RPM. on the motor. Under these conditions we anticipate the current will nearly have reached 180 amps. My own recommendation is that we increase the number of sections from 37 to 41. We use the same flux as at present in the overload, namely, with the 180 amps. It would then with the 1400 lb.ins. be running with about 20% less flux than stated in your calculations. The advantage of the normal load having less | ||