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).
Performance calculations and proposed modifications for the 40/50 starter motor.
| Identifier | WestWitteringFiles\K\June1923\ Scan3 | |
| Date | 4th June 1923 | |
| TO EFC. FROM R.{Sir Henry Royce} c. to GJ. c. to BY X9620 40/50 STARTER MOTOR. ORIGINAL R4/M4.6.23. 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.lbs.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 an 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 lbs. 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 lbs. ins. be running with about 20% less flux than stated in your calculations. The advantage of the normal load having less than the maximum flux is that the torque will increase with the square of the current and the motor speed will decrease with the load, and therefore the demand for current in the case of overload will be less, and owing to the increased efficiency of this motor and it's increased torque and efficiency the drop in speed and the demand on the battery would (1) [Handwritten note in left margin]: EFC We will see if Mr Hives has referred to the point [Top right corner]: 2 | ||