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 and design of an electrical starter motor compared to a Lucas model.
| Identifier | ExFiles\Box 34\3\ Scan153 | |
| Date | 5th April 1918 | |
| To EFC. from R.{Sir Henry Royce} c. to CJ X.2642. 5th April. 1918. R1/CS.4.18. X.2642. X.3161. RE ELECTRICAL STARTER MOTOR. With reference to the electrical starter motor, it seems quite evident that the Rolls-Royce motor when compared with the Lucas, is built for a much slower speed, and you will see that it gives a torque of, say, 100 lbs for about half current. It is for this reason that I suggested you should test it with a higher voltage, so as to make to give both a greater HP and also [handwritten: partly] to, test, it at this increased voltage with the field coils all in [handwritten: parallel] ~~series~~ (?) You will notice that if it were fitted with very fine winding or supplied with a very low voltage, that its speed would be still lower, and its efficiency also. At the time it was designed, we were anxious to keep the current down, and it would be found that by substituting what appears a more efficient motor, such as the Lucas "A", that the battery, cables, and switches, should all be made larger and heavier. If this were not done the consumption of current would be so great as to risk destroying them. The alternative would be to put in a high ratio of gear between the motor and the engine. This also was fully realised when the R.R. motor was designed, and was suggested by us to the Air Board, resulting, in the production of the still lighter Lucas. I may say in conclusion, that your report of the increase efficiencies of the other motors somewhat surprised me at first, but I think it can be entirely accounted for as above. R.{Sir Henry Royce} | ||