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 specifications and performance requirements for a starter motor.
| Identifier | WestWitteringFiles\J\May1923\ Scan9 | |
| Date | 16th May 1923 | |
| R.R. 235A (100 T) (S.H. 159. 11-8-20) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 2800 ORIGINAL TO EFC. FROM R.{Sir Henry Royce} SECRET. R1/M16.5.23. c. to GJ E.{Mr Elliott - Chief Engineer} A.{Mr Adams} C. X.9620 STARTER MOTOR. This certainly should be the size having a 5" dia. carcase. In considering what possible improvements we might make to the proportions, we have come to the conclusion that the carcase could with advantage be increased in thickness as suggested by you, and send herewith drawing No. LeC.1719. shewing revised carcase and pole piece dimensions. The worst average conditions under which the motor will be called upon to operate are those of American winters. For these conditions we have assumed a temperature of 10° below F.{Mr Friese} zero, and considered that there will be only 8 volts available at the battery terminals when the motor takes 200 amps. which we anticipate will be needed to produce the torque required, and the windings should be suitable with these volts to turn the engine at 40.R.P.M. the motor then doing 1200.R.P.M. (about 30 to 1 gearing.) As soon as you can, let us have your proposals for number of armature teeth, and armature and field windings. It should be remembered that we require the amp. turns to be expended chiefly for air space and armature teeth, very few for the yoke, and only a small percentage for the magnet cores. After deducting 3 volts for the cables, switches, brushes, there will only be 5 volts for armature reaction volts and current resistance losses in the motor. With the 8 volts the efficiency of the motor should be 50% which will be about 30% taken from the 12 volt battery. R.{Sir Henry Royce} | ||