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 a lengthened armature type sequence starter motor with a 16:1 ratio.
| Identifier | WestWitteringFiles\T\November1928\ Scan056 | |
| Date | 27th November 1928 | |
| SV EFCL/T27.11.28. ---------------- SEQUENCE STARTER MOTOR. LENGTHENED ARMATURE TYPE FOR 16 : 1 RATIO. This motor is calculated below on the basis of an engine speed of 40 and a motor speed of 640 r.p.m. The motor conductor torque is taken as 90 lb-inches which, allowing a motor mechanical efficiency of 90% and a gearing ditto of 85% corresponds to an engine torque of 90 x 16 x .90 x .85 = 1100 lb-inches nearly. The power on the conductors in watts is .01184 x 90 x 640 = 682.5 A reasonable electrical efficiency to expect of this motor at the above speed and torque is .452 *which means (on our assumed characteristic of supply) a supplied power of 1510 watts or 180 amperes at 8.4 volts. This will allow a good margin for stalling torque within the maximum available power of 300 amperes at 6 volts. Contd. + The maximum efficiency will occur at a higher speed and lower torque and be higher than this. | ||