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).
Analysis of starter motor performance, comparing the torque and resistance of 41 and 45 slot armatures.
| Identifier | WestWitteringFiles\S\June1928-August1928\ Scan136 | |
| Date | 29th August 1928 guessed | |
| -4- Contd. The fact that the static torque is less in spite of the larger number of conductors appears to indicate an inferior magnetic circuit. The armature resistance is also greater - .014 ohm as against .008 ohm. The object of the 45 slot armature was to get the higher torque at a given current, but in changing from the 41 to 45 we appear to have over-stepped the optimum balance of iron and copper, and the result is not so good. In order to arrive at the generally best performance result, we consider it necessary to try experimentally with this taper armature a range of main field windings of varying numbers of turns, and presumably reverting to the 41 slot armature. The observations we consider of major importance upon a starter motor are :- (1) The maximum static torque (i.e. torque on the conductors) obtainable on the motor when the current is at such a value as to correspond, together with the necessary voltage to the characteristic of supply. This torque will be about 10% higher than the actual brake stalling torque of the motor on the characteristic. (2) The speed characteristic of the motor on a brake torque base. It is considered that in this connection a curve which shows a high stalling torque, but not necessarily rising greatly in speed as the torque is reduced, is much to be preferred to one of the opposite variety. EFC. | ||