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).
Statement regarding the adoption of a new armature design with 28 slots and 56 coils to make the dynamo quieter.
| Identifier | ExFiles\Box 165\6\ img056 | |
| Date | 18th January 1927 | |
| X5661 18.1.27. STATEMENT CONCERNING THE ADOPTION OF ARMATURE HAVING 28 SLOTS AND 56 COILS; ONE OF THE COILS BEING A LAP COIL. Our present armature has 29 slots and 57 segments! In order to make the dynamo quieter, it is desirable to make the number of slots a multiple of four. The alternatives are :- 7 x 4 = 28 slots. 8 x 4 = 32 slots. An armature having 32 slots, and two coils per slot, would require 64 commutator segments. This is too many. For 28 slots, there would be 56 segments, and 56 coils or virtual slots. The winding is to be a wave, and preferably retrogressive. This applied to 28 slots results in 55 coils and a dummy. The dummy, however, can be afterwards inserted as a lap coil with another segment, making 56 coils and commutator segments. A wave winding then, is required to suit 55 virtual, i.e. 4n -1 slots, and 110 virtual conductors. A winding based on an equal slot pitch cannot be obtained with this number 4n -1 of slots, but would require 4n +1 slots. With an equal conductor pitch, each pitch would be 27. This will not do, however, as, owing to the use of | ||