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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).
Experiments with different dynamo armature designs to achieve silent operation.

Identifier  ExFiles\Box 38\3\  Scan295
Date  10th October 1921
  
To EFC. from R.{Sir Henry Royce}
c. CJ PN.{Mr Northey} Hs.{Lord Ernest Hives - Chair}
c. Mr. Bentley.
c. Mr. Hulley.

COPY. Y33/62

RL/G10.10.21.

X.294. RE DYNAMOS. X.1640.

Regarding the silent dynamos, you will remember that some time ago we obtained some sort of proof that, at my suggestion, an even number of sections in the armature might do much towards making the dynamo silent, owing to the fact that with an even distribution of poles the armature would always be in magnetic balance.

Royce Limited of Manchester are making me a dynamo for the house and office lighting here. I am having three armatures made for this dynamo, one of which will be one coil per slot, the second one being two coils per slot, an even number of slots and a dummy. The third one will have an uneven number of slots, coils grouped in three, and naturally no dummy.

These three armatures will be run for the same purpose in the same carcase, and should shew definitely

(1) if there is any advantage in fine slotting,
(2) if there is any advantage in even numbers, as regards silence.
(3) and whether an equally good dynamo could be made with the most practical arrangement of coil which is three per slot for four poles.

As regards the number of teeth on the armature, and the number of sections in the commutator for the three grooving, we calculated that there are certain numbers distinctly advantageous, and supposing these numbers of

Contd.
  
  


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