Investigation report into the cause of 'singing' noise from a Rotax A.T.12 dynamo.
| Identifier | WestWitteringFiles\F\April1921\ Scan91 | |
| Date | 19th April 1921 | |
| R.R.C.(T 02) H 211 (10-3-21) C 3008 To R. {Sir Henry Royce} from EFC. {E. Fowler Clarke - Electrical Engineer} c. CJ. & PH. c. Ey. & Bn. {W.O. Bentley / Mr Barrington} c. De. ORIGINAL. EFC {E. Fowler Clarke - Electrical Engineer} 12/T19.4.21. X.294 - SINGING OF DYNAMOS (WITH PARTICULAR X.100B. REFERENCE TO ROTAX AT.12 DYNAMO) with reference to your note R4/C4.5.20, we have investigated your ideas in connection with the Rotax dynamo and the following is my assistant's report on the matter :- "The Rotax A.T.12 dynamo has 14 slots and 4 poles. At a certain instant there will be exactly three teeth (i.e. two and a half tooth-space pitches) under each of one pair of opposite poles. There will then be exactly three spaces and two teeth under the other pair of opposite poles, leaving one tooth-space pitch between adjacent poles. As the armature moves through half a tooth-space pitch, this condition will move through 90°, i.e. the first pair of poles will now cover two teeth, and the second pair three. There will thus be 28 reversals per revolution of the armature. Further, since the teeth spiral by a little more than half a tooth-space pitch, all the above effects will take place rather more than 90° later at one end of the armature than at the other; but the teeth under the poles will always be equal and opposite. The poles are not chamfered off at the edges." EFC. {E. Fowler Clarke - Electrical Engineer} | ||
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).