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).
The frictional effects and forces acting on a brush within its holder and on the commutator.
| Identifier | ExFiles\Box 50\5\ Scan227 | |
| Date | 1st October 1928 | |
| Contd. -4- EFCI/T1.10.28. In the majority of cases, the brush in position in its holder and on the commutator can be tilted over so as to cause an entirely different bedding thereon. Though the bedding of the brush may be correct at one moment and running nicely and may remain correct so long as it is not touched, there is sufficient frictional effect between the surface of the spring and the top of the brush to allow the mere lifting of the spring and lowering again on to the brush to cause the brush to meet the commutator at a slightly different angle. This has been demonstrated. If one could say that the frictional effect was negligible, then the force exerted by the spring on the brush would be exactly normal to the surface of the brush at the bottom of the spring slot, upon which the spring bears, but it will be agreed that since the commutator exerts, on account of friction, a tangential force at the bottom of the brush and that this has a moment about the lower edge of the brush holder against which the brush is held, the tendency, apart from the force exerted by the spring, will be to throw the top of the brush against the opposite side of the holder. Thus it depends upon the magnitude of this moment and the magnitude of the frictional force exerted at the contact of the spring with the brush (i.e. on the way in which the spring is lowered on to the brush) to which side of the Contd. | ||