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 special dynamo brushes and analysis of output variation issues after production tests.
| Identifier | WestWitteringFiles\V\2January1931-April1931\ Scan033 | |
| Date | 3rd February 1931 | |
| -2- In addition to the above, in the Phantom case experiments are in hand with special Morganite brushes (Link 5, H.M.5, H.M.6, EC.6630 and EC.60.) mostly having a lower coefficient of friction. We have also in experimental progress, brushes with an increased degree (30°) of top bevel together with experimental brush springs to suit and this modification appears, so far to be a satisfactory improvement. We have recently included in the Phantom (medium output dynamo) production test specification, suggestions for dealing with this trouble pending the results of the above experiments. (2a) Initial variation of output after production test. Some fall of output occurs, apparently in some machines only, after leaving production test, which fall has been established to be due to a blackening of the control brush along the trailing edge this virtually moving the centre of contact area in such a direction as to decrease the angle of control brush span. In those machines in which the phenomenon does occur it appears to occur irrespective of whether the original brush bedding is good or indifferent. The phenomenon gives the control brush the appearance of having two beddings, the trailing portion being dull to black while the leading portion is polished. There are not, however, two beddings in the sense of the brush tilting but only in the sense of the narrowing down of the active bedding surface (polished) leaving the rest of the surface dull to black and more or less inactive. To the extent to which this occurs it does not appear to have any more serious effect than in the alteration in the output, therefore some allowance may be and has been made for it in the original setting of the control brush. Production have been advised, through the test specification, that after bedding the brushes and cleaning the commutator of a machine which has a tendency for this to occur, they should not try and remove it but allow it to develop normally on the final 3 1/4 hour run. | ||