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).
Comparison of the electrical and mechanical properties between a Lucas machine and a Rolls-Royce machine.
| Identifier | WestWitteringFiles\V\2January1931-April1931\ Scan075 | |
| Date | 30th March 1931 | |
| EFCL/AD30.3.31. contd. -2- Both Lucas and R.R. machines have four poles. The ohmic resistance at 18°C. of the field winding of the Lucas machine is 4.75 and of our own machine 2.6 ohms. The Lucas machine has 23 slots as against 28 in the R.R. It has 45 coils or commutator bars as against 56 in our present standard 2C/25 machine. The size of the armature conductors in both machines is 19 S.W.G. The armature resistances of the two machines are almost the same so that the probability is that the Lucas machine has nearly the same number of conductors — the very possible number of conductors per slot compared with that of the R.R. machine is in the ratio of 5 to 4, but the number of conductors cannot be arrived at without destroying the armature. In the Lucas machine the air gap is trailed off on both the leading and trailing edges, being .0175 at the centre, increasing both ways to .0475 at the pole tips. The main brush material and size on the two machines is approximately the same but in regard to the control brush, this on the Lucas machine is very much narrower than our own and its brush holder is such as to provide a trailing angle of 16°, whereas our control brush in common with all the main brushes of both machines, is set normal to the commutator. In all machines of this type the main brushes are retarded from about 5 to 15° from the static neutral position on the commutator, Lucas is retarded 5° and our present standard machine 8°. In respect of the control brush angle, it is our custom to express this in its positional relation to the positive brush; the supplement of this angle is then the real control brush angle in electrical degrees. Our present standard angle is 123.5 corresponding to a control brush angle of 56.5° span; Lucas, as received, was 115° corresponding to control brush angle of 65° span. | ||