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).
Forces, friction, and spring requirements of a longer armature motor.
| Identifier | WestWitteringFiles\T\November1928\ Scan090 | |
| Date | 17th December 1928 | |
| EFC1/T17.12.28. -2- Contd. Regarding the force of the spring with [handwritten: in] different positions, in this longer armature motor with the reduced armature taper, a longitudinal armature pull exerted by the motor in its fully disengaged position appears to be ample for overcoming all the ordinary friction of the bearings, brushes, etc. and a considerable spring pressure also. We have, however, shown that there may be failure to of the armature to start on account of having to separate two surfaces (e.g. representing the stop of the armature), whose plane is normal to the axis, when these surfaces have an oil or grease film between them. It is probable that we have the relation of longitudinal pull to armature rotation as you suggest (e.g. powerful end pull, gentle torque) and that rotation would not occur initially, so that whether rotation would assist the separation of the surfaces perhaps does not enter into the question. For the above reason, together with the fact that the springs do not come out exactly to requirements, the force of the spring in the two conditions of fully out and just entering engagement has been a little critical, though we have now arrived by experiment at a spring in which the quantities are [handwritten: seem] suitable. [handwritten: so far] Another point is the question of brush friction which, since there are eight brushes, causes a considerable solid frictional resistance to motion, and this has slightly increased the difficulties of suitable spring selection; this we have proved by actual removal of half of the brushes | ||