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).
Magneto spark experiment using an eccentric disc and synchronous motor setup.
| Identifier | ExFiles\Box 63\4\ scan0002 | |
| Date | 26th May 1918 guessed | |
| Contd. (2) Peripheral speed of H.T. point 92 ft/sec. FIG. B The stationary disc was arranged a little eccentric- ally, so that the length of gap varied from about 2mm. to about 6 1/2mm. and back again to 2 mm. during one revolution of the disc. In both cases (A) and (B) an insulated third point was provided as shown in sketches. (See note on third point). (attached) The motor to whose spindle the discs were fitted was a Bosch Z.R. 6 magneto with contact breaker and distributor removed, and brushes provided so that an alternating current at about 16 R.M.S. volts could be supplied to its primary winding. A supply was taken from the lighting mains at 200 volts and reduced to 16 volts by a small transformer. On running the magneto up to synchronous speed by means of string from the pulley of a D.C. motor, synchronising by the aid of an ammeter, and then removing the string by judiciously slacking it off, it was possible to get the magneto running as a synchronous motor of definite speed, viz. 2475 R.P.M. corresponding to a supply frequency of 41.25 cycles per second, and with amply sufficient stability for continuous running. Up to the present, the magneto sparks experimented upon are the following:- | ||