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).
Notes on the gear ratio for an A.T. Speedometer, model A.677.
| Identifier | ExFiles\Box 59\2\ Scan014 | |
| Date | 6th February 1930 | |
| X.4308 6.2.30. A.T. SPEEDOMETER No. A.677. N.800. Notes on gear ratio. Main spindle has two-start thread. Engages with 16 tooth wheel on shaft. Single worm on shaft. Engages with 11 tooth wheel on counter spindle. Total reduction to counter spindle 88 : 1 Inside counter :- Spindle carries eccentric on which floats a double pinion having 21 and 23 teeth. This pinion rolls round in engagement with internally toothed rings having 24 and 26 teeth respectively. Larger ring is mile drum, smaller is fixed. This gearing produces a creep of mile drum at - 1/91 times speed of counter spindle or spindle does 9.1 revs. per mile. Thus total main spindle revs. per mile = 88 x 9.1 = 800.8 | ||