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).
Servo cam angles, coefficients of friction, and load loss for the Phantom and 20 HP models.
| Identifier | ExFiles\Box 16\3\ Scan032 | |
| Date | 21th December 1928 | |
| Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} from DA.{Bernard Day - Chassis Design} c. to Wcr. BY.{R.W. Bailey - Chief Engineer} +7370 DA{Bernard Day - Chassis Design}3/M21.12.28. SERVO. X.5370 X.7370 We thank you for your Hs{Lord Ernest Hives - Chair}/RmL/LG18.12.28. We have gone over our figures again, and we have also searched back through the files for the information on the Phantom servo and the 20 HP. servo. All this information, including the very latest practice, indicate that the Phantom cam is 55° and not 45°. Perhaps you could clear up this point. With a 55° cam and a multiplication on the Phantom servo of 2, we make the co-efficient to be approx. .32 so that we do not understand your .150 to .2 co-efficient. We should have thought in any case that Ferodo would have been more than this. We have investigated the pins, and assuming a co-efficient of friction between the pin and its bush of .2 we find that on the Phantom the loss of load is approx. 8.8%, and on SS.{S. Smith} 9.2%, treating each servo in exactly the same way. Since this is an increase of loss of .4 of 1%, it seems scarcely likely that it will be appreciated. The reason why (though the radius on SS.{S. Smith} is much smaller than Phantom) the loss of load is so slight is because the end load is so much greater in proportion. We might point out that when the 20 HP. servo was first tested (Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}2/LG27.5.25) a similar series of complaints was made, and it was found that on the arrival of the second servo they were not really justified, as the second one was much more powerful. With reference to the alteration to the ratio of direct braking, we are not at all sure about this, and think we shall have to get a decision from R.{Sir Henry Royce} Fortunately it is very easily varied. Rather than drop the cams to 30°, should any alteration be necessary, we should prefer to increase the length of the cam levers a certain amount. DA.{Bernard Day - Chassis Design} | ||