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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).
Calculation sheet for the torque required on 40/50 servo gears, including leverage diagrams.

Identifier  ExFiles\Box 16\3\  Scan017
Date  14th December 1927
  
X7370

Hs{Lord Ernest Hives - Chair}/Rml/LG14.12.27.

TORQUE ON 40/50 SERVO GEARS.

Maximum torque required from brakes is to lock
the rear wheels on dry concrete. Take limousine car 8-EX :
Rear wheel weight 32 cwts. = .8 .. Pull at rear tyres
25.6 cwts. Pull at 17" drum 48 cwts. Normal pressure
required on shoes, brake lining friction being .3 = 144 cwts.
.. Servo must produce this pull through existing leverage.

[Diagram text]
.5"
4.5"
2.15
3.35
2.5"
2.5
2.5 / 1.7
2.05"
--> P
3.8
5.575
3.8

Pull required at P. assuming EAC.7. leverage :-

144 X .5/4.5 X 3.35/5.50 X 1.7/2.5 = 6.6 cwts.

This is equivalent to a pull at the end of the servo 2.05"
lever of :-

6.6 X 7.6/5.575 = 8.7 cwts. at 2.05" lever.

Or torque from servo plates and servo driving shaft of 160
lbs.ft. say 170 lbs.ft. to allow for modifications to drums
or leverage.

Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}
  
  


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