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).
Design review document with feedback and suggestions for a servo mechanism.
| Identifier | Morton\M20.1\ img011 | |
| Date | 11th April 1924 | |
| ORIGINAL SECRET. TO E.S. & ST.{Capt. P. R. Strong} FROM R.{Sir Henry Royce} Copy to - C.L. R.D. HS.{Lord Ernest Hives - Chair} DA.{Bernard Day - Chassis Design} HL. E.A.C.2 & 3. SERVO. Lec. 1861. X9960 Very disappointed with this design. It is extreme-ly involved; wanted someone to clean up. Too great a variety of parts and costly parts. For instance big central spring and floating plate could be replaced by providing main plate with 3pins thus - [Diagram Annotations] reduce to ¼" radial. As far out as possi-ble: close sliding fit. .01 clear here in dia. will ensure pins driving equally. These are the only parts where extra rigidity is required: other parts ap-pear too strong. Since these come so close togeth-er use 3 small cheap pins to carry short common spiral springs. These are better without bosses on forging because more room for springs. Friction faces have too much radial depth - reduce to ¼". Do not reverse bolts because waste of dia. Use thin nuts or clearance can be less as ferodo is shewn fully thick, and centre plate could be .2" or .15" and ferodo 3/16". clearance of faces .02" instead of .06". Last para. Ratchet nut has steps too high - suggest .020 as in Here is where pedal is losing stroke through servo clearance being too great - (see HS.{Lord Ernest Hives - Chair} report.) I am strongly in favour of flat plate servo because stress should be self contained and friction faces with such type must control end play. The 4 hardened ball thrust washers should be alike if possible, end of lever just sliding fit over both provid-ing support. Thrust thread may want to be 45° and might be better scintillaed or case hardened to ensure release, having coarse thread, and ample clearance. Nut might be bronze. There must be no doubt about a free release, but this scheme with double ball thrust is different to the agreed scheme and may have no risk of stick-ing with even 30° thread. The agreed scheme was said by HS.{Lord Ernest Hives - Chair} to be slow because of flat plate clutch, but that could not be the reason. I believe the servo was very slow speed with fairly large angle of action. This one is 7 to 1 instead of 28 to 1. (1) | ||