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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).
Page 2 of a report detailing dynamo specifications, weight, and bench test results.

Identifier  WestWitteringFiles\H\November1921\  Scan1
Date  11th November 1921
  
Contd.
-2-
The proportions of armature and carcase are as follows :-
Carcase diameter 5.0"
" length 3.15"
" thickness .385"
Armature diameter 3.75"
" active length 3.1"

The weight of the machine complete with pulley but without suspension is 24.75 lbs. (This includes the additional weight of the special bearing plate which has been arranged by R.R. for this machine).

On the bench tests which we have carried out the dynamo has run consistently well, with the exception that there has been some slight evidence of magnetic hum and also rather undue amount of brush noise.

The makers' representative saw this machine running on our tests and they have now sent us brushes of a different quality, namely, H.M.6 for the purpose of reducing this noise. These will be tried out in due course.

Further particulars of the dynamo are as follows:-
Weight of armature complete without pulley but with bearing and end plate - 8.75 lbs.
Air gap. .0145"
Field circuit resistance -5.38 ohms at 18°C.
No. of armature slots - 25.
No. of comm. bars or coils - 25.
Armature resistance at 18°C - .385"
Commutator diameter - 1.875"
Useful length. - 1.125"
Brush contact area - .850" x .175" = .1487 sq."
Overhang of armature conductors at driving end - .8"
Length of commutator connections (exclusive of comm. spokes) - 1.150"
Ditto (inclusive of comm. spokes) - 1.375"
  
  


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