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 of calculations for armature dimensions and copper wire properties.
| Identifier | ExFiles\Box 64\2\ scan0075 | |
| Date | 1st June 1927 guessed | |
| -4- Contd. But ohms of copper per 1000' at 20°C = .00815 ÷ cross sectional area in sq.inches. Whence a = .00815 / 1.22 sq. inches. = .00668 sq. inches. i.e. 13 S.W.G. dia. .092" By comparison with 20 HP. slot, width of slot = .148" depth " = .500" or .020" less if banding wire is omitted. Armature circumference = 3.100" Pitch = (π x 3.100) / 29 = .336" Width of tooth at top = .188" Bottom of tooth is at 3.100 - 2 x .450 dia. i.e. at 2.200" dia. Pitch at this diameter = (π x 2.200) / 29 = .238" Width of tooth at root = .090" If banding wire is omitted (as suggested), then bottom of tooth is at 3.100 - 2 x .430 dia. i.e. at 2.240" dia. and pitch at this dia. = .243" whence width of tooth at root = .095" | ||