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 motor resistance, armature, and slot area.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 199 | |
| Date | 22th June 1927 guessed | |
| -3- Contd. Total motor ohms = .026 = R Let field resistance = RF and armature " = RA Then R = 1.3 RA + RF to allow for brush and commutator resistance. Suppose RF = .6 RA then R = 1.9 RA or RA = .0137 ohm } (similar to present RF = .0082 ohm } standard 40/50 6" motor). These resistances are considered to be their values at 20°C in accordance with assuming engine cold for the value of its turning torque. Resistance of one armature turn at 20°C = (.0137 x 4) / 45 = .00122 ohm Length of armature turn = 11" approx. Resistance per 1000' = (12000 / 11) x .00122 = 1.33 ohms. But ohms of copper per 1000' at 20°C = .00815 ÷ cross sectional area in sq.ins. Whence a = .00815 / 1.33 = .00613 sq.inches. Allowing 40% space efficiency in slots, slot area = 2 x (.00613 / .40) = .031 sq.inches (say) Total area A of all slots = 45 x .031 sq.inches = 1.395 sq.inches. Contd. | ||