This book is brilliant. It isn't stylish, it's not lavishly illustrated, it isn't even a riveting read. It is, however, plain old fashioned lucid. Hughes is or was an academic, and if he lectured as well as he writes, his students understand electric motors.
He also speaks with authority. The diagrams are small, mostly simple black-and-white drawings, but they fit in with the text,
It isn't for everyone though. You'll want at least 'A' level physics to understand it and (despite his protestations) it is fairly mathematical.
By far the best book I've read in this subject area for a while