Difference between D.C. motor and D.C. generator

[IO390]

I know that a D.C. motor and generator both work on the same principle, and that if you turn the shaft any D.C. motor, it becomes a generator.

I am wondering if there are any notable differences in the physical design and construction of a motor and generator?

Thanks in advance.

[SeanB]

Generally the differences are brush angles, as they have to be different to get the best out of each application. Most older jet engines use a generator as a starter motor, having a simple controller that changes the excitation current and the windings to a control loop when the engine speed is high enough. They can charge the battery at the same current as they use to start, which can be truly impressive. from flat and barely capable to finish the start cycle to full charge in under 2 minutes. Can be very bad for a battery unit that has gone marginal in any way. They can rival lithium batteries in explosive venting, and are bad in that they have a negative temperature coefficient when charging. Rated start current draw on some is over 8kA.