Levenkay wrote:Uh, it's been a loooong time since the DC Machines classes in college, but I seem to recall that playing with the amount of current running in a motor's field coils had a pretty big influence on the rpm-vs-applied-voltage characteristics. You could use a rheostat to modulate a motor's field strength, and still keep the heating losses in the rheostat fairly negligable, I think. Just don't let the field go to zero!
Yes - the control mechanism would use a small rheostat to control the DC exciter to adjust the power / torque characteristics of a DC motor. Much like an motor amplifier - google 'dc motor exciter' for more details and exciters were more often used for generator sets. Generators and alternators still need exciters but they are 'self exciter' driven - anyone remember having a generator needing a polarity reversal is an example of self excitation in the wrong direction.