someone said:

 >The normal "improvement" is a pulsed supply that provide full voltage
 >for a varying period - ie PWM. The theory is that high resistance
 >contacs such as tracks to wheel, engine brushes/comms (if still used)
 >switch contacts etc are broken down by the application of full voltage.

"the theory" is actually that torque in a DC motor is proportional to
the applied voltage regardless of RPM.

-- rob

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