"Wild_Bill" wrote in message
...
It's likely that the HF router speed control is a very simple diac/triac
circuit. These are very useful for lighting loads, lowering the
temperature of a soldering iron, or other small loads (the label rating
suggests 15A max, IIRC).

The trigger/switch circuit in VSR variable speed drills (for example) is a
better circuit for maintaining motor torque at lower speeds. This is a
characteristic of PWM pulse width modulated circuits.
Many PWM circuits don't require a speed sensor device at the motor, so
they can operate well with only 2 wires for motor power.


You can run series wound universals using DC servo amps too, as long as the
amp has a setting to run in IR mode--I've done this several times and
generally you'll get fairly stablw speed control under widely varying loads.

Specifically, I used the AMC model 25A20--one thing though, it's quite
possible to overspeed the motor with this arrangement in which case the
results could be downright spectacular.