Motors

A router is a "universal motor" it will run (the same?) on AC or DC.
It is not reversible. Some hand drills have this type of motor also
and they are not reversible. Speed will vary with voltage and torque
seems pretty good except very low speeds. Frequency drives will not
work. To have it reversible I think you need another set of
windings. I don't know why, but they only run one way.

In the "old days" you could power most of your corded tools with a
simple generator made from a car alternator to easily produce 100 ish
DC volts. Most tools that are not reversible are universal motors.
Jig saw, router, sawzall, circular saw, most of these will all run on
DC. Look on the motor lable it will say AC/DC. Bench tools are
mostly AC synchronous motors. 1800 and 3600 rpm which is a function
of number of poles (I think) and line frequency. Some reversible and
some ain't.

A cordless drill is a DC brush motor, easily reversible, and most use
a simple linear Pot., direclty coupled to the trigger, to control
speed

Many tools are popping up with "electronic variable speed" which are
the PWM and SCR drives mentioned. I think they have flatter torque
curves than just cutting the voltage.

I am not a motor expert. I just plug them in to different supply and
voltage combinations to see what happens. A variable DC supply and a
variac are great for testing motors. An Ammeter also makes playing
with motors easier to "see" what is going on.

Joe V.