In article ,
Tom Veatch wrote:

On Mon, 19 Jan 2009 21:54:24 -0800 (PST), whit3rd
wrote:

Electrically reversing the motor is probably psosible
(usually these have brush-style motors, you could
reverse the brush polarities);

I assume this is an AC motor. Don't the brush polarities reverse 60
times per second already? Or possibly I'm not understanding what
you're saying?

They do indeed reverse 120 times per second (60 full cycles per second),
but so does the field coil, so the relative magnetic polarity of the one
with respect to the other stays the same. In other words, the repulsion
or attraction of the two doesn't change. By swapping the brush
connections, the magnetic polarity of the rotor with respect to the
stator is reversed and the motor forced to turn in the other direction.

Motors of this design are often termed "universal motors" because they
will operate properly on AC or DC current, and furthermore are not
particular about AC power frequency. My RAS with such a motor is
specified as being for either 25Hz or 60Hz AC; I assume 50Hz would also
be OK. DC is presumably not listed because of the power switch being
insufficient to properly cut off high DC currents, not because the motor
would fail to work properly.

--
Andrew Erickson

"He is no fool who gives what he cannot keep to gain that which he cannot
lose." -- Jim Elliot