Re: [CAD_CAM_EDM_DRO] Unknown servo motors...

Harvey White wrote:

>OK, I have some Minertia servo motors, and the specifications seem
>rather hard to get...
>
>Is there a reasonable procedure to go about to determine the motor
>characteristics? If so, where would it be documented?
>
>

There are two numbers that can be obtained from the motor with relatively
simple measurements. They are related, so you only need to measure
one. If you have a mill or lathe with well-known spindle speeds, chuck
the motor to the spindle, and run it at around 1000 RPM. Measure the
DC voltage generated by the motor. Correct for the whatever spindle
speed you are getting, and you have the Kv constant. this is normally
expressed as Volts/1000 RPM. So, if you have 1200 RPM, take the
voltage/1.2 and you have Kv. Multiply Kv * 1.351 and you have
Kt, the torque constant, in Oz-In/Amp units. If Kt was 45 V/1000 RPM,
then Kt must be 45 * 1.351 ~= 70 Oz-In/Amp.

The hardest numbers to get are continuous torque and peak current.
If you exceed the continuous torque rating the motor will overheat
and eventually break down the winding insulation. If you exceed
the peak current, even for an instant, you can demagnetize the
magnets, altering the Kv and Kt constants, usually much for the worse!

The continuous torque ratings can usually be guessed at by comparing the
motor to others of similar size and construction. If the motors run cool
all the time, you probably don't have much to worry about.

The peak current is often in the range of 2 - 4 X the current equivalent
to the continuous rated torque.

Jon