Re: [CAD_CAM_EDM_DRO] DC Motors

Jason Cox wrote:

>Hello,
>
>
>After searching through the archives I found some discussion on using DC treadmill motors as servo's. Some said that this was not a good Idea due to brush design etc.
>
>What im wondering is will any standard dc brush motor with encoder mounted operate as a servo even if only for a limited life. The positioning of the motor, acceleration etc would only be dependent on the controller and encoder? Or is there more that I need to be thinking about.
>
>

Any motor that has a built-in encoder is more likely to be suitable as a
servo motor.
There are several factors that go into a servo motor for positioning
service. One of
the biggest is torque ripple and velocity ripple, variations in torque
and/or velocity
when turning at low speeds. This is a consequence of the winding
design, ans somewhat
of the general construction of the motor's rotor and slots. Motors
designed for operation
in one direction only may have tilted brushes, and brushes which are not
in line
with the stator fields to account for armature inductance. These motors
may perform
badly, or wear out the brushes and commutators when run in the reverse
direction.

Permanent magnet motors have to be protected from even very short
overcurrents, as
this can demagnetize the field magnets, rendering the motor essentially
useless.
The peak torque and continuous holding torque of any particular motor
has to be
taken into account when designing the drive setup. The proper choice of
belt
reduction ratios will make the whole system perform better.

Finally, if the motor has a wound field, instead of permanent magnet,
the field must be
set up for shunt operation, as a series-wound field motor is not reversible.

Jon