Ned Simmons wrote:
On Thu, 11 Jun 2009 21:55:15 -0500, "Karl Townsend"
wrote:

"Bob Engelhardt" wrote in message
...
Is a servo motor simply a DC motor with an encoder or tach? Or is there
something about the motor itself that makes it a "servo motor"?

Thanks,
Bob
A DC servo is just a DC motor with a feedback device. You can make a DC
motor into a servo by adding an encoder. Richard Kinch has a web site
showing his effort.

Now a good DC servo is designed for high torque at low speed without burning
out. A DC motor you pull off the shelf won't be optimized for this.

Motors that are marketed as servos also usually have lower inertia
than typical motors and magnet materials that are more resistant to
demagnetization under high peak currents. Both important features for
high acceleration, but often overkill in modest applications.

In addition to that, servomotors, at least the
ones I've disassembled, appear to be built to
higher standards than plain motors. Better bearings,
closer rotor/armature-stator fit, more rigid frames,
better brush holders and lead terminations.