There is nothing that differentiates a cheap little 3-commutator segment toy motor from a sero motor except quality. The former is completely unsuitable for servo use because of torque ripple while a good quality utility motor may qualify.
Torque ripple is how much does torque change as the motor rotates over a revolution. Servo drives are tuned to a motor's torque response. Ideally they expect the same torque no matter what clock position the motor is at.
With cheap motors this varies a lot. With excellent motors it varies very little. Cheap motors can never be tuned, good ones tune easily.
What makes a good motor? A lot of commutator segments and a skewed (spirally twisted) low-cog armature. Brushes that are not preferentially set for a particular direction.
The range of motors from the cheapest to the most expensive is a spectrum. Pass a certain threshold and a utility motor can be a good servo motor.
Mariss |