DC motors worthy of being a servo?

[NC Cams]

Some monstrous DC motors can be found in treadmills. High commutator bar count and smooth running. Mucho RPM and HP.

The ones I got have a small shaft thingie sticking out the non drive end (blower fit on it) with could easily accept a hollow encoder. Don't appear to be direction sensitive although they only run one direction.

Wiper motors are continuous duty BUT tend to be unidirectionally biased for preferred torque output in direction of prime rotation. Yes, they'll run backwards BUT that is only to park the wipers. Most are bushed too but some of the Japanes ones are ball bearing equipped.

Keep in mind that some servos have two pairs of brushes and two sets of magnets - similar to a car starter. This is another way to get cog free operation and more torque at a low current density.

Now, if you go to a high speed motor and 4:1 or 8:1 gear reduction, torque will be massive and the cogging won't be as noticeable due to the gearing.

Yes, almost any DC motor will make a servo. A plow horse can also be entered into the Preakness. But, a plow horse won't suffice as a racing thoroughbread just as a car or wiper motor fall a bit short of a true servo motor for some applications.

It all depends on your needs, goals and satiability.