[phil spanner]

To better understand servo's. Is a servo motor a dc motor with an encoder.
Could I put an encoder on a 12 v car windshield motor !!!.
Thank you Phil

[chihuahuacnc]

maybe not a windshield motor, but a window elevator i think it will work, because windshield motor is a dc compund motor, an a window elevator is a pemanent magnet field motor, wich means that has less torque but beter speed regulation.

[WayneHill]

Phil,

Almost. Servo motors are made to handle speed changes and reversing direction. DC motors are usually made to run in one direction.

For a hobby application, yes you can mount an encoder on a DC motor and it will work. Done it myself with good results.

[phil spanner]

maybe not a windshield motor, but a window elevator i think it will work, because windshield motor is a dc compund motor, an a window elevator is a pemanent magnet field motor, wich means that has less torque but beter speed regulation.

Thanks. Its answered my question but I thought windshield motors are permanent magnet motors. When you mentioned compound motors, does that mean you cannot make it into a servo whether its wound shunt or series.
Still learning after all these years. Phil ,Hope, British Columbia.

[Al_The_Man]

All DC motors are not created equal, even permanent magnet type, The general purpose type have less poles usually, and this results in cogging at low rpm's.
Even so they will work to some degree in simple servo applications, but DC servo's, apart from higher pole count, have features like skewed rotor laminations that the coils are wound on to produce much smoother operation down to zero rpm.
Automotive motors are made as cheap as possible so for the cost of good servo's on eBay etc, it is not worth considering.
Al.

[phil spanner]

All DC motors are not created equal, even permanent magnet type, The general purpose type have less poles usually, and this results in cogging at low rpm's.
Even so they will work to some degree in simple servo applications, but DC servo's, apart from higher pole count, have features like skewed rotor laminations that the coils are wound on to produce much smoother operation down to zero rpm.
Automotive motors are made as cheap as possible so for the cost of good servo's on eBay etc, it is not worth considering.
Al.

Thank you. Phil. Hope, bc.

[N4NV]

This is a picture of a good DC brushed servo motor:

http://www.cnczone.com/forums/attach...chmentid=15240

It has a skewed rotor and 4 brushes. One quick way to tell if a DC motor can be used as a servo is to run it from an AA battery. Even servos up to 100 VDC will turn nice an smooth from the 1.5V battery. If it turns with a jerky motion, keep looking. The motor in the picture will run smoothly at 0.26V and .2A at about 1 rpm even though it is over 1/2 HP and draws 8A at full load.

If you look further through the thread:
http://www.cnczone.com/forums/showthread.php?t=18178

you can see I added encoders so the motors can be used as servos with a Gecko 320 drive.

Vince

[ViperTX]

Ah....no....that's why they have different names.....encoders are not the requirement to call a DC motor a servo.....

[N4NV]

True, but an encoder is required to run from a Gecko 320.

Vince