Starter motor as servo?

[wile_e]

Would it be possible to use a car starter motor as a servo?
Has anyone tryed it?

[Al_The_Man]

It is dangerous to operate a series connected motor such as a starter motor without a high load, if no load is present, the field current decreases and the motor can start to run away, often to the point of destruction!.
BTW you may wonder why the series wound motors (Universal) found in power tools etc do not fly apart is because small motors have a built in degree of regulating friction load which large motors do not.
Al

[wile_e]

Is not this a possible solution?
http://homepages.which.net/~paul.hil.../Starters.html

[wile_e]

Here is some more info...
http://homepages.which.net/~paul.hil...otorsBody.html

[Al_The_Man]

Those sites are interesting, but it seems to me they still intend to use them as traction motors, as that what series motors are used for, and are just allowing some control of speed. I would question as to wether they would be usefull used in normal servo use, as the field is still in series with the armature and as such I would think the control will not be precise. DC servo motors of all sizes, typically have a shunt field, wether Wound or Permanant magnet, whereby the field strength is known and is constant.
Maybe someone here has done this and may be able to shed some more light.
Al

[wile_e]

Could you not have the fieldcoils powered by a separate adjustable powersupply and thereby making the motorcaracteristics somewhat adjustable?

[Al_The_Man]

Yes, you could probally turn it in to a shunt connected (parallel) field motor and this would allow precise control of the field current. see http://www.engin.umich.edu/labs/csdl...ors/dc/ser-dc/
Al

[gus]

it is my understanding that servo motors are wound specially to, among other things, reduce decel current and operate at low speeds

[Al_The_Man]

Originally Posted by gus it is my understanding that servo motors are wound specially to, among other things, reduce decel current and operate at low speeds

Yes, years ago DC servo motors were used that had wound fields, before the advent of super magnets etc, but they did not have quite the low speed resolution that modern servo's have and they were extremely large compared with todays dc servo's with permanent 'super' magnets and skewed wound rotors etc.
Al

[wile_e]

Originally Posted by Al_The_Man Yes, years ago DC servo motors were used that had wound fields, before the advent of super magnets etc, but they did not have quite the low speed resolution that modern servo's have and they were extremely large compared with todays dc servo's with permanent 'super' magnets and skewed wound rotors etc. Al

Most of us will propably use it in "geared down mode" , say 1:50 - 1:100 , giving that the motor can run at higher revs. Would not that be a a consideration?

[lerman]

Remember that while a starter motor does see some very rough service, its usage is very intermitent.

The starter motor on my car is used about a minute per day. That's about 6 hours per year. You might find that you have to replace the brushes once a week.

I do recall seeing an article once that suggested using a car alternator as a motor. I believe the conclusion was that it didn't have much power, but I don't remember why.

Ken