Servo Question

3-Phase motors (380V) can be used as stepper. Provided it's derated to 40% or
so. At least that's the theory. Dunno if that was used in this case.
Guess IGBT could be handy for the controller ;)

On Wed, 19 Jul 2006 03:31:10 GMT, Idontthinkso@nospam.com (Mike_in_SD)


They have done this a few times. They don't go into detail on the
technical side, but on at least one occasion, it looked like a
windshield wiper motor to drive the steering wheel.

The principle of a monster servo is essentially exactly the same as
for normal servos: A motor to drive the load, a potentiometer to sense
the position, and a little electronics to drive the motor to where the
driver wants it.

In theory, you can build a monster servo like this:

- Take a normal RC servo and throw out the motor.
- Connect a powerful transistor driver where the motor was.
- Power the driver off the car battery.
- Let the transistor driver drive the big motor.
- Extend the wires for the servo pot and connect it mechanically to
the object you want to move.
- Done.

--
RoRo

I have built some small (well, maybe 10 times bigger than a standard
servo but smaller than the biggest ones you can get) servo systems this
way using a DC brushmotor and a potentiometer.  For feedback/drive I
used an AVR (with internal ADCs) and LMD18200 mosfet drivers.

You probably don't want to use the electronics from a servo; they are
built to be tiny and cheap and if you are building a large and
expensive servo they will be the limiting factor.  Since they take RC
signals you can only update the position at 50 hz.  They only do
proportional, not integral or derivative feedback, and the gain is
fixed.  It may be difficult to get a pwm/direction out of them if the
controller and driver are integrated.

chris

Robert Roland wrote:

Try this artical form lynxmotion.

http://www.lynxmotion.com/images/html/ht01.htm

The artical also has a contact email address for further questions.

Good Luck...

On Wed, 19 Jul 2006 03:31:10 GMT, Idontthinkso@nospam.com


DIY heavy duty:

http://www.cpg1.freeserve.co.uk/servos/servos.htm

These guys show this on their web site: http://www.roboteq.com/rcauto.html

I don't have any connection to them and have not used their stuff. I
think that Padu has though

Good Luck
Bob

this looked interesting but .. the guy worried me a little talking about
not actually testing the H bridge circuit or something like that.
But I did bookmark it.



oh yea .. this would work nicely, but .. at about 150 bucks per motor
it would hurt using it on a 5 axis arm.


thanks for the info guys
mike