Servo Question

     I love the PC GUI's available for the standard R/C servo applications. Like the Lynxmotion stuff ..
Where you can say .. position the servo here .. at this speed etc.
anyways ... It would be cool to use these interfaces with some really big stuff ..
Im not talking about the normal 150oz servo's, im talking real big
which brings up a question .. I watched mythbusters the other nite and he was controlling (steering ) a car with a normal R/C xmitter ..
what was he using on the car end ????
thanks mike
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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 ;)
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On Wed, 19 Jul 2006 03:31:10 GMT, snipped-for-privacy@nospam.com (Mike_in_SD) wrote:

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


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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:

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On Wed, 19 Jul 2006 03:31:10 GMT, snipped-for-privacy@nospam.com (Mike_in_SD) wrote:

DIY heavy duty:
http://www.cpg1.freeserve.co.uk/servos/servos.htm
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Mike_in_SD wrote:

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
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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
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