Society of Robots - Robot Forum
Mechanics and Construction => Mechanics and Construction => Topic started by: B.Glen on April 27, 2008, 04:32:06 PM
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Has anyone ever used a moving coil galvanometer (volt meter) instead of a servo? Would it work as a silent alternative? Any ideas about control issues?
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a servo is a motor. it doesnt measure anything. it just moves where you tell it to
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Galvanometers are sometimes used to control mirrors and move them rapidly and quietly in laser displays etc...
I was wondering if anyone had used them to build robots. An analogue volt meter is a example of a very small galvanometer.
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Aside from possibly moving small sensors around, a galvanometer is not capable of producing the force(torque) required to be very useful in the world of robotics.
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im sure they have more powerful ones than the ones in voltmeters
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As the topic starter said, stronger variants of the galvanometers are used in laser displays. So yes there are much stronger ones.
I think they'll cost you though...
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this is a diagram of the galvanometer
(http://br.geocities.com/majtec/images/Eletronica/Galvanometer_diagram.png)
So i'm assuming putting stronger magnets in there would give it more torque.
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Ok, let me rephrase: pound for pound, dollar for dollar useage a galvanometer is not going to have the torque that a servo will, and will use more energy for "hold" positions. It would be good for very precise sensor movements. You can make anything more powerful, but is it worth it?
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Ok, let me rephrase: pound for pound, dollar for dollar useage a galvanometer is not going to have the torque that a servo will, and will use more energy for "hold" positions. It would be good for very precise sensor movements. You can make anything more powerful, but is it worth it?
well said
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Any ideas about control issues?
Sorry, didn't mean to skip over this question. If you were going to use one for something in a robot, control could be handled through a DAC feeding an OPAMP to the Galvanometer. Your MCU could then directly control the amount of rotation for the Galvanometer by varying the signal sent to the DAC.
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Thanks for the advice. I’ve found some plans for building large galvanometers, so it’s something to consider. Besides accuracy, the benefits might include very low noise levels and no servo burn out from extended use.
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Keep in mind that your winding core for the galvanometer will likely eventually pick up a residual magnetic field. Even layered transformer iron (which is what I think is usually used) will become magnetized. A Ni-Alloy (Ni-49 or Kovar, etc) core will help avoid this, or you can build a degauser into the galvanometer.
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Besides accuracy, the benefits might include very low noise levels and no servo burn out from extended use.
Not true, those problems will still exist - it works on the same physics as a DC motor :P
I think the main advantage is that you can miniaturize this and use it for micro-robots. Servos are much harder to miniaturize . . .