Continuous servo vs. DC with encoder?

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StrangeQuirk
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Continuous servo vs. DC with encoder?

Postby StrangeQuirk » Tue Nov 13, 2012 12:35 pm

Could someone explain the difference between a continuous rotation servo (like 3202) and a DC motor with an encoder? I was under the impression before that a servo is nothing more than a DC motor with some gearing, an encoder, and an H-bridge, so I was surprised that DC motors with encoders are significantly more expensive than servos here.

I need a winch that would give me precise control over both position and applied force, and I'm trying to minimize costs. I'm also pretty new to all things hardware (which is one of the reasons I'd like to use phidgets), so any tips would be useful.

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Patrick
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Re: Continuous servo vs. DC with encoder?

Postby Patrick » Tue Nov 13, 2012 1:27 pm

Continuous rotation servos don't have any position feedback, they just turn when powered. They are also much more cheaply built / weaker then a DC motor with metal gears, etc.

StrangeQuirk
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Re: Continuous servo vs. DC with encoder?

Postby StrangeQuirk » Tue Nov 13, 2012 4:29 pm

Oh. But then why are they called servos? I thought the definition of a servomechanism was that it had a negative feedback loop.

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burley
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Re: Continuous servo vs. DC with encoder?

Postby burley » Tue Nov 13, 2012 4:58 pm

You are correct, technically continuous rotation servos are not actual servomotors. The name implies a form factor and control style more than anything.

You can read more about it here:

http://www.pololu.com/blog/24/continuou ... urn-servos
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