Subject:
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RE: r/c servos and firmware
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 20 Aug 1999 22:40:44 GMT
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Viewed:
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1440 times
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> It sounds to me like servos can't rotate continuously in the same direction. In
> other words, they're good for steering but not for turning the wheels that make
> the car go. Is that right?
There are multiturn servos for winches in RC sailboats, but they are REALLY
expensive.
> Anyway, having heard that (plus the paragraphs I deleted about calibration and
> software) I would have to say that servos don't sound all that useful. At least
> not as useful as I was thinking they would be...
Well don't give up too fast. They ARE useful for steering, or lifting, or grabbing
because we can set the limits of motion. This makes things like grippers really
easy to do without detecting motor stall current or using limit switches...
> How about using stepper motors instead? These are motors that have internal
> gear reduction and extra internal fixed magnets, and take pulses (either
> positive or negative). If the pulse width is right, each pulse makes it move a
> certain (fixed) number of degrees (the size of the step is the angular spacing
> of the armature arms divided by the gearbox reduction ratio). Are there any
> 9-volt stepper motors that work with pulses of 10 msec, or a multiple of 10
> msec?
Not quite. A typical stepper motor has 3 or four windings which must be energized
in the right sequence to go in the desired direction. They also have the nasty habit
of losing count, under load...it's not as easy as "putting in pulses" and having the
motor do what you want without some sophisticted motor driver circuitry...
Cheers,
Ralph Hempel - P.Eng
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Check out pbFORTH for LEGO Mindstorms at:
<http://www.hempeldesigngroup.com/lego/pbFORTH>
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Reply to: rhempel at bmts dot com
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Message has 1 Reply:
 | | Re: r/c servos and firmware
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| (...) That's not the type of stepper motor I'm talking about. I've seen the type you're describing, and they have the advantage that you can drive them with really slow pulses if you want. They're essentially just 3-phase AC motors. The kind of (...) (25 years ago, 23-Aug-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: r/c servos and firmware
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| (...) Okay! Finally I got it! (-: It sounds to me like servos can't rotate continuously in the same direction. In other words, they're good for steering but not for turning the wheels that make the car go. Is that right? Anyway, having heard that (...) (25 years ago, 20-Aug-99, to lugnet.robotics)
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