Subject:
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Re: Motor speed
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 22 Nov 2002 17:16:39 GMT
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Viewed:
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956 times
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In lugnet.robotics, "Brass Tilde" <brasstilde@insightbb.com> writes:
> > > the two motors appear to operate at slightly different speeds.
> > > Is this something that is usual?
> >
> > Yes.
>
> I figgered that was the case. <sigh>
>
> > If you are using multiple motors to drive a small robot one
> > way to compensate is with rotation sensors, or use a single
> > motor and a differential to get the robot to drive straight.
> > Or maybe use multiple motors and a differentially-driven
> > single rotation sensor to detect the difference in the two
> > motor speeds.
>
> At the moment, it doesn't interfere with anything, as I am just starting to
> build things and am just now building the roverbot and going through the
> various "challenges". I'll keep those in mind though, for when I understand
> everything you're talking about. <g/> I am a programmer by trade, so the
> physical relationships between the parts are more arcane and challenging for
> me than the programming aspects.
>
> Maybe I'll get the kids to explain it to me...
>
> Is the power adjustment fine enough to compensate for this sort of thing?
> Setting one motor to 7 and the other to 8 or something?
>
> Thanks,
> Brad
Trying to adjust the power settings probably won't work - not only do the
motors vary slightly, but also their performance varies with the battery life.
But with Mindstorms there are usually several different ways of overcoming
any particular problem! If you have more technic lego than just the
RIS(specifically another differential) you can implement a very nifty dual
differential which will ensure both wheels go at the same speed. It
basically lets one motor control forward/back movement, and the other
control turning. It is explained quite nicely here:
http://www.cs.dartmouth.edu/~robotlab/robotlab/courses/cs54-2001s/dualdiff.html
Like you I find the mechanical side far more mystifying than the
programming, but I also find it fascinating.
Another possible solution is a differential and a rotation sensor. (If you
only have the RIS, then you can simulate a rotation sensor with a touch or a
light sensor). If the wheels are connected with a differential, then if one
wheel is moving faster than the other, the differential will rotate. Connect
the rotation sensor to the differential to work out when you aren't going
straight.
Hope this helps
James
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Message has 1 Reply:
 | | Re: Motor speed
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| (...) may "drift" slowly. But you can block it with the clutch gear, then it needs real some motor force to turn. Jürgen (22 years ago, 22-Nov-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Motor speed
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| (...) I figgered that was the case. <sigh> (...) At the moment, it doesn't interfere with anything, as I am just starting to build things and am just now building the roverbot and going through the various "challenges". I'll keep those in mind (...) (22 years ago, 22-Nov-02, to lugnet.robotics)
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