Subject:
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Re: Rack-and-pinion steering line tracker
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 9 Jan 2000 18:27:02 GMT
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Original-From:
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The WordMeister <wordsmth@ici.net^AntiSpam^>
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Reply-To:
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The WordMeister <DWILCOX@antispamWORDSMITHDIGITAL.COM>
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Viewed:
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568 times
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[May the rest of the group forgive me for pointing to my design again--but I
was obsessed with it for a month ...]
http://www.wordsmithdigital.com/mindstorms/rack-and.htm .
:)
--The WordMeister
Doug Wilcox
WordSmith Digital Document Services
403 VFW Drive
Rockland, MA 02370
781-871-6162
fax 781-871-6264
http://www.wordsmithdigital.com
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-----Original Message-----
From: Mark Rendle <rendle2000@hotmail.com>
To: lego-robotics@crynwr.com <lego-robotics@crynwr.com>
Date: Sunday, January 09, 2000 1:15 PM
Subject: Re: Rack-and-pinion steering line tracker
> I'm working on my first original robot, having built the 3 in the
> Constructopedia and modified them a bit. I'm currently on my 4th R&P • design:
> the first two just didn't work, and the 3rd had a turning circle larger • than
> my living room. It incorporates a light sensor by running a second set of
> gears off the motor drive, and attaching a 2x12 plank to a large cog (40
> tooth?). The light sensor is mounted on this, currently using an L-bend to
> point it at the floor, but it will also point forwards when I have a go at
> proximity detection.
> Again, it's stunningly clunky. If anyone knows of or has a LEdit file of an
> elegant R&P system I'd love to see it!
>
> --
> Mark R
>
> www.markrendle.co.uk
> Tilman Sporkert <lego-robotics@crynwr.com> wrote in message
> news:NCBBKPAJLICLDDABDHAMAEEADGAA.tilman@activesw.com...
> > I too spent quite some time trying to build a steering mechanism from • standard
> > Mindstorms parts. After many rebuilds I still wasn't quite satisfied. The • final
> > version actually worked pretty well, but was much too bulky (not as bulky • as
> > Doug's version however :-) ), and the wheels were tilted inward too much • for my
> > taste. So I decided to see what I could do with some more specialized • Lego
> > parts. I could have just bought the service pack with the various Lego • steering
> > mechanism parts from S@H. But no, I decided to use it as an excuse to buy • all
> > sorts of Technic sets. Along the way I learned that Lego can't make up • their
> > mind about how to build a steering mechanism either. There are so many
> > variations!
> >
> > About the return to center problem: My solution is to incorporate the • light
> > sensor into the steering mechanism. Mount it at the end of a short arm • pointing
> > forward, ahead of your wheels. This has two advantages:
> > - You will get a much smoother steering vehicle, with gradual steering
> > movements.
> > - You don't have to worry about centering the steering mechanism.
> >
> > With the traditional approach, you will be sensing that you are off the • track.
> > But you don't really know how far to turn the wheels to stay on the • track.
> So
> > you make a best guess, turn too far, until you are back on center. Now • you
> have
> > to figure out how to go straight again.
> >
> > With my approach, you keep the light sensor on the track all the time, • and
> the
> > vehicle sort of follows it. As soon as the sensor moves off center, you • start
> > steering to keep the sensor on the track. The steering system is now part • of a
> > direct feedback loop, and will always point in the right direction.
> >
> > This of course doesn't make the steering system any easier. You now have • to turn
> > three things - the two wheels, and the arm that holds the sensor.
> >
> > Tilman
> >
> >
> > > I spent a _lot_ of time trying to get a non-sensored R&P steering • system
> to
> > > work, using pulleys, rubber bands (both as drives and springs), and
> > > you-name-it! I finally gave up, but did manage to build one with only • _one_
> > > sensor that was very effective.
> > >
> > > See http://www.wordsmithdigital.com/mindstorms/ for a scan and my • described
> > > history of running my head into the wall. Should get you started in the
> > > right direction--or avoid getting you started in the wrong direction.
> > >
> > > Ironically, I've started playing with roboticizing the 8479 as well!
> > >
> > > --Doug Wilcox
> >
> >
>
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