Subject:
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Re: Homing with the IR Tower
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 28 Jul 1999 01:58:29 GMT
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Original-From:
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Michael Aaron Finch <goblintrain@uswest.netNOMORESPAM>
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Viewed:
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1268 times
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Mario,
i am still intrigued by your creative response to posts. Good luck. & may
the force be w/u.
Michael Aaron
Mario Ferrari wrote:
> In lugnet.robotics, Chris Phillips writes:
> > In lugnet.robotics, Hao-yang Wang writes:
> > > A while ago I was intrigued by the soda can retrieval challenge.
> >
> > I'm glad to hear that I'm not the only person who's still trying to solve
> > Joel's challenge. It sounds like you've made some great progress!
>
> I'm intrigued too by Joel's challenge. This was the reason for I started my
> experiments with odometry months ago. The problem is always the same: much
> more projects in mind than time to carry them out :-)
>
> <snip!>
>
> > > The robot is a standard two-track design. It has two motors, each drives a
> > > track with a 1:3 gear reduction. It uses two rotation sensors as tachometers
> > > to maintain its heading. The rotation sensors are not connected to the • motors,
> > > but to two unpowered wheels. This way the rotation sensors still detect the
> > > actual movement of the robot even when the tracks are slipping. The wheels • are
> > > suspended in a way that maintains their contacts to the ground even on an
> > > uneven terrain.
> >
> > I had considered switching to a tracked design also, and thought of using this
> > approach of having non-driven encoder wheels in contact with the ground. I
> > had trouble getting the wheels to maintain solid contact so I put it on hold.
> > I was trying to spring-load my wheels to hold them on the ground, but it
> > sounds like you're having better luck just using old-fashioned gravity?
> >
> > Do you find that you are able to get fairly accurate odometry using this
> > approach? I think the entire Mindstorms community could benefit from somebody
> > figuring out how to track linear motion and turns reliably.
> >
> > My latest design uses a six-wheel drive setup with three wheels on each side
> > which are direct-geared to spin as one. I have found this to be much easier
> > to work with than the tractor treads so far, and it grips so well, I half
> > expect it to climb up a wall while I'm not looking! For now, my encoders are
> > driven directly off the wheels, but I plan to eventually incorporate some kind
> > of free-floating odometry wheels if I can get them to track properly.
>
> I believe that tracks (or wheels coupled to behave like tracks) are a poor
> choice to get good results from odometry. I mean, as this mechanical
> arrangement relies on slippage to turn, it's unprecise for its own nature.
> IMO a differential drive is much more suitable to get the best from odometry.
>
> > > 1) Can detection. I have an interesting idea of detecting soda cans using
> > > Dennis Clark's IRPD: The robot wanders around. When it detects something in
> > > the IRPD, it does a bit of wall-following. (See my earlier post
> > > <http://www.lugnet.com/robotics/?n=4527>.) From the readings of its two
> > > tachometers, the robot can deduce the shape of the "wall". If the "wall" is a
> > > cylinder with a diameter in a certain range, then it may be a can.
> >
> > This is similar to my latest approach. I'm using an IR-radar "ping" to locate
> > the can. When I'm close to (and directly facing) an object, I turn a few
> > degrees left and right, comparing the ping values to either side of the peak
> > reading. I'm still trying to tune the heuristic, but the idea is that if the
> > ping is much lower on _both_ sides, it's probably a can. If _either_ reading
> > is comparable in magnitude to the center peak, it's probably a wall. (Since
> > my odometry isn't anywhere near perfect yet, I'm trying to minimize any
> > movement during this process.)
>
> I have another idea about using the Dennis Clark's IRPD to detect cans: we can
> turn it 90 degrees so the left and right detectors are on the same vertical
> line and become "bottom" and "top" detectors. Placing the sensor at the proper
> height on the bot, we should be able to tell if an obstacle is a wall (bottom
> detection only) or a can (bottom and top detection at the same time).
> Obviously I assume that the walls are higher than the cans :-)
>
> Hope this may help your project. I'll start mine sooner or later :-)
>
> Mario
>
> http://www.geocities.com/~marioferrari
> --
> Did you check the web site first?: http://www.crynwr.com/lego-robotics
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message is in Reply To:
 | | Re: Homing with the IR Tower
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| (...) I'm intrigued too by Joel's challenge. This was the reason for I started my experiments with odometry months ago. The problem is always the same: much more projects in mind than time to carry them out :-) <snip!> (...) motors, (...) are (...) (...) (25 years ago, 27-Jul-99, to lugnet.robotics)
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