Subject:
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Re: odometry (was 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 12:02:47 GMT
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Original-From:
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Laurentino Martins <lmartins@AVOIDSPAMmarktest.pt>
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Viewed:
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1348 times
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At 09:20 28-07-1999 Wednesday , Mario Ferrari wrote:
[snip]
> Yes, 95 ticks are always 95 ticks, but the point is if your robot really *is*
> in the position where it's expected to be on the floor. The main problem with
> odometry, as you know well, is that errors accumulate very fast. The
> unavoidable slippage of the tracks makes the things worse. From what I read so
> far about detecting a robot position, tracks are the worst choice. See, for
> example, the great "Where am I? Sensors and methods for Mobile Robot
> Positioning" by J.Borenstein (freely available on the net but can't remember
> where).
I've downloaded, printed and read it all some time ago :-)
> > My conclusion is that identical tracks (left/right) have identical slippage
> > _if_ the floor is identical below both the tracks and the bot has symmetrical
> > shape and weight.
>
> True. But when dealing with odometry I still prefer to avoid slippage by
> design instead of relying on *identical* slippage of the tracks.
>
> > I think the same happens with differential drive (?).
>
> In a good differential drive there is no significative slippage of the main
> wheels.
I've used 2 wheels instead of tracks once, and the results where terrible compared with tracks.
The problem was that the wheels that come with the CyberMaster set are very deep like the F1 car wheels (they are the only ones I have). When doing tight turns they show a god mount of slippage.
But the worst problem was that the third wheel was a free wheel.
I would never guessed that, but it turned out that the "free wheel" is bad because it makes the whole vehicle very inaccurate.
The simple motion stopping the vehicle and reversing the engines, make the "free" wheel turn 180 degrees and because it's axis is off-center, it forced the vehicle slight changes of direction.
It was not good at anything, not even for straight paths because slight oscillations in the free wheel direction had a great impact on the direction of the vehicle.
Here's my free wheel:
vehicle
_________
#
OOOO #
OO OO #
O #####
OO OO
OOOO
I need to find a better design...
Laurentino Martins
[ mailto:lau@mail.telepac.pt ]
[ http://www.terravista.pt/Enseada/2808/ ]
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 3 Replies:
 | | Re: odometry (was Re: Homing with the IR Tower)
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| (...) I see your point. Yes, F1 kind wheels are far from ideal to avoid slippage and get accurate results. The larger but thinner spoked wheels that come with the Minstorm RIS are quite better. The free wheel(s) also must be light and thin and (...) (25 years ago, 28-Jul-99, to lugnet.robotics)
| | | Re: odometry (was Re: Homing with the IR Tower)
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| (...) Great source. Just found a source where Johann Borenstein discusses the original 1966 paper and gives links for the full electronic version or a CDROM or a book version. Here is the source: (URL) for the pointer! Ralph M. Deal deal@kzoo.edu -- (...) (25 years ago, 28-Jul-99, to lugnet.robotics)
| | | Re: odometry (was Re: Homing with the IR Tower)
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| I haven't done any 'bot yet but I have been thinking about this problem. and here's the result: it looks like the good free wheel should do its 'wheeling' equally well in each direction. therefore it should be a ball. the design should look like (...) (25 years ago, 31-Jul-99, to lugnet.robotics)
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Message is in Reply To:
| | Re: Homing with the IR Tower
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| (...) I've built a PC program for the CyberMaster that pools the integrated tachometers continuously and shows the trajectory of the bot in the PC screen. It uses _tracks_, and I've found out that besides one of the tracks runs a bit better than the (...) (25 years ago, 27-Jul-99, to lugnet.robotics)
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