Subject:
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Re: Ultrasonic sensor interactions
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 21 May 2006 12:09:19 GMT
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Viewed:
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2453 times
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In lugnet.robotics, David Schilling wrote:
> In lugnet.robotics, steve <sjbaker1@airmail.net> wrote:
> > John Barnes wrote:
> >
> > > Pulses emitted by "the other sensor" can arrive at just the wrong moment,
> > > creating a false range reading. Clever numerical filtering can eliminate this
> > > kind of thing under certain circumstances - for example you may be following
> > > parallel to a wall and obtaining a series of readings which should be all within
> > > a likely range. If you suddenly receive a reading which is outside the expected
> > > range, you might discard it. In otherwords, if you maintain an average and only
> > > accept readings within a certain range of that average as bona fide, then you
> > > may be able to guard against this kind of interference to a certain extent.
> >
> > A better alternative would be to develop protocols in which the NXT
> > controllers use their communications to tell each other what they are
> > about to do. If you can sent a message that says "I'm about to do an
> > ultrasound 'ping' - so you'd better ignore any readings you are about
> > to get and refrain from doing a 'ping' of your own." then do a range
> > measurement and finally send another message "Thanks - I'm done with
> > the ultrasound system for a while."...then the systems can arrange to
> > avoid interfering with each other.
> >
> > After all, robots move slowly - you are unlikely to need high speed
> > readings.
> >
> > I guess it all assumes that you have software control of the ultrasound
> > sensor so that you can control when it sends a ping and make it shut
> > down between pings.
> >
> > For competitive NXT events, it might be worthwhile for this group to
> > come up with a standard protocol that contest organisers could
> > require everyone's entries to adhere to if they wish to use the
> > sonar system.
>
> This is a great idea except for one very important item: there is no such thing
> as a broadcast message (ie: a message sent to everyone) using Bluetooth. So for
> any such system to work, each robot has to know about every other robot, and
> send individual messages to them all. In a competition environment (especially
> something like FLL), that likely won't happen at all -- there are too many other
> NXTs that you have to set up communication with. Even in a more structured and
> less crowded environment, it isn't a trivial problem because of the limited
> number of BT channels.
>
> *Possibly* a better solution (I've not tried it, so who knows!) is to set up a
> scheduling system: synchronize the clocks on the NXTs in the area with a set of
> BT messages. Then each robot has its own pre-specified 1/5th of a second that it
> can use the ultrasonic sensor. Depending on how accurate the clocks on different
> NXTs are, once a minute or so you might need to resynchronize all the clocks.
>
> --
> David Schilling
How about a single computer that was Bluetooth accessable. The server could act
as a "lockable" resource that a NXT could acquire prior to doing the US
detection. Then the NXTs don't need to know about each other, just the main
server (and it should be able to communicate with many other devices and not
bound by the NXT's limitations). Perhaps Bluetooth communication hasn't got the
speed for this to work well though.
It sounds like the bigger problem is that currently no one knows how the shut
the US sensor completely off via software.
-Tim
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Message is in Reply To:
 | | Re: Ultrasonic sensor interactions
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| (...) This is a great idea except for one very important item: there is no such thing as a broadcast message (ie: a message sent to everyone) using Bluetooth. So for any such system to work, each robot has to know about every other robot, and send (...) (18 years ago, 21-May-06, to lugnet.robotics)
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