Alt-BEAM Archive

Message #03085



To: LiquidFord@aol.com
From: Wouter Brok w.j.m.brok@stud.tue.nl
Date: Sat, 08 May 1999 17:01:44 +0200
Subject: [alt-beam] Re: First Top'Bot


Hello,

While I was still busy with microprocessor controlled robots I've been
experimenting with what you suggested, but a whole pile of problems came up:
- the first and the biggest: reflection; in a room or any other environment
with obstacles there are quite a lot of sound-reflections, so basicly the
signal you get from one source is quite complex. Of course you can think up
something to get this problem out of the way. I tried do do it like this:
as a sound-source use something that generates bursts with silences
inbetween of a second or so (the typical time for sound to die out in a
normal room is 0.5 seconds. longer is irritating when you are talking in it
with someone) So then you can detect the direction of the first signal you
receive; all the reflections will come in later (easily to calculate with a
speed of sound of about 340 m/s in a normal environment). With that problem
out of the way:
- the second, as well difficult to solve: hoe can you make the microphones
direction-sensetive. the commercial microphones which are direction
sensitive are placed in a reasonably long tube, which isn't something you
want on your small robot. You can use more microphones pointing to
different directions and compare the signals from them (actually two woulk
be a good start), but the differences in signals are quite small, and with
me felt within the tollerance of the microphones (of course you can correct
for this ...).

Those were two physics-problems; my bet is that the electronics will also
pose a problem; I didn't come that far yet; when I saw the
oscilloscope-waveforms of the signals of the microphones I decided that it
would be easier to make a person-following robot with three PID-sensors -
the ones that are used to switch the light on on the lawn if a heatsource
is moving - but then I got to know about BEAM.

Maybe if you choose another, smarter way of detecting sound-direction it
will work out more easy ... I don't know ... it is an interesting concept,
definetely.

>I was wondering if anybody is working on an AudioTroph ? I have 3 left over
>microphones and was wondering if it was possible to get a BEAM bot to follow
>a certain sound or sound level? If any research or any plans are already out
>for this please let me know. By the way I created my first semi robot today.
>Its basicly a motor witha switch and battery but its a start right ?

yep, it definetely is ... if you get the hang of it you will be making nice
bots quite soon.

Regards

Wouter Brok




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