Alt-BEAM Archive

Message #09975



To: beam@sgiblab.sgi.com
From: Ben Hitchcock beh01@wyrm.its.uow.edu.au
Date: Thu, 10 Feb 2000 11:14:43 +1100 (EST)
Subject: [alt-beam] Re: walker phototropism


Hi,

> I just got some help from Mark T. on phototropism, and he sent me some
> info I don't quite understand, so I thought perhaps you could take a whack at
> explaining what he means to me. Mark T. wrote:
> "Just take a few photodiodes with resistors in series and introduce them
> across the coupling resistors of your robot. Depending on the diodes, how
> they are pointing, and how your robot's mechanics are arranged, you can
> figure out how to give your critter eyes."
> I am trying to build a two motor bicore phototropic walker (eventually
> with reverser). Can please explain what Mr. T mean's (and think 'see spot
> run' language, I am really not an engineer). Any help would be appreciated.

You probably already know that changing the resistor values on your
bicore will change the timing of the cycle. That is, if one resistor is
larger than the other, then one neuron will turn on for longer than the
other one. If each neuron controls a motor, then the bot will take longer
steps in one direction than the other direction, resulting in it turning
around in circles. Much like walking with a limp, really.

Anyway, what Mark was saying is that you can turn a photodiode into a
variable resistor. Imagine that when the bot is pointing left of the
light, you make the left motor turn on for longer than the right motor,
and when pointing right, make the right motor turn on for longer. You
will have a robot that will turn towards the light, and set off on a trek
into the sunset.

To make the resistors be affected by light, grab a photodiode, attach a 1
Meg resistor to it, and attach the other end of the resistor to an input
of a neuron in the bicore. Ground the other end of the photodiode.

Now changing light levels will make the on-time of that motor vary,
depending on which way around the PD is, and how your bicore is set up.

Repeat for the other neuron in the bicore, point your PDs in different
directions, and voila! Your bot will be AFFECTED by the direction of the
strongest light source. It might run away from it, it might head towards
it, it might head at 90 degrees from it. Now comes the time for physical
experiments, which is what Mark was talking about.

hth,

ben



9976 Wed, 9 Feb 2000 15:34:05 -0800 (PST) [alt-beam] Re: RoachBot Photovore beam@sgiblab.sgi.com "Travis D." and which part # would that be? I just got mine from
DigiKey and they're a different setup--they're round
and plastic cases (they're the part # from Chiu's
site)

--- TurtleTek@aol.com wrote:
> In a message dated 2/9/00 4:35:13 PM Central
> Standard Time,
> lifebytes_98@yahoo.com writes:
>
> > What is the blue thing inbetween the photodiodes
> on
> > that bot? I've seen them on a lot of robots, and
> > always wondered, but never asked before. My guess
> is a
> > pot in a different packaging than most I've seen
>
> That's right. It's a pot. The ones we get from
> Digikey (and many other
> places) are blue.
>
> >Is that what it is? It's blue, and has a little
> > metal piece that has a groove in it like a flat
> headed
> > screw head. Is that the adjustment part of the
> > potentiometer?
>
> Right and right again.
>
> > Sorry for the dumb question, but the
> > curiosity finally got the best of me.
>
> No problem
>
> -Brien the TurtleTek
>
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9977 Wed, 09 Feb 2000 19:01:23 -0600 [alt-beam] Re: aggravating little pager motors.. beam@sgiblab.sgi.com Tod Dow
What I do is clamp the weight with vise grips and put the motor between the
jaws of the vise just to get a solid surface. Don't tighten the vise. Then I
pop out the motor with a jewelers screwdriver and a hammer. Just be careful
to avoid hitting the motor with the screwdriver.

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