Alt-BEAM Archive
Message #05657
To: beam@sgiblab.sgi.com
From: Bruce Robinson Bruce_Robinson@bc.sympatico.ca
Date: Wed, 11 Aug 1999 22:58:32 -0700
Subject: [alt-beam] Re: Phototropic Bicore
Zulu35 wrote:
>
> i just made a head with a phototropic bicore found on ian's site.
> however, i do not have a gearmotor and to test it out, i connected the
> motor outputs to 2 LEDs, with the -ve side connected to ground. then i
> realised that the circuit does not lock onto the light source. :-( is the
> circuit supposed to do that?
> or is it supposed to lock on to the light source?
If I understand you correctly, you've built the circuit, but aren't
actually using anything to physically move the head.
Most of these circuits work by mounting a pair of photodevices on a
moving head and causing the head to turn whenever they receive differing
amounts of light. The head will turn until the light reaching both
photodevices is balanced, at which point it stops.
If you don't have something to move the head, you can't make it point
toward the light. Lacking a suitable motor, you can act like one
yourself, turning the head in the direction of whichever LED is lit.
(Or, depending on your circuit, turning it toward whichever LED is
unlit).
If this still doesn't work -- if you find yourself turning in circles,
then your circuit isn't properly balanced. Balancing is often more than
just adjusting a trimpot. You need to have two photodevices that are
reasonably well matched, and you need a good mechanical housing for
them.
My first head effort would turn endlessly in one direction unless it was
tracking a VERY bright light. The problem was mechanical -- the crude
photocell mounting was letting more room light get to one "eye" than the
other. A number of beamers have constructed "blinkers" using such things
a heat shrink tubing and the like. I solved my problem by machining a
symetrical head out of a block of ABS plastic.
I hope this gives you a few ideas. If not, give us a little more detail
about what your physical arrangement is and I'm sure someone will come
through.
Regards,
Bruce
5658 Wednesday, August 11, 1999 2:07 PM [alt-beam] "Linear Wheels" (was: LEM videos now on-line) beam@sgiblab.sgi.com John A. deVries II
>At 11:31 AM 08/11/1999 , Sean Rigter wrote:
>
>Zoz
>
Just a little side note to all of you out there. Although Wilf has made
mention of this before, I will say it again..... Sean is Wilf's son, Sean
has graciously allowed his father the use of his web access at home. So
when you see something posted by Sean, you are actually reading something
from Wilf when he is at home. And if you receive something from Wilf, then
he has sent the E-mail from his place of work.
Hope this helps to clear things up.
Les Davis
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