Newsgroups: comp.robotics
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From: mwd@cray.com (Mark Dalton)
Subject: Re: Solar power transmission
Message-ID: <1994Dec21.174111.29917@walter.cray.com>
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References: <D14L00.2r9@acsu.buffalo.edu>
Date: 21 Dec 94 17:41:11 CST

Robert E. Okane (okane@acsu.buffalo.edu) wrote:
:   Greetings,
:I'll looking for ideas on how to implement some type of detection system for
:a population of solar powered robots. The robots we have are fuzzy logic
:controlled (no cpu) and avoid each other by detecting the shadow os the others.
:This is also how we detect the walls of the installation. However, we are now
:looking to create an "aggressive" population which would chase another robot.

	For if a robot was getting light 'All Electronics Corp.' has these
little 2mm photo???? (basically little solarcells in a class tube with two
wires), the more light they recieve the more current is produced.  I think
these may help (I have the specs. at home).  They are pretty cheap $.50 a
piece.

:The robots we have now are completely solar powered. This is necessary because
:we have 30 of them in the installation and to have to change that many
:batteries would be ridiculous and impracticle. Also we would like to have 50 or
:mare at one time running.

: I think some kind of identification /signal would be needed to distinguish the
: populations in some way. I though about color but this would be a bit tacky.
: (This is an "Art" installation)

: I have been told about some MAX chips that convert fluctuating low voltage
: (i understood from ~2.1V min) to a "constant" 5 volt signal. Does anyone have
: any experience with these chips? Do you think these could be a good place to 
: start? Could I get enough power from these chips to be able to drive a LED?
: How about the surface mount device LEDs? (Lasers ?)

: I looking for brain storming material so all offers are welcome.
: Thanks
: Bob O'Kane

Also Mark Tildens work is pretty interesting!  He has little park he calls
'Robot Juarasiac Park', it is a table in his office full of solar robots.
They are VERY cool and have no cpu's just transistors.

Here is the basic circuit design found posted:
Newsgroups: sci.electronics
Subject: Re: Solar cells and capacitors
Message-ID: <1991Dec3.150139.24012@watmath.waterloo.edu>
Date: 3 Dec 91 15:01:39 GMT
References: <1991Dec2.122934.27134@doug.cae.wisc.edu>
Organization: University of Waterloo

Try this:
 
 
          |-------------------O-------------O-----------------|
          |                   |             |                 |
          |               |-------|         |                 |
          |               <  mot. >-        |               + |
          |               |-------|         |                ---
          p      2.2k-10k     |           + |              -------
           n|--O---/\/\/------O           -----  >2200uF     ---    >2v solar
          P    |              |           -----  cap       -------      cell.
          |    |              N           - |                ---
          |----|------------|p              |              -------
               |              n             |               - |
              /-/             |             |                 |
               ^ Zener        |             |                 |
               | mc4742       |             |                 |
               |--------------O-------------O-----------------|
 
 
Legend:
               |                      |
collector-     P                      N                      |
base-      -|n     PNP trans.     -|p      NPN trans.    ----O----  wire join.
emitter-       p                      n
               |                      |
 
Essentially it's a modified SCR design with supercritical feedback.  The
zener starts clamping at vcc-.7v and will eventually trigger the PNP,
triggering the NPN, and will lock so long as the motor is moving.  The
beauty of this design is it's incredible high impedance until tripped.
For transistors, I've used 3904s and 3906s, but for higher power designs,
the NPN must be replaced with something like cascaded 2n2222s, or high
gain power transistors, like TIP 31s.  The zener should be rated to trip
at 2 volts below your solar-cell voltage rating to get maximum power.
 
This circuit is called the BEAM solarengine.  I developed it for the
Robot Olympics, used to build a solaroller device which covers a 1
meter distance in pure sunlight using only a cell 2-1/2" by 1/2".  I
promote it in my BEAM robotics package because of it's simplicity
and cheapness of parts.  What's your application?

-------------------< End of Mark Tildens Post >------------------------

I hope this helps.

Mark
-----
Mark Dalton       CH3-S-CH2 H H                    H      O       H
Cray Research,Inc.      |   | |                    |       \      |
Los Alamos,NM 87544     CH2-C-COO    //\ ---C--CH2-C-COO    C-CH2-C-COO
mwd@cray.com                | |     |  ||   ||     |       //     |
                            H NH2    \\/ \ / CH    NH3    O       NH3
                                          NH
URL = http://lenti.med.umn.edu/~mwd/mwd.html

