The BEAM Bestiary is a BEAM
Moving toward a goal in
are essentially just pairs of solar
engines mounted together with motors; they seek out
bright sources of light through the differential action of
the two solar
engine motor pairs.
If you build a photopopper, and it doesn't want to work,
Wilf Rigter has a very good debug guide here.
Meanwhile, here are some debug tips from Dave
Hrynkiw of Solarbotics:
Date:Wed, 10 Feb 1999 01:19:29 -0700
Lesson 101 on how to check your Photopopper:
Preamble: Before doing ANY of the following, sit down
with your soldering iron and re-touch all the solder
connections. We find that 90% of the returns to
Solarbotics are fixed in under 30 seconds with nothing
more than a soldering iron and some solder to fix bad
solder joints. DO IT. Don't think "He can't mean _MY_
solder connections". Yup, I do. I have seen poor solder
joints on every returned item from somebody who INSISTED
that their soldering is perfect. Another thing - do not
be quick to blame your problems on a faulty component. I
have seen exactly 3 bad transistors _ever_. And NEVER a
bad 1381. With that said, let's begin.
Step 1 - Preparation: Didja mount tactile (touch) sensors
on it? Remove them. It cuts down on the complexity of the
Step 2 - 1381 testing: If it is running in circles (as it
most likely is), that indicates one side is obviously
dead, or seriously mistuned. Crank your trimpot all one
way - do you hear a slight buzzing? No? Crank it the
other way. Still no buzzing? That means there's a problem
with the circuitry to the 1381. Inspect your power and
ground connections to the 1381.
If you hear buzzing, that means the 1381 is trying to
trigger, but the solarengine isn't activating. No buzzing
= no 1381 action.
Step 2a - 1381 testing, part deux: Run a jumper from the
Vcc (positive) of your main cap or solarcell to the
middle leg of the suspect 1381. This will effectively
bypass all sensory inputs, and FORCE that 1381 to be the
one that will trigger, everytime. Does it work now? Check
the IR photodiode - may be in backwards. Did you forget
to install the cap for the 1381? Is the 1381 itself in
What, it still doesn't work? Even after checking that
there's a positive voltage on the middle pin of the 1381,
and ground to the right-side pin (viewed pins down,
text/flat side facing you)? Hmm. Must be the
Step 3 - Solarengine testing: Run a wire from positive
and _tap_ the middle leg pad of the 3904. Do this a few
times while watching the motor. Does it make the motor
spin? That's a good sign. Now notice carefully - does it
spin a bit longer after you remove the wire? Good, that
means the Solarengine portion of the circuit is working
properly. If it only works while you are holding the wire
to the middle (base) leg of the 3904, that means the
circuit isn't latching, or staying on. Your 3906 should
If you have not found your problem by now, start
reinspecting your handiwork for obvious flaws like a blob
of solder bridging solder pads, or improperly installed
components. Did you use glue to install the electronics?
Yes, I have seen this. It doesn't work. So don't do
Meanwhile, popper circuits are discussed over in the
For more information...
Ian Bernstein has pix of his really incredibly
small photopopper here.
For folks that want to build a photopopper,
there's no shortage of tutorials online. Chiu-Yuan
Fang's photopopper tutorial is here.
Ian Bernstein has a tutorial here
(he labels it a Solarroller,
but trust me, it's really a popper). Ian also has a
page on the BeamAnt (fairly advanced photopopper)
"Andy's light-seeking robots" has a pictorial
tutorial on a FRED-based
and Ray Diaz has a new one here.
There's also a (German language) photopopper page over on BeamPlanet
with nice pictures and video.