■ FIGURE 3.
■ FIGURE 4. Inkjet arm
on RoboSpinArt Machine.
to an EFX-TEK Prop- 2 board (a very
convenient BASIC Stamp II based
controller). I wrote some code that
would dump a single line of text to the
serial print interface and then start the
servo motor spinning. I placed a blank
white ping pong ball on the servo and
then held the inkjet cartridge at the
“equator” of the ball.
Even with the inkjet cartridge
hand-held, the printing came out
looking pretty good. And, after drying
for just a few seconds, it was
both clearly visible and fairly indelible.
I could rub the text, and it didn’t
smear or come off on my fingers.
Now that I had a proof of concept,
it was time for some brainstorming on
a mechanism with my favorite machinist and fellow roboteer, Rick Abbot.
could bring something over. He
showed up on my doorstep with the
Wow! The device was a beautifully
rendered Rube Golbergian masterpiece crafted from clear Lucite and aluminum. It was festooned with servos,
linkages, push rods, and even an ammo
“hopper” made from a five gallon water
bottle with a gear motor driven agitator
(Figure 6). The agitator had dual vertical
rods held together with a dome shaped
brace so it could stir up the ping pong
ball ammo and make sure there was
always a ball ready to drop (Figure 7).
Below the hopper was a loading
tube managed by a servo motor
controlled “indexer”(Figure 8). The servo
was attached to a rotating disk to extend
and retract two rods in the path of the
ping pong balls. It had two simple, mutually exclusive positions: load and release.
In the load position, the upper rod
is retracted, allowing a single ball to fall
down into the loading tube that is
stopped from falling through by the
■ FIGURE 5. Inkjet printed text
on spinart card.
SODA AND SKETCHES
I lured Rick to a meeting at my
house and stuffed him with soda pop
and tortilla chips while I sketched out a
design for a ping pong ball
printer on the white board. He
nodded sagely, made some
notes and said he might be able
to come up with “something” in
a bit. He left with a few ping
pong balls, a couple of servos,
and the serial inkjet kit.
About a week went by,
and I got a call from Rick asking
if I might be available so he
lower rod. In release position, the upper
rod is extended to block the load tube
from the rest of the balls in the hopper
while the lower rod retracts releasing
one ball to fall down to the next stage.
Once a ball falls down the tube, it
comes to rest on a small aluminum
pedestal that was topped with a
rubber o-ring for both traction and
■ FIGURE 6. PingPongPrinter
prototype (shown here with
agitator removed and placed
in the foreground for clarity).
■ FIGURE 7.
February 2008 15