Nuts and Volts - February 2008

PERSONAL ROBOTICS

■ FIGURE 3. Parallax serial inkjet printing kit.

■ 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 PingPongPrinter Prototype.

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.