Nuts and Volts - September 2008

■ FIGURE 8. The Cowlacious ST-200b kit and color manual.

■ FIGURE 9. Tin snips used to remove a small part that blocks the mounting bracket.

■ FIGURE 10. Rotary tool used to smooth out the servo bracket mounting spot.

to take home. Of course, having some experts on hand (i.e., my buddies from The Robot Group) certainly doesn’t hurt since they can help troubleshoot any issues that arise. A Make and Take is a lot of fun and is very effective in both learning new things and getting things done.

After my announcement on the mailing list, I counted up the RSVPs and it looked like we had about 10 folks from all around central Texas that wanted to make talking skulls, with some folks signing up to build a pair! To meet the demand (and to make sure I had one for myself), I ordered 12 complete Cowlacious Talking Skull kits with red LED eyes. (Note: See the Resources section to order a kit for yourself in time for Halloween!)

The weekend of the Make and Take arrived and we set up the center island in my kitchen as the “skull prep” area (Figure 5). The kitchen table was set up with three soldering stations for circuit board assembly (Figure 6). We also had some speakers and a small MP3 player for testing the finished units (Figure 7).

I opened the kits and was happy to see that each one was bundled with a full-color multi-page instruction guide (Figure 8). If you’d like to have a look, the instruction books are available directly from Cowlacious (see Resources) as PDF documents. The booklet had detailed instructions and photographs on how to modify the fourth class Bucky skull to hold the servo motor and allow a piece of piano wire to reach the jaw. There were also detailed step-by-step instructions on how to assemble the audio servo board in a separate color booklet. As you can

see in the photos, we were all using these guides constantly as we went along and they were VERY helpful!

Though the skull modification guide is very detailed, the actual modification is fairly simple and can be recapped in short order: A small piece of plastic is “snipped” away from the bottom of the skull to make room for the servo bracket mounting screw (Figure 9). A rotary tool is used to smooth an area inside the skull for the servo bracket (Figure 10). The springs that hold the jaw to the skull are removed, then holes are drilled in the skull to allow clear plastic wire ties to act as hinges for the jaw (Figure 11). The servo bracket is attached to the skull with a nut and bolt (Figure 12) and then a hole is drilled to allow the piece of stiff wire (i.e., piano wire) to be threaded from the servo down to the jaw (Figure 13). Finish by attaching the servo horn to the servo (Figure 14) and you have a modified skull ready to go (Figure 15).

Smoke Test!

While some folks were busy modifying the skulls, the soldering area was in full swing (Figure 16). The first board was completed by Paul Atkinson (Figure 17) and we took it to the test area to try it out. We powered it up and uh, oh, the servo refused to budge! After a bit of head scratching, connection testing, and taking readings on the board using a meter and an oscilloscope (Figure 18), we found that two pads on the circuit board had a solder bridge. Once that was fixed, the board worked fine.