For the Junior Stars’ show Coal, which is about the Elf who is in charge of the Naughty List, I created this beautiful Naughty List Tracker…

The story involves Coal the elf feeling pretty sad about all the kids on the naughty list, and a little bit guilty perhaps that it’s his fault, so he devises a scheme to pitch a 3-strike program to Santa, to give kids a couple chances to do better.

Among the props and constructions for this show, this was the most interesting one, it was running quietly in the background through the second half of the show.  It’s design is based on flip-clocks, which are surprisingly expensive and don’t come in very large sizes.  These flippers were cut from quartered cardstock sheets, with (mostly) random names printed in a script font on them.

Each card had to be split in half and attached with a long wire “hinge” to cardboard tube rollers with small hinge wheels to hold each card like a rolodex.  A small wire catch at the top of each opening keeps one card in place at a time, until the roller drags it down far enough that it flips and the next card is displayed.

The flippers are powered by continuous motion speed-controllable servos and the “strikes” are flipped by 12 individual mini servos, which are controlled by a single PWM controller card and microcontroller.  The program is designed to randomly process multiple name and strike changes based on a simple set of rules.  There is no external control for this peice, though it is powered by an external supply to avoid the weight and short lifespans of alkaline batteries in a motor-heavy application such as this.

If we stage Coal again someday, I will double the size of everything, when I began 11 inches seemed more than big enough for the name cards, and poster-sized foam board too, but the effect would be more spectacular twice as big and no change would be needed to the number of motors or circuitry.

Here’s a closer, if less eventful video.  Most of the time this tracker was supposed to be rather quiet so as not to distract from the performers, I had to take a lot of short clips of nothing happening to get some good action shots.