THE EGGBOT CHALLENGE
Following the tradition of cracking eggs in celebration of Easter in Greece with the game of tsougrisma (τσουγκρισμα in Greek) we decided to build an EggBot that could robotically draw intricate designs that we fielded from our client partners and staff.
So what’s an EggBot? It’s a machine capable of drawing on spherical or ellipsoidal surfaces. You might say, a pen plotter for spherical coordinates. Or a simple but unusual CNC machine, ripe for hacking. Or an educational robot– and you’d be right on all accounts. It’s worthwhile to point out that there’s actually quite a bit of history here in this project. The EggBot kit is the result of our collaboration with Bruce Shapiro, Ben Trombley, and Brian Schmalz. Bruce designed the first Eggbot back in 1990, and there’s been a process of continuous evolution ever since.
The Eggbot kit includes Brian Schmalz’s EiBotBoard (EBB), which includes a USB interface and dual microstepping bipolar stepper driver. With its 16X microstepping and the 200 step/rev motors, we get a resolution of 3200 steps/revolution in each axis. The EBB also controls the little servo motor that raises and lowers the pen arm. In previous versions of the EggBot kit, raising and lowering the pen has usually been done with a solenoid. But the servo motor allows very small, precise motion to raise and lower the pen over the surface. The end of the pen arm is hinged with an acetal flexure for precise bending, and the pen arm clamp fits ultra fine Sharpie pens and many others.
And the results? Pretty good. The objects shown here include golf balls, eggs, Christmas ornaments, and light bulbs… besides we had an egg-cellent time in the process.