I was inspired by Frits Lyneborg's Yellow Drum Machine. Watching the videos, it has such personality! I have also been thinking recently about sound and robotics. I did some research looking for a version of the robot that used the Arduino as a brain, but couldn't find one that seemed so responsive and alive as Frits' version.
Step 1: Creating a stable base
For the robot base, I used a Six Leg Walking Gearbox Kit # 21-135, which is available from several different sources. Here's one source: http://www.jpmsupply.com/servlet/the-658/Gearbox,-Walking,-Elenco,-Kit,/Detail .
I had previously created an Arduino-based robot that used an h-bridge motor control chip to run the motors. It also has a 6volt 1000mAH rechargeable NiCad battery that was rectangular and flat for power. But that's all it had.
I love spheres, so I took an acrylic Christmas tree ornament from Hobby Lobby and cut a hole in the bottom to pass wires through. I used 1 1/2 inch #6 bolts and nuts as standoffs to hold the sphere above the six-legged base.
But once I created the first hi-hat stick, I realized that I had no stable place to attach it to.
I had some 1/8 inch thick plastic sheet laying round, so I marked out a stretched hexagon to use as the base. I cut it out with a dremel and a plastic cutting blade. I attached it to the base with #6 machine screws. The base has some places that will take a machine screw.