|After playing around with the base of a bulldozer toy I decided to build my own chasis. I used the canonical circular base with differential drive wheels, a very simple yet robust design for an indoor 'bot. This design makes the movement of the 'bot symetrical, eliminating certain highly non-trivial problems like parallel parking. The brain is a nice Parallax Basic Stamp II, well suited for simple robots. It is programmed from an ancient XT laptop which otherwise would be a rather ugly paperweight.|
I have been very pleased with the current chasis. It has plenty of room for expansion, and allows several nice features like hard mounted on/off switch, reset button, power indicator LED (blue!) and 9-pin female serial connection. The last makes hooking it up for programming it a breeze (as compared to the rather delicate connector on the StampII expansion board). Around the edge of both wood disks are two copper strips used as a power bus.
To detect colisions I needed a bumper skirt. A common material for this is transparent acrylic, which has the added bonus of being IR transparent. I couldn't find a properly sized cyindrical mold to shape it with (28 cm diameter is hard to find) so I had to create my own. Three layers of 1/2" plywood seperated by sections of copper pipe, bolted together with a nice handle and copper plate on the outside. It worked great as a mold, if slightly over-engineered. I found the easiest way to soften the acrylic was to hold it over a stove burner on high. Wait until that section is soft, then push it onto the mold with gloves. A damp rag helps hurry the setting process. Be careful not to touch the acrylic to the burner, for it is rather flammable.
|Seen here, the bot has four bumper sensors (two offset in front, two offset in the rear), photocell light level sensors, and a temporarily mounted polaroid sonar transducer. Unfortunately the acrylic bumper skirt isn't mounted yet because the original rubber band system proved unreliable. Eventually the bot will also have IR proximity sensors, multiple photocells on the circumference, focused photocell on the underbody to detect surface changes, microphone and pyroelectric sensor for detecting human body range heat sources.
This is an actual image, the surface it is on is my enigmatic hexidecimal carpet from Ikea. Someday I'll type it in and see if it means anything. I'm hoping it is the designer's public key.
Maybe someday I'll create an easy to read schematic, but the design changes so often that it would be a pain to keep up to date.