During the summer of 2000 I had the opportunity to build a Mindstorms robot for the Minnesota FIRST LEGO League . The robot was used as part of an interactive exhibit in the Wonders of Technology building at the 2000 Minnesota State Fair . As this was in a booth shared by the Science Museum of Minnesota, the robot was built to to loosely model a champsosaur from their 'After The Dinosaurs Were Gone' exhibit. The robot has the basic shape of a crocodile with the RCX built into the body. It is a narrow tracked design with two extra idler wheels inside each track to move the track-to-floor contact points closer together. This enables the bot to turn more quickly and easily yet still retain most of the stability of a tracked vehicle as it only rocks forward and backward a very small amount. A third motor is used to operate the jaw so it can 'eat'. There are three light sensors. Two face down for following a 'river' (a 5" wide blue line) and there is one in the mouth for detecting 'food' (foam balls). There are also five touch sensors. Each leg has one touch sensor and the fifth is configured as a limit switch for detecting when the jaw is open all the way. The closing strength of the jaw is limited by a 24T clutch gear. For the interactive exhibit, it was programmed to follow the 'river' when initially either set on the river or pointed in a direction that will cross it. When it reaches the end of the 'river' it opens it's mouth, makes the ascending notes sound, and expects to be fed. After being fed it turns around and heads off to the other end of the 'river'. It then opens it's mouth and expects the 'food' to be removed. It turns around and repeats this fetch cycle until switched off or someone bumps it's legs. Bumping either of the front legs while it is following the 'river' will trigger the same feeding response as the end of the 'river'. Bumping either of the rear legs will cause the bot to quickly turn around to 'see' what was bothering it, then it will continue on it's way again. It also uses the ascending notes sound to say "feed me" and the descending notes sound to say "um, I guess I'm not hungry". It also beeps at whoever disturbed it by bumping it's back legs. Two of these robots took turns entertaining people 12 hours a day for the 12 day run of the fair. The total distance traveled was estimated somewhere around 36 miles! I had a wonderful time watching kids feed it but I was told the most common comment by adults was that it must be following something magnetic in the table. :-)
This first set of pictures is of the initial prototype.
Click on any image for a larger view.
Champsobots from space! ... ok, just the 'river' on my driveway before it had surrounding landscape details added.
Champobot Instruction set .
A few extra notes :
The two robots used at the fair were partially glued together to withstand *lots* of handling. This was done in sections so that sensors, motors, and other moving parts could be replaced if needed (although replacing parts proved unnecessary as nothing broke). A couple extra tricks were needed to enable the robot to work in the continually changing ambient light environment. The first was modifying the 'food' light sensor to make it more sensitive by removing the red LED and replacing it with two diodes in series. The phototransistor was also encased in heat shrink tubing to block the small amount of light received though the sides of the light sensor case. This modification enabled the 'food' to occlude ambient light without reflecting any from the sensor itself. A 1x2 Technic beam (not shown in the instructions) also helped accomplish this by using the hole through the beam to narrow the view of the sensor. Along the same lines, plastic washers were glued to the downward facing light sensors to block the effects of reflected sunlight from overhead windows. One really handy aspect of the final version was routing the wires to enable battery replacement without disconnecting any wiring.
Robolab version 1.5 was used for programming the champsosaur.
Click here for an image of the Robolab program used.