[Ken Streeter]

Originally Posted by Ken Streeter

The reason I ask is that about 4 years ago I built an incredible line follower where the secret wasn't in the software but was in the construction of the lego robot. Do you have freedom to choose your own robot design?

Even though I haven't heard back after my note from yesterday, I decided I'd provide a little more info. In my opinion, the real trick to getting incredible line following ability is to use a "steering robot", like a car, rather than like a typical FRC robot which typically uses "tank-style" differential drive to turn.

In a line-following steering robot, the light sensor is actually mounted to pivot with the front wheels as they turn. In this way, the light sensor ensures that the front wheels track down the line. Whenever the robot is driving with the light sensor over the edge of the line, the front wheels get centered over the edge of the line, pointing the front tires in the correct direction along the line due to the geometry between the light sensors and the front wheels.

After building a robot like this, play with things you can do to tighten the steering response (you want no slop) and adjust the distance between the light sensor and the front wheels. You'll want the robot to be as small and light as possible. The programming is actually rather simple -- use the steering to keep the sensor centered over the edge of the line, and simply power the drive motor to keep the robot moving. Use of proportional control for the steering would probably be sufficient, but PD would probably improve the steering. PID would probably not be needed in this case. In addition to modifying the steering software, you can adjust the forward speed to be greater when the robot is "tracking well" and slower when it is "tracking poorly."

The robot that I built as a line follower a few years ago was an enhancement upon an incredible line follower by Gas Jansson -- his famous "Steerbot" -- http://www.lugnet.com/~726/SteerBot His page describes a lot about how the robot is built, includes detailed photos, and talks about the programming. There are also some great videos of the robot driving at http://www.lugnet.com/org/us/smart/~48/meetings/2001/01

My improvements were never documented, but had to do with decreasing the slop between the steering motor and the front tires, as well as slop between the front tires and the light sensor. (Gus' robot has a fair bit of play there, which decreases the responsiveness of the system.) I'd love to show you a picture or photo, but the robot was cannibalized for my FLL team before I took the time to take photos.

Let us know how it turns out!