Basic Line Following

[tatwood]

This thread is about basic line following and involves a simple course with gentle turns. Robot magazine is delighted that the pioneering gang at Chibots, the Chicago Robot Club, has offered to help orient our forum members with advice and comments based on their extensive experience in this arena.

I'd like to open the discussion with the following question, but any relevant question is fair game for any who wish to join this thread. One of our readers asked us to set up a basic line following track and to test several line following robots in a race to see which are the fastest machines. I'd like to know: what are the dimensions and characteristics of the course, what is the best medium to create the line, how fast are the best competitors, and are there any sure-fire best platforms/sensor combos to start with? Thanking in advance any who comment--

Tom Atwood
toma@botmag.com

[hassenplug]

So many questions. If you want to make a line following robot, before you can test the robot, you need a course. I've entered many competitions, and they all have slightly different rules. That means I need a different test course for each event.

The solution I've found is to use "white-board" material (not exactly sure what it's called). I picked up a 4x8 ft piece for about $10. Then, you can layout the course with black electrical tape.

I'm always a bit nervous, because Chibots events use a black surface, with a white line, while all the others use a white surface with a black line. So, all my testing is done on a white course. However, I just have to reverse the compare statements for it to work on a black course.

I think the board is either white-board (dry-erase) material, or shower board. It's slick, so the tape can be pulled off pretty easily.

To make it a bit easier to move around my house, I actually cut the board into two pieces. One is 4x5 and the other is 3x4. If I want to do a little testing, I bring out the small board.

One thing to remember while laying out the electrical tape is to avoid stretching it. It may be fine for a while, but it will pull itself out of shape in the long run. Unroll it, let it "unstretch" then lay it down.

I usually try to make the course as hard as the rules allow. That way I know my robot can make it through the course.

One of the real tricky challenges for a line following robot is an "s" curve. It may overshoot a little on the first turn, and a lot on the second. So you should always include one of those in your test track.

Steve

[jkjellman]

At Chibots we run our BLF contests on a custom built elevated platform one of our members made (thanks Don!) to help aid in setup. The course surface is composed of Armstrong Imperial 51910 floor tiles. The line is made from 3/4" white electrical tape.

Each tile has a pre-made line on one or both sides. There are corners, straights, diagonals, intersections, etc. This way our course is built just before the contest by laying out the tiles like a giant puzzle.

For those that want to practice at home, you can purchase a small quantity of these tiles from larger Home Depot stores and build a track on any hard surface.

Hope this helps.

Take care,
KJohn

[wrighthobbies]

One thing to remember while laying out the electrical tape is to avoid stretching it. It may be fine for a while, but it will pull itself out of shape in the long run. Unroll it, let it "unstretch" then lay it down.



Steve, this holds true with the Armstrong tiles too. If the tape is stretched, it can cause the tiles to cup slightly.

Just take your time when laying down the line.

[wrighthobbies]

I'd like to open the discussion with the following question, but any relevant question is fair game for any who wish to join this thread. One of our readers asked us to set up a basic line following track and to test several line following robots in a race to see which are the fastest machines. I'd like to know: what are the dimensions and characteristics of the course, what is the best medium to create the line, how fast are the best competitors, and are there any sure-fire best platforms/sensor combos to start with?

At Chibots, we have at least 3 people that have line followers capable of over 1M/sec average speeds. One is built with Legos, the other 2 are built from scratch. Several members have had good success with Lego line followers.

For top performance, you should reduce the mass as much as possible. Mass is not your friend when it comes to fast line followers. The mass of the bot should also be balanced or offloaded so it doesn't impact the robot's responsiveness. Steve Hassenplug uses a chariot-like design that moved the Lego controller's mass onto a small cart pulled behind the drive/steering wheels. This makes the bot able to respond quickly and not have to push the mass of the controller back and forth. Dave Cook balanced the mass of his bot over the drive axle, minimizing the force needed to steer it. I used articulated frame steering to turn the bot so the drive motors kept in motion and reduced the power needed to force the turns.

I am fond of the GP2S40 sensors for line following. They are extremely small but have a decent focal length of 3mm to 6mm.

[TheDuck]

I have an image in my mind of how big the course is based on your descriptions of the tiles or boards you use for competition and testing. I'm wondering, how big, on average, are the robots that are in these competitions? And is that governed by rules or practicality?

[wrighthobbies]

Chibots original size limitation was 8.5" x 11" which was easy to test by using a piece of paper. There is some discussion of changing the size but nothing definitive yet.

For practical purposes, a robot should be smaller than the tile size, which is 12" x 12". Larger bots could detect nearby lines and cause erroneous behavior.