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PID Line Follower

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  • #16
    Re: PID Line Follower

    The best line following LEGO robot I've ever built had a single steerable front wheel. The light sensor was mounted on a spar in front of the wheel and you could "tune" the line following by moving the sensor closer or further from the wheel. Even with a dumb "bang-bang" controller on the RCX it followed lines better than anything I've seen since. Geometry is far more important than algorithm and most FLL robots have lousy line following geometry. Mounting the light sensor along the centerline is helpful. If you can't mount the sensor in the center you can compensate by using different scaling for left and right corrections.

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    • #17
      Re: PID Line Follower

      Originally posted by Dean Hystad View Post
      The best line following LEGO robot I've ever built had a single steerable front wheel. The light sensor was mounted on a spar in front of the wheel and you could "tune" the line following by moving the sensor closer or further from the wheel.
      We had a line following competition locally in the off season last year, and the winner did exactly that. I had a 4wd ackerman steering robot (thanks, Sariel's book!) that couldn't even approach the speed.
      Coach, FLL Team 3146 Peace By Piece 2013 - 2016; Team 29410 The Dragon Bots 2016
      Judge, FTC 2014-2015; Field Technical Advisor, FTC 2016

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      • #18
        Re: PID Line Follower

        Do you have any videos or pictures of it? I am trying to picture in my mind how something like this would work, but coming up short.
        Regards,
        Skip Morrow

        2016 Animal Allies
        2015 Trash Trek
        2014 World Class Learning

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        • #19
          Re: PID Line Follower

          Imagine a tricycle with a broom handle attached to the handle bars, parallel to the front wheel. When you steer the wheel the sensor sweeps side to side very quickly, even if the robot isn't moving forward.

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          • #20
            Re: PID Line Follower

            A good example (if out of focus) on Youtube: https://youtu.be/14PswDr0otE
            So instead of the usual two separately powered wheels and a unpowered caster wheel, the caster wheel steers and both of the other wheels drive with one motor (Ideally through a differential, but a locked axle works for demonstration). The control program swivels the caster so the forward placed light sensor is on the line, the rest of the robot follows.
            Coach, FLL Team 3146 Peace By Piece 2013 - 2016; Team 29410 The Dragon Bots 2016
            Judge, FTC 2014-2015; Field Technical Advisor, FTC 2016

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            • #21
              Re: PID Line Follower

              Originally posted by shelbydavis View Post
              A good example (if out of focus) on Youtube: https://youtu.be/14PswDr0otE
              So instead of the usual two separately powered wheels and a unpowered caster wheel, the caster wheel steers and both of the other wheels drive with one motor (Ideally through a differential, but a locked axle works for demonstration). The control program swivels the caster so the forward placed light sensor is on the line, the rest of the robot follows.
              I watched the first half of the video, but the robot looks like it has two powered front wheels and a caster wheel in the back. Is that the correct video link?

              As an aside, it was fun to watch the robot try to navigate the obstacles and maze in addition to following the line. It would be fun to have the referees drop a LEGO wall at a random spot on the far side of the board as an obstacle to the advanced teams.

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