Date:  10/4 - 2014 & 14/4 - 2014Duration of activity: 2 x 7 hours
Group members participating:  Alexander Rasmussen, Søren Gregersen, Søren Ditlev

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Robot Race

Goal  

To build a robot that can complete the Alishan train track in the fastest possible time.

Plan

We plan to use 2 light sensors to follow the black line on the Alishan track, these two sensors should make it possible to follow and discover the black line.

First off we will make a simple implementation of a line follower[1], and then expand it to use 2 sensors. When we get that working we will try to implement a pid controller and see how that works. Once the system is able to drive following a line we plan to implement tacho counters to keep track of when the system should turn left, right and 180. This should be done concurrently so that the tacho counter will overrule the the line follower. Once the system is turned  the system should be able to relocate and follow the the line again. Finally a color sensor mounted in front of the system will be able to detect the green field and make the system stop.

Results

We managed to get the simple line follower working with two sensors, however it was really slow and made a lot of oscillations, this was due to the simple implementation of the line follower that we used. So in an attempt to avoid these oscillations, we tried to implement the PID controller, by making the car move forward if both light sensors detected white surface, and then adjust when one of the sensors reached the line. This did not work out as we had planned since the system still oscillated a lot and was very slow.

The approach with two light sensors accompanying each other, might not be the best way to implement a line follower, it looks like they will always be trying to move the car towards each other and therefore the two pid’s would works against each other making the system highly likely to start oscillating.
A better approach might be to just use a color sensor for the line following part since we need it for stopping in the goal zone anyway and we know from previous lessons that it can move fairly fast[2].

Result = ∞ infinity

Conclusion

We tried to make a pid line follower with 2 light sensors, but the  systems oscillated a lot and was very slow. We used a lot of effort to try and correct the PID line follower, but we could not seem to get it work satisfactory. The problem we kept coming back to had to do with implementation of two light sensors. The PID counter for each of the sensors affected the other sensor forcing the system to turn constantly. Since we are able to solve this problem we did not not move on to solve the next problem, making the car turn at the correct places on the Alistar train track and thus did not complete the the track.        

References

[1] http://legolab.cs.au.dk/DigitalControl.dir/NXT/Lesson1.dir/LineFollower.java

[2] Video of a fast PID LineFollower: ]http://www.youtube.com/watch?