Date: 15th and 16th of April 2013
Participating group members: Kennekt Baagøe, Morten D. Bech and Thomas Winding
Activity duration: 4 hours

Goal
To make the robot drive the rest of the way of the Alishan track, as described in the previous post, we have already reached the top, but have not made it back down.

Plan
Continue our where we left off at “Update: Lesson 7”, and start by making a simple inverse of the uphill program to make it go downhill.

Progress
As mentioned in the previous blog, Update: Lesson 7, we had a 90% chance of getting the robot to drive all the way to the top of the track and turn 180 degrees there. The trip takes around 18 seconds which is relatively slow, which is most likely due to the way we handle the corners in a “stop at first corner – turn – move – stop – turn – move up next slope” way instead of a continued motion.

When we arrived at Zuse Monday someone had moved the track into a different room, and unfortunately this has made the track a little different from when we were testing on it on Saturday as most of the slopes are now crooked. The changes made it very hard for us to make the robot drive all the way to the top as the crooked nature of the slopes meant that the robot would drift either left or right when it was supposed to move straight ahead. We had some success, but we were reduced to a chance of 30-35% of reaching the top every time.

So when we reached the top we had hope that the robot would make it downhill correctly, which it unfortunately didn’t and we had to apply some small changes to our downhill algorithm, first error was not to listen for the first black line seen but it should be the second instead which made the robot turn right right after it left the top. Finally we had to adjust the angles to turn and length to be driven, but with the low chances of getting to the top from the starting point, it took a lot of time to see if the changes we made were correct or not.

Another change we made was not to drive by distance on the plateaus but instead looking for lines in the hope of making the line of attack of the next straight run more precise. However this didn’t work that well either. One of the reason for that was that even now we place in almost the same position at the start point it didn’t see the line in the same place on the plateau every time. Basically we couldn’t drive in a straight line and as mentioned in the previous post, Update: Lesson 7, we tried to overcome this by getting two motors which match each other well in terms of speed and rotational accuracy, but this did not solve it because of the crooked slopes as mentioned earlier.

Finally we had a run where the robot got almost all the way to the finish as well – unfortunately it drove off the side on the last straight stretch, but it did manage to touch the green part with one wheel and color sensor which made it stop. After several attempt afterwards to replicate the run with a small change for the last straight stretch we throw in the towel and wouldn’t have a time for the contest. Unfortunately we were not recording when we got this best attempt at completion. The video below is how far we managed to get when recording.

Conclusion
In theory the sequential solution should be the fastest way to do complete the track, however it relies on so many variables, like the mentioned moving of the track and subsequent crooked slopes, it becomes very hard to implement and we had to spend a lot of time on small details which we might have been able to avoid using, eg. a line following robot instead or if we had been able to get a reliable heading which we tried to do with the sensors mentioned in the post Lesson 7.