SciBorg: Day 2 -- Feedback and Control


Part C: Working with Fixed Distances
For the second part/day with the SciBorgs, we started with a program telling our SciBorg, Aurora, to drive 10 feet (Part C). Having noted how much of counta and countb we would need to compensate for each motor, this activity went rather smoothly. We concluded that, from the Day 1, that signaling the motors to stop when countb equaled 975 equated to roughly 38.9 inches. As 10 feet equates to 120 in, we multiplied by the ratio 120/39, or 3.07, and set the signal for when countb is greater than 3000. Initially, Aurora -- the SciBorg -- was just a hair away from the finish line. We increased the signal for countb to 3005, and we were spot on! We did not have a large problem with skidding or slipping; Only on the ramp did I noticed an increased speed but slower spinning of the wheels (which should not correlate).

Part C II: Adding Sensors
In adding sensors mechanisms -- touch, ultrasonic, and brightness -- we found the perfect combination with the touch and ultrasonic sensors the best. With both of them, our test runs were consistent and came to closest to the barrier set by the tape measure itself. Separated:
  • The touch sensor was very reliable and always came as close as possible to the specified distance.
  • The ultrasonic sensor was most successful when it was triggered to stop 6 inches away, so we always had to extend the tape out. 
  • The brightness sensor was not as effective and could be skewed easily -- and having worked with light sensors before, it's a pain to calibrate them. However, when they work, they work wonderfully, usually under uniform lighting.

Part D: Understanding Surfaces
For the straight-bang-bang program, Aurora was quite consistent in its driving, on low-friction surfaces (Lab Floor) and even high-friction surfaces (Carpet). (Low-friction surfaces, however, present the best results.) However, with a single wheel, the princess car struggled a lot with a high-friction surface. On the plus side, she formed a barely curved path. Going up the ramp, Aurora had some difficulty, both in having a smooth drive and driving straight, and, on her way down, Aurora skidded and slipped more noticeably. 

Part E: Line Following
Boy, was this a doozy! Somewhat like the LegoCar project, it took numerous iterations to actually form a functioning SciBorg -- and lots of help from others. Pinpointing every exact turn and bend tripped me up several times. I found that reduction of speed (to 90) helps considerably, and, after comparing the values of brightness in several conditions, found our "magic trigger" to be when the sensor read less than 550. A video of the testing to come soon! Go Aurora!

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