Monday, January 23, 2012

aBot – Maiden Voyage

Time for an update…

Tonight, I ran a short test.  The plan was to go in a straight line for five seconds and then stop.  Unfortunately, while I was successful with the go, the five seconds and stop the straight line didn’t quite work.

Over the last three and a half weeks have been busy with a lot of things.  However, I did manage to squeeze in some time to work on the new wheel encoders for aBot.  During this time I made several discoveries that have shaped the design.
  1. I found out that the output from the LM339 is an uncommitted collector and therefore I need pull up resistors on the digital input pins.
  2. I determined that unused comparator pins should be grounded.
  3. I discover that in order to get a clean digital signal I needed to implement hysteresis with the LM339.  This consisted of adding two additional resistors to the design so that the comparator wouldn’t cycle at the set point causing numerous interrupts until the voltage rises enough that it constantly stays above the set point. 

That brings us to tonight’s test.  Below are two pictures of aBot at the time of the test.  It wasn’t pretty but it was functional.

As I said at the start of the post aBot ran and stopped according to plan.  What didn’t work was running in a straight line.  The problem was that during the 5 second run aBot’s left wheel travelled 31 inches while the right travelled 33 inches.

If the wheel encoders and the software monitoring them was working right this shouldn’t happen.  So now it is back to troubleshooting to find out where the problem is.