More bugs than I need

By | September 15, 2012

For a few weeks now, I have been struggling with strange behaviour on the micromouse. This version is Decimus 2C. It is the build that ran (poorly) at the UK contest in the summer of 2012. It did not do well so I have been trying to get it all tidy for the Taiwan contest next week.

For a while now, the micromouse would just do strange things. Particularly at start up, it would sometimes veer off to one side. Whenever I tried to find out what was wrong, it would behave just fine. Then, it would sometimes just crash into a wall for no apparent reason. Now, all the clues were there but I had forgotten the most basic of fault finding rules and overlooked the hardware. A close inspection of the board soon revealed the cause:

A dry joint on the motor connector for micromouse Decimus 2C

A classic dry joint on the motor connector. Normally, there is some opaque teflon tape over these pins so I had not noticed it before. It seems incredible that a pin could get all the way through that tiny gap and fail to make contact but it did. It didn’t take long to put it right:

A repaired dry joint on the motor connector for micromouse Decimus 2C

Now, of course, everything that I did in the software to try and find and eliminate the error is suspect and I may have been doing more harm than good.

While looking for data to support the odd behaviour, I recorded the mouse position, profiler speed and the speed as recorded by the wheel encoders. A record is taken on every control cycle. That is every millisecond. position is in mm. Speeds are in encoder counts per millisecond. The encoder speed is just the sum of the left and right encoder counts taken straight out of the counters. Acceleration is set to 3m/s/s and the position is the where in a cell, the mouse is. So, after one cell of travel, the position resets. It does not go to zero because of the way I do things. That is not the problem. Have a look at the data:

Strange encoder behaviour on Decimus 2C

For some reason,  whenever I reset the mouse position at the end of a cell, I get a glitch in the encoder counts. I have no idea why but it is not going to be good. Looks like another late night.

2 thoughts on “More bugs than I need

  1. Galen

    Hi Peter,

    Have you considered using some type of source revision software? If you
    are not currently using one, I suggest git or svn. I’ll admit that it is hard
    getting into the habit of using it, but the benefits quickly show themselves.

  2. Peter Harrison Post author

    I use git to track all my code. What I really need though is more discipline and a good methodology. Frequently, I find that I have mixed up several modifications into one feature branch for example.

    Also, the current version of MPLAB is based on Netbeans which I like. not least because it retains a separate file revision history allowing me to look at previous revisions of files and keep track of casual edits.

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