DF Fans,
We had planned and prepared for a really important presentation and SAVS demo scheduled for this morning at 8:30. I had gone over and tested every part of the system a half dozen times in preparation, and as usual the DF's performance had been predicatably rock solid. The meeting was postponed until 2:00PM, and at about 3:00PM we walked outside to a hot dirt parking lot for the big climax of the presentation - a flight demo. And in perfect accordance with Murphy's Law, the SAVS refused to respond in any way. It would not arm, nor vary the red LED in response to throttle after turning on - nothing.

I had experienced similar behavior once before, on a very hot 94-degree day, and made the mistake of taking off anyway, once I managed to get it armed. In mid-flight it suddenly tipped up and dove straight for the ground. Luckily it was still responding to stick commands and I managed to get it straightened out. So I figured it had something to do with the afternoon heat and on a hunch I set it under a bush for a few minutes. It then fired up OK, and I took a chance and flew the demo:

http://www.youtube.com/watch?v=JA14lf0oPbA

SO HERE'S THE PROBLEM: The microcontroller (44-pin SMT component on the right side of the main board) will begin to run erratically above a certain temperature. With the ambient temp being above 85 or 90 degrees, the floor temperature of the IC is raised closer to its limit. If the controller is exposed to DIRECT SUNLIGHT, it will exceed this temperature and fail (temporarily). I verified this theory by turning on the DF in my garage, and verifying LED response to the throttle. I then placed it outside with the sun shining directly on the right side, and in 2 minutes it stopped responding to the throttle. Bringing it back into the shade, it took only about 15 seconds for the controller to come alive again. I reconfirmed this by spraying compressed air on the controller after it had failed in direct sunlight, and it immediately came back to life due to the cooling. This is a simple set of tests that should be conducted independently, on the off chance that the microcontroller on my board just has a bad solder connection.

Some of the behavior of the controller on the margins of heat failure sound a lot like the unexplainable glitching and Ti weirdness that some people have experienced here. The solution - paint the inside of the clear canopy with silver paint to turn it into a mirror and reflect the sun's heat. Guess it never gets that hot in Minnesota or Saskatoon!

- Bruce