[DaveF]

We saw quite a bit of this at a VRC tournament yesterday where I served as the Field Manager. I am not sure what programming template and field control system is used for Savage Soccer, but we were running the VRC template and using the standard VEX field control system with crystals. The teams having this problem were complaining that the field control system was operating erratically and causing the robots to go back into autonomous mode during driver control. It was my understanding a couple years ago, and I do not believe VEX has changed anything in the last year or two, that once your robot runs the autonomous part of the template, it cannot re-run autonomous until the power on the robot is cycled to reset the microprocessor. The field control system cannot cycle your robot’s power or tell it to run autonomous again.

The programming template sits and waits to see a radio signal from your transmitter before autonomous starts. When we start the match, all the transmitters (sitting on the floor with power on, but no radio signal transmitted) are enabled for a period of time to start the running of the autonomous portion of your code (radio signal transmitted). Once the autonomous code is running, your transmitter is then disabled. Once driver control starts, the transmitters are re-enabled, so you can drive, until the match ends. No data from the field control system is transmitted through your transmitter to eh robot. All the field control system does is enable the transmitters to produce a radio signal.

So after that long description…. I started watching the robots very closely that repeatedly had problems yesterday. Many of them had 6 to 10 motors on them, and they were running many of them at the same time. The second before the robot would revert back to autonomous mode, the robot microcontroller would produce a low battery indication (red LED blink). What appeared to be happening is that the current drain on the battery was causing the battery voltage to drop below the minimum needed for the microprocessor to run (around5 V ?), and the microprocessor would shut down, motors would stop running, the battery voltage would recover, and the microprocessor would reset. It would see the transmitter signal and start autonomous all over again. You must remember that to measure true battery voltage (to determine if it is properly charged) the battery must be under load. When a battery is loaded more than its capacity and charge can handle, the battery voltage will drop quite significantly. You also say that it worked fine off the field. I bet that when you were testing off the field, you were not making your robot work as hard (pushing and doing other activities that make motors work harder and draw mor current). So you were probably not drawing enough current to cause a battery voltage sag.

So the bottom line is that I believe that at the VRC event, some teams were not vigilant about keeping batteries charged, and some were assuming that if they measure the voltage of the battery and it showed 7 volts (not under load) it was ready to go. At the VRC event these problems increased as the day went on yesterday- which probably coincides with teams showing up with well charged batteries, and having trouble getting one fully charged by the end of the day due t match schedules. In addition some teams have been using their batteries for upwards of 3 years, and their ability hold a good solid charge has diminished with age. To keep the VEX batteries usable longer, I know some teams have been using battery conditioners on them.

After all of that, I recommend you check your battery situation very closely. Good luck.