RE: Science Olympiad
It's going to be tough for the contest directors to make it fair and protect the kids from cheating if the setups are what it sounds like. I'm sure they chose brushed motors because of cost and to eliminate having to install a speed controller. But it's not clear how they determine if the batteries are legal. The only true 9v battery is an alkaline, as NiCd's go to 9.6, LiFe's 9.9 and other lithiums higher than that. They would do better to simply decide on a specific battery and motor the kids have to use and make it all about the car design. A NiCd car pack with a motor that makes good use of it would keep costs down and would give the kids a level playing field. If the school was inclined the invest in the chargers, going to a 3 cell lipo would give them more power to play with.