[Al Skierkiewicz]

Guys,
The question is "how many batteries will we need?" The simple answer is this...a robot that can run 3-4 matches on a battery charge can get by with four.(Ask around for teams that could supply a spare if needed.) A robot that drains a battery in one match will need 3 to 4 times that number, either owned or borrowed.
The 3-4 match rule of thumb is for designers at the beginning of build. A robot that runs a battery down in one match is dangerously close to running out of power before the match ends, i.e. no reserve. As to actual current drawn and trying to predict what the battery will deliver, there is no way to predict. Each match is different and there is so many other variables it is impossible to try. Suffice it to say that these are the real world constants you should consider...
1. The battery can deliver over 400 amps but not at 12 volts.
2. The 120 amp breaker can sustain 600% over current for a few seconds without tripping. (It is a temperature controlled device.)
3. The 18 amp hour rating is at less than two amps load current. When drawing in excess of one hundred amps expect that to exponentially decrease. I estimate that one match robots pull the 18 AH down to let's see 36 amp minutes.
4. The amp/hour rating is based on terminal voltage of 8 volts. When a heavy use team draws high current, the battery will allow robot function down to about 6-7 volts before the controller quits sending PWM. When the terminal voltage rises again, the robot works for a little while longer.
5. Most high current robots, draw max current in turns, so if there is little turning, the current is much lower.

I will try to cover more of this in a presentation at nationals. Let me know if there is anything else you want me to discuss.
Al