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Originally Posted by Joe Johnson
I agree with 80-90% of what Matt has to say, but the above quoted comment is one that I feel I need to say something about.
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This is not to say that there are not multiple reasons NOT to use N motors per side -- there are many, but tripping the 120 Amp breaker is not one of them (imho).
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Sit right back folks, it's story time from Matt Adams.
Sit, honest. This might get long.
I'm rehashing one of my very first posts (my very first?) and this reply made by Dr. Joe.
First off, I'd like to say that I absolutely respect Dr. Joe and many of the brilliant things that he's shared with the first community through Chief Delphi and other venues. He's a brilliant guy. When he said the above statement back several months ago, I really appreciated the engineering experience instead of the theoretical calculations I do in school. I used that advice while doing calculations for our machine, and we didn't have a single problem with our 120 Amp breaker over the course of the entire season, minus a single match. That single match is why I'm posting now.
Let me immediately remark that I am in no way trying to put any blame on Dr. Joe for the success or lacktherof of 461 this season. Ultimately any sort of machine failures are the responsibility of the design engineers and the people who give designs the stamp of approval (or signature in our case). That person was me.
With that all said...
461 had 4 motors (no transmission) for their drive train this past year, as well as a few supplimental motors to control other functions, namely a fisher price for a small ball roller and a van door for a big ball grabber.
The reason I post now is to share some more real-life experience using this breaker, in hopes that similar mistakes are not made in the future.
Curie Field, 2004. Last match of the division finals. 461 had played at least 8 consecutive matches without swapping out with an alliance member for strategic reasons... both joysticks were pushed forward, and the robot does too... for about 5 seconds after autonomous before tripping the 120 Amp breaker... costing the alliance the match and perhaps winning the division or more.
The 120 Amp breakers are thermal devices... over the course of several matches, they heat up, and become more likely to trip. While several teams know to use compressed air to cool motors during the final rounds, most teams don't think about the main breaker. If you're pulling 160 amps or so through it for several consecutive matches, this is an important fact to remember.
The FIRST finals are truly a test for machines, and all of the design parameters need to be built around this. From personal experience, there's no feeling worse than losing a match because of a human error or an obvious potential failure that wasn't planned for. I hope that everyone who reads this post ensures they think carefully about power management, thermal conditions of their machine, and designing machines around their shining moments in the finals.
Good luck everybody!
Matt