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Unread 11-21-2017, 06:48 PM
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Re: Breaker Modeling

Quote:
Originally Posted by phurley67 View Post
But that means we would be slower/less powerful/etc than someone else who pushes the envelope. Our auto shifting 6 cim drive train would easily exceeded the current limit for short periods of time. We also had code that monitored how long we were above a calibrated max current level and would force a downshift, and a second monitor that would kill the drive motors if we exceeded it (that never happened in play), with the assumption it is better to lose a battle, than to trip a main breaker and be out for a match. Those calibrated values were educated guesses made based on these charts, some math, and real world experience.

All of that said, under the RoboRIO, we were far more likely to experience brown outs, and adjusting everything to avoid/minimize brownouts will make it very unlikely to ever trip the main breaker. We ran test runs, adjusted motor ramping, current limits, etc until under abusive driving conditions with a fresh battery, brownouts were very rare and when they did occur they were of the very short variety. This combined with a fairly smart auto-downshift, and a traction limited low gear; we did not have any issues with the main breaker all season.
With ALL things equal (including your driver's driving style/strategy), allowing higher motor currents might give you an advantage. Of course, all things are not really equal so it is possible to have a robot with lower motor currents outperform one with higher motor currents.

It will be better for teams to implement current limit through the motor controller than to have the breakers open, even the snap action ones in the PDP. Pushing the envelope, as you are suggesting, might give you 5-10% more peak current, for periods of 1 second or less, but you will have a greater risk of opening a breaker. It also makes you vulnerable to variations in factors such as the ambient temperature and part-to-part variations (breakers are not tightly calibrated). Will that slightly higher peak motor current really make a measurable difference in your performance? Is the risk of opening a breaker acceptable to your strategy? Can you devise a way to get better overall performance by not pushing the motor power envelope so hard so you can have reliable power? Why are you allowing abusive driving conditions? The sustained high current draw conditions will wear out your batteries faster.
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