Brownout behavior - alternative design goals

[jhersh]

Originally Posted by Tom Line

If I understand what you're saying I have to disagree. We found this issue during alpha in our 2013 hilo. We use a string pot for positioning, and the drop out would cause the pot to report a low position. That sent our hilo up. So non Incrementing sensors still create problems when they brown out.

Hi Tom,

I think this is a perfect example of where your robot has a better chance to operate reliably using the new functionality, but the control software needs to pay attention to the info available. Since you are not losing absolute position and the motor is disabled, the likely cause for the behavior you saw was a combination of integral windup and reading the sensor in a non-ratiometric way. Naturally as the voltage of the 5V supply drops the lower the resolution of the reading.

The roboRIO Power API will tell you what the voltage of the reference rail is so you can divide. There is also a new potentiometer API that does this for you. The Power API also tells you when the brown-out level has been crossed so you can pause your control loop until it has recovered. The Power API also tells you when the 5V supply has blacked out (though I did notice a bug in this in the LV API implementation that I'll fix for next season), so you can stop believing your sensor at that point. This will always be below the brown-out level, so your control loop should already be paused.