Plan for RoboRIO Brownouts [FRC-specific]

The RoboRIO contains circuitry to remove power from the RoboRIO MXP and Onboard I2C connectors when it detects an input voltage drop below a certain voltage level; this is known as a Stage 2 brownout. While brownouts do not typically occur during a FRC match (since fresh batteries are typically used at these times), during extended practice matches brownouts are common. If the robot drive train draws large amounts of current, even for a short time, brownouts could potentially occur even with a competition FRC match.

navX-sensors maintain state information that will be reset when the navX-sensor circuit board is restarted. Avoiding navX-sensor restarts is very important if your robot software uses the “yaw” angle.

Fortunately, the RoboRIO provides just such a power supply, since its onboard USB interface is powered by a boost regulator which will provide 5V of power even when the RoboRIO input voltage (VIN) drops as low as 4.4 volts (once the RoboRIO VIN drops lower than this, the RoboRIO itself will restart). navX-sensors provide a secondary power supply, and will automatically switch to that power supply if ever the I2C connector power supply is not present.

Thus to address this situation, simply connect a USB cable from the navX-sensor circuit board to the RoboRIO; if a brownout does occur, the navX-sensor circuit board will automatically switch to use power from the RoboRIO’s USB port.