This page contains tips for overcoming common issues when using the navX-MXP together with the National Instrument RoboRIO.
navX-MXP is reset due to a RoboRIO Stage 2 Brownout
As described in RoboRio Brownout and Understanding Current Draw, the RoboRIO will remove power from the MXP connector if the unregulated Input Voltage (VIN) to the RoboRIO drops below 6.3VDC.
Thus, if the navX -MXP is connected to the RoboRIO via the MXP connector and a Stage 2 brownout occurs, the navX-MXP will shutdown until the RoboRIO VIN voltage is again > 6.3VDC.
If the navX-MXP power input is removed during operation this will cause a yaw angle discontinuity – since the currently calculated yaw angle is based upon in-memory calibration coefficients.
Fortunately, the navx-MXP has a USB input, and has on-board circuitry to automatically switch over to the USB input for power and a capacitor to ride-over the switching period. A comprehensive way to allow the navX-MXP to continue to operate even in the face of a RobRio Stage 2 brownout is to modify a power-only USB connector (5VDC and ground leads only), and connect it to one of the VRM’s 5VDC outputs. The VRM buck/boost regulator configuration allows it to provide 5VDC down to a VIN of 3.6V, by which time the RoboRIO would have completely shutdown.
Using this approach, the navX-MXP will continue to be powered even when the RoboRIO VIN drops below the level where the RoboRIO has completely shutdown (Stage 3).
No power to navX-MXP when plugged into the RoboRIO MXP Port
This case can occur when one of the MXP Expansion sets of pins has become shorted. An indication of this case is that the POWER led on the RoboRIO will go red, indicating a short on one of it’s power rails.
To resolve this issue, inspect each set of Expansion IO pins, and look for a ground pin being shorted to either a power or a signal pin.
To protect against accidental shorts, Kauai Labs recommends a protective enclosure that at least partially encases the MXP I/O pins, such as the “lid”-style enclosure created for the navX-MXP.
USB: Verify USB Serial Port Binding
If connecting the RoboRIO to the navX-MXP via one of the RoboRIO USB host ports, verify that the navX-MXP’s USB interface is correctly bound to RoboRIO Serial Port ASRL3:INTR, as shown below.
This information is displayed in the RoboRIO’s webdashboard. For instance, if you have connected your RoboRIO to your PC via USB cable (connected to the RoboRIO’s USB Device Port), the web dashboard can be viewed within a web browser (in this case, at http://172.22.11.2).

