Understanding the Alignment of the V5 Inertial Sensor – VEX Library

The Inertial Sensor is a combination of a 3-axis (X, Y, and Z) accelerometer and a 3-axis gyroscope. It allows for very accurate measurement of roll and pitch. However, a few inertial sensors can show significant error for roll and pitch when placed on a level surface.

This procedure calibrates the accelerometers in the Inertial Sensor and saves the result in nonvolatile memory. This procedure needs VEXos 1.0.10 or later.

Checking your V5 Inertial Sensor to see if it's out of alignment

V5 Brain is shown with a V5 Inertial Sensor connected to one of its Smart Ports. The Inertial Sensor is level on both axes.

To check if the inertial sensor is out of alignment, place the Inertial Sensor on a level surface that is known to be level in both axes. Be sure the sensor’s V5 Smart Port and a V5 Brain’s Smart Port are connected with a V5 Smart Cable.

Brain screen is shown in the Home menu with the Devices option highlighted.

Turn on the V5 Brain and touch the ‘Devices’ icon.

Brain screen is shown in the Device Info menu which has a list of all of the Brain's Smart Ports and connected devices. The Inertial Sensor icon in the Device Info menu is highlighted to indicate that it can be selected to open its information menu.

Touch the Inertial Sensor icon on the Device Info screen (V5 Dashboard).

If the Inertial Sensor is showing angles for roll and/or pitch that are larger than 1 or 2 degrees it will need to be re-calibrated.

Note: Only perform the following calibration if your V5 Inertial Sensor is showing angles for roll and/or pitch that are outside of acceptable limits (1 or 2 degrees).

Realigning your V5 Inertial Sensor

V5 Inertial Sensor is shown attached to a VEX C channel piece with a spirit level placed next to it. The spirit level's bubble is pointing directly upwards, indicating that the Structure piece and the surface below it are level.

To realign your V5 Inertial Sensor, attach the sensor to a VEX structure (C channel etc) and place it on a stable and level surface. Use a spirit level to ensure the surface is level. Do not attempt to do this procedure with the sensor mounted on the robot.

Note: ensure to check that the Inertial Sensor is level in both the pitch and roll direction.

Brain screen is shown in the Inertial Sensor menu that lists the sensor's data. The Calibrate button has a red background and a label reading Factory, and it is highlighted.

Open the V5 dashboard, press and hold the calibrate button on the dashboard for about 10 seconds, it will turn red and show the word “Factory” next to the calibrate label, stop touching the V5 screen when the button turns red.

Brain screen is shown in the Inertial Sensor menu that lists the sensor's data. The Pitch in degrees and Roll in degrees values are highlighted, and in this example the Pitch reads 0.03 and the Roll reads 0.17.

Touch the red calibrate button again, the Inertial Sensor will calibrate for about 2 seconds and then return to the normal dashboard screen. Values for the accelerometer, roll and pitch should now show normal values for an Inertial Sensor on a level surface.

This calibration only needs to be performed if the sensor has an error in roll and/or pitch. It is not something to do on a regular basis. It does not need to be performed during normal use of the sensor. Once calibrated, it is very unlikely you would ever need to calibrate the sensor in this way again.

Warning: Constant use of this procedure may potentially damage the sensor.