This page summarizes the recommended best practices when integrating VMX-pi with a robot, such as a FIRST FRC robot. Following these best practices will help ensure high reliability and consistent operation.
Excessive vibration will reduce the quality of VMX-pi orientation sensor measurements. The VMX-pi circuit board should be mounted in such a way that it as firmly attached to the robot chassis.
2) Understand and Plan for Calibration
Gyro/Accelerometer Calibration is vital to achieving high-quality VMX-pi IMU readings. Be sure to understand this process, and ensure that it completes successfully each time you use the robot.
If your robot moves during calibration, or if noticeable temperature changes occur during calibration, the calibration process may take longer than normal.
Using the VMX-pi yaw angle before calibration completes may result in errors in robot control. To avoid this situation, your robot software should verify that calibration has completed before using VMX-pi IMU data.
3) Protect the Circuitry
VMX-pi contains sensitive circuitry. The VMX-pi circuit board should be handled carefully.
An enclosure is recommended to protect the VMX-pi circuit board from excessive handling, “swarf”, electro-static discharge (ESD) and other elements that could potentially damage VMX-pi circuitry.
5) Provide a “Zero Yaw” feature (for Field-Oriented Drive)
The VMX-pi gyro “yaw” angle will drift over time (approximately 1 degree/minute). While this does not normally impact the robot during a typical FRC match, if using field-oriented drive during extended practice sessions it may be necessary to periodically “zero” the yaw. Drivers should be provided a simple way (e.g., a joystick button) with which to zero the yaw.
6) If possible, mount VMX-pi near the center of rotation
Since VMX-pi measures rotation, errors in the measured angles can occur if VMX-pi is mounted at a point not near the robot center of rotation. For optimal results, VMX-pi should be mounted at the robot’s center of rotation. If VMX-pi cannot be mounted near the robot’s center of rotation, the offset from the center of rotation can be used to correct the yaw angle.
7) Use OmniMount if VMX-pi is not mounted horizontally
By default, VMX-pi’s motion processing requires the unit be mounted horizontally, parallel to the earth’s surface; the yaw (Z) axis should be perpendicular to the earths surface.
If you need to mount VMX-pi vertically or upside-down, you will need to enable the “OmniMount” feature in order to get reliable, accurate yaw (Z) axis readings.
8) Learn how the sensor behaves by using the navXUI
The navXUI provides insight into the key VMX-pi IMU features, and can help debug issues you may encounter when integrating VMX-pi onto your robot. Running this user interface is highly recommended for anyone using VMX-pi.