If the VMX-pi default yaw axis orientation isn’t sufficient for your needs, you can use the OmniMount feature to re-configure the VMX-pi yaw axis, allowing high-accuracy yaw axis readings when VMX-pi is mounted horizontally, vertically, or even upside down.

In certain cases, the VMX-pi axes (Board Frame) may not be oriented exactly as that of the Robot (Body Frame).   For instance, if the VMX-pi circuit board is mounted sideways, the navX-Micro axes will not be oriented identically to the Robot.  This configuration is shown in the diagram below:


Transforming VMX-pi Board Frame to Body Frame with OmniMount

VMX-pi’s “OmniMount” feature can transform the VMX-pi X, Y and Z axis sensor data (Board Frame) into Robot Orientation (Body Frame) by detecting which of its three axes is perpendicular to the earth’s surface.

This is similar to how a modern smart phone will rotate the display based upon the phone’s orientation.  However unlike a smart phone, the OmniMount detection of orientation does not happen all the time – since the orientation should not change while the robot is moving.  Rather, each time OmniMount configuration occurs, VMX-pi records this transformation in persistent flash memory, and will continue to perform this transformation until the transform is reconfigured.

To configure OmniMount, follow these simple steps:

  • Install VMX-pi onto your robot. ENSURE that one of the VMX-pi axes (as shown on the VMX-pi circuit board) is perpendicular to the earth’s surface.  This axis will become the yaw (Z) axis.  Note that this axis can either be pointing away from the earth’s surface, or  towards the earth’s surface.
  • Press the ‘CAL’ button on the VMX-pi Circuit board AND HOLD THE BUTTON DOWN FOR AT LEAST 5 SECONDS.
  • Release the ‘CAL’ button, and verify that the orange ‘CAL’ light flashes for 1 second and then turns off.
  • Press the ‘RESET’ button on the VMX-pi circuit board, causing it to restart.
  • The VMX-pi circuit board will now begin OmniMount auto-calibration. During this auto-calibration period, the orange ‘CAL’ LED will flash repeatedly.  This process takes approximately 15 seconds, and requires two things:
    • 1.  During auto-calibration, one of the VMX-pi axes MUST be perpendicular to the earth’s surface.
    • 2.  During auto-calibration, the VMX-pi must be held still.
    • If either of the above conditions is not true, the ‘CAL’ LED will be flashing quickly, indicating an error.  To resolve this error, you must ensure that conditions 1 and 2 are met, at which point the ‘CAL’ LED will begin flashing slowly, indicating calibration is underway.
  • Once the VMX-pi auto-calibration is complete, the Board Frame to Body Frame Transform will be stored persistently into VMX-pi flash memory and used until auto-calibration is run once again.