June 2017
Document 1000-4126 - FSM300 Tare Function Usage Guide - Revision 1.1
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This Tare setting allows the user to choose which of the rotation vector outputs to use
as the basis for the Tare. In most cases, Rotation Vector is the correct choice here. If
you are using the Game Rotation Vector as your main input, and you want to tare the Z
rotation to re-center the Game Rotation Vector to point north, then you’d need to use
the Game Rotation Vector as the basis for the tare. Likewise, if you were doing a full
tare using the Geomagnetic Rotation Vector, then you would need to use that as the
basis.
Tare Procedure
Using the options defined above, you can choose what type of tare configuration makes the most sense
for your application. Here are a few examples of typical configurations:
Device First Time Setup
In this example, the FSM300 is installed in an HMD and the sensor orientation needs to be
defined. This could be performed at the factory or by the user at first time setup. This will use a full tare
across all 3 axes and also save the setting into flash using the Persist Tare function. Note that because
the Pitch and Roll axes are being tared, the procedure is dependent on the device’s orientation relative
to North so follow steps 3-5 carefully.
1.
Power on the FSM300 and activate the Rotation Vector sensor.
2.
Calibrate the magnetometer by rotating the device in a figure 8.
a.
To validate that the magnetometer is well calibrated, you can look at the
Rotation Vector’s Accuracy Estimate field. This value provides an estimate for
how accurate the algorithm thinks it is in units of radians. A good goal is to
confirm that the Accuracy Estimate is <10 degrees (0.1745 radians). If
performing a Figure 8 motion does not reduce the accuracy estimate below 10
degrees than move to a cleaner magnetic environment.
3.
Calibrate the accelerometer by positioning the device in 4-6 unique orientations and
ensuring the device is stable for a few seconds in each orientation.
a.
One way to think about this is to imagine the device is a cube and set it down on
each face (upside down, right side, left side, on its front, its back).
4.
Set the device down for a few seconds so that the gyroscope ZRO can calibrate as well.
5.
Determine North in your current environment.
a.
You can either look at a physical compass, or look at the Rotation Vector to
determine where North is. When the Rotation Vector reads W=1, X=0, Y=0, Z=0
the device is pointed North.
6.
Position the device so that your desired forward direction is pointed North and make
sure the device is level.
7.
Run the Tare Now command with the following settings:
Byte
Name
Value
Description
