Motus Reference Manual
Page 45 of 146
Version 1.1
29/11/2019
are automatically saved internally.
11.5.2.2
Using the Packet Protocol
1. The unit should be powered on and the vehicle kept stationary.
2. After power on wait 5 minutes for the temperature and filter to stabilise.
3. Ensure that the device has a position fix, either from an external GNSS receiver,
or using the External Position and Velocity packet #44 or the External Position
packet #45, before proceeding.
4. Send the Magnetic Calibration Configuration Packet with the action Start 3D
Magnetic Calibration. The following steps 5, 6 and 7 can be performed in any
order.
5. Slowly rotate the vehicle twice around the X axis (roll).
6. Slowly rotate the vehicle twice around the Y axis (pitch).
7. Slowly rotate the vehicle twice around the Z axis (heading)
8. Read the Magnetic Calibration Status Packet to ensure that the calibration
completed successfully. If not successful, send the Magnetic Calibration
Configuration Packet with the action Cancel, wait 2 minutes and repeat from
step 4.
11.5.3
Automatic Magnetic Calibration
Automatic magnetic calibration is an algorithm that continuously and automatically
calibrates for static magnetic interference. Automatic magnetic calibration is enabled
by default and it is recommended to keep it enabled for all vehicle types. When used
on top of a 2D or 3D calibration it can give the best results from magnetic heading.
Every time Motus is powered on in a cold start (48 hours without power) the automatic
calibration is reset. The automatic magnetic calibration starts operating when Motus is
travelling at a speed over 5 m/s with a GNSS fix and velocity heading turned on.
Automatic magnetic calibration is not as accurate as 2D or 3D calibration, however it
is sufficient for most vehicles and allows Motus to be installed into vehicles and
operated without user intervention. Automatic magnetic calibration can be turned off
using the Filter Options dialogue in Motus Manager, see section 12.8.2.
11.5.4
Disabling Magnetometers
In situations where there is very strong dynamic magnetic disturbances present, it is
recommended to disable the magnetometers. When the magnetometers are disabled
a secondary heading source is required otherwise may become inaccurate. Velocity
heading is the recommended source. Please see section 11.4 for information on
heading sources. The magnetometers can be disabled using the Filter Options dialogue
in Motus Manager, see section 12.8.2.
11.6
Data Anti Aliasing
Internally Motus's filters update at 1000 Hz. When Motus outputs data, most
applications require the data at a much lower rate (typically < 100 Hz). This causes a
