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The inertial measurement unit is an electronic device that can measure and report the specific gravity and angular rate of an object to which it is attached. In UAVs, the IMU provides crucial data that helps the drone/plane to be self-aware of its stands, heading, and speedmovement, so it is one of the most basic sensors on a drone.
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Measures the acceleration force applied on the three axes of the sensor
Could tell the orientation of the drone. Say if the drone is placed levelly on the ground, then the acceleration it is experiencing is zero, except for the z-axis, which is experiencing gravity. If the 1g acceleration is shifted to the y-axis, then we know the drone rotates 90 degrees by its y-axis
The acceleration can be further computed to produce velocity and displacement
Can be used to sensor-fusing with the GPS data to provide more accurate position information
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A compass, that tells the absolute heading of the object
This is useful when we want to know where the drone is heading on a map. Without a magnetometer, we are able to can know if the drone is moving, but we can’t tell if it is going north or west.
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Drone Dancing (IMU calibration)
If you've ever joined participated in a flight flying test before, what you had a high chance have seeing before is a person chances are good that you've seen someone, or a couple of people, holding the drone and attempting to get it oriented in all directions. Is this mysterious WARG ritual that can bring us success in the flight test? Yes to some extent, doing a drone dance does help the drone perform better in the flight. The motivation behind the drone dance is actually IMU calibration, or more specifically, the drone , and trying to orientate the drone in every direction. (WIP)dance is the calibration process of the magnetometer.
Calibration process for each sensor:
Accelerometers: place the sensor in different directions
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Gyroscope: it gets self-calibrated quickly, and usually doesn’t need to move the sensor around to finish the calibration
Magnetometer: the most cumbersome calibration. For a magnetometer to sense the Earth’s magnetic field correctly, it needs to remove the magnetic field effect caused by the magnetic materials from the aircraft body and the electronics on board. The calibration requires the sensor to be mounted on the aircraft and rotates the aircraft to different angles until the sensor figures out the correction parameters.
Further Reading
References:
https://www.vectornav.com/resources/inertial-navigation-primer
https://ardupilot.org/copter/docs/common-accelerometer-calibration.html
https://ardupilot.org/copter/docs/common-compass-calibration-in-mission-planner.html#