Since we just used to Sensor Test tool to verify that all of the sensors onboard the KK2.1 flight controller are functioning as expected, we will now need to calibrate the accelerometer.
Ready for one more bit of theory before we are done programming the KK2.1? I think it is worth knowing a bit about how accelerometers work before we calibrate the one on the flight control board. First of all, accelerometers are devices that sense acceleration forces. They can detect two different types of acceleration: static acceleration forces caused by the Earth’s gravity, and dynamic acceleration forces caused by movement. So when we calibrate our accelerometer, we are giving it a zero reference so that the sensor knows what direction is down (the direction of gravity).
The KK2.1 can then talk to the accelerometer to figure out which direction is down and it can combine this information with data from the gyroscope, and data about the quadcopter’s movement-related acceleration to determine exactly how the quadcopter is oriented in three-dimensional space.
Let’s calibrate the accelerometer. The most critical part of this process is setting up our calibration environment correctly. In order to calibrate our accelerometer, we need the quadcopter to be completely level and on a solid surface. So, using a bubble level, find some solid surface in your work area that is completely level. It is worth the extra effort to make sure the surface is level because if you calibrate your accelerometers while the quadcopter is in a non-level position, your quadcopter will probably drift around in the air, making it more difficult to fly. Avoid using a wiggly table or a swiveling stool or something because if you quadcopter moves during the accelerometer calibration process it will throw off the accuracy of the calibration.
So, place the quadcopter on your chosen level surface. Then, in the KK2.1 menu, scroll down to the ACC Calibration tool, and click the Enter button. The KK2.1 will tell you to place the quadcopter on a level surface, which we’ve done already, so press the Enter button again. The KK2.1 will then go through the calibration process, which takes eight seconds or so. Make sure you do not bump the quadcopter or the table during this process. And finally, the calibrated accelerometer readings will be displayed.