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Except the thermal calibration, all this steps are necessary to achieve = assisted modes using the INS13 (GPS Navigation) attitude e= stimation algorithm, also called EKF (Extended Kalman Filter).=
High-quality GPS receivers can provide around 3.5 meters horizontal accu= racy. Higher accuracy required for GPS Navigation is attainable by using GP= S in combination with augmentation systems. For instance additional inertia= sensors. Centimeter accuracy systems such as RTK are not yet supported. Ad= ditional inertia sensors such as accelerometer, gyroscope, magnetometer, ba= rometer are absolute minimum of non-redundant information required for navi= gation.
All sensors calibrated and properly functioning are blended by sensor fu= sion algorithm (i.e Extended Kalman Filter) to yield a more accurate estima= te of a position. Before attempting to use GPS navigation, aircraft must fl= y perfect with Complementary fusion algorithm, all sensors must be calibrat= ed, functional and giving good data. Although Extended Kalman Filter (EKF) = is designed to deal with noise, it can only tolerate certain level of contr= adicting prediction data. Failure of any inertia sensors in most cases rend= ers whole system not flyable.
Great video about sensor calibration from Eric:
This step is optional, but highly recommended. It reduces Accelerometer/= Gyro or Barometer drift.
During this step the controller monitor temperature changes while warm u= p and record the sensor values. At end the controller compute curves that c= ompensate drift for every sensor within the temperature range used for cali= bration. No need a -40=C2=B0C > +80=C2=B0C range, but temperature calibr= ation should be done at working temperature while flying in normal conditio= ns.
Remove the bag from the freezer, connect the USB cable to the computer, = wait the connection and start the thermal calibration with the Start button= .
Recommendations
Avoid lamp use for warming, barometer sensor is very sensible to light !=
While the controller warm up, just keep the board still= , close to a heat source like a radiator.
Thermal calibration can be saved for this board see UAV Settings Import-Export page.
Because Accelerometer sensor measure gravity, Home Location need to be s= et first. Please look the Setting Home location= page.
This calibration should give a best accuracy so controller know his real= orientation in space. Calibration adjust Accel bias but also Accel scales.=
This calibration should be done while the controller is unmounted on fra= me, a controller case is preferred and allow accurate/stable positions.
The controller can be adjoined against a box for best positio= n.
To initiate the Accelerometer calibration, press the Start button. Follo= w the onscreen instructions, orienting the controller as shown and pressing= Save Position .
On every step= when the position is saved, the controller need to be perfectly still !
After calibra= tion is successful, save calibration results with Save button.
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Accelerometer= s calibration result can be displayed on UAVOBrowser: accel_bias and accel_= scale.
Prior to magnetometer calibration, the Home Location need to be set, ple= ase look the Setting Home location page.
Using the know location and the World = Mag Model data , the controller computes the Mag vector expected.
Be sure the controller is mounted on frame in his final configuration, p= ower wires twisted and away from unwanted electromagnetic fields.
To initiate the magnetometer calibration, = press the Start button. Follow the onscreen instructions, orienting the con= troller as shown and pressing Save Position at each step. There is no= need to align the vehicle exactly south, north, east or west during the in= dividual steps. The directions indicated serve only to tell you in which di= rection the airframe should be positioned relative to some point. One can s= imply assume that North is in front of you, East is to the right, West is t= o the left and South is pointing at you.
Another method consist on validate t= he five first steps, move/rotate vehicle on all axis and finally save the l= ast step.
Calibration should be performed outdoors, Oplink or Bluetooth conn= ection give best results.
After m= ag calibration is successful, save calibration results with Save bu= tton.
To initiate the Board Level Calibration, place the vehicle on a flat, le= vel surface and press the Start button.
Follow the onscreen instructions, doing the two measurements.
Save Position each time when it is perfectly still.
After level c= alibration is successful, save calibration results with Save button= .
Virtual Attitude
If you are using a custom virtual board orientation (Roll or Pitch) be s= ure you set and save values prior to this level calibration.
This step will allow you to calibrat= e the gyro measured value when the board is steady.
To perform the calibration leave the=
board/airframe completely stationary and press Start.
After gyroscope calibration is successful, save cali= bration results with Save button.