What’s all this number stuff?
Collecting the calibration numbers can be quite intimidating at first. This section tries to give you an idea what they are used for, in the hope it will make the collection process less bothersome.
The programs Cal and Sim3 create 81 values from the static and dynamic logs that you have gathered.
There are 3 sensor groups — the gyros, the accelerometers, and the magnetometers — and each have an X, Y and Z axis. So there are 9 data points affecting everything the calculations do.
The values generatet correct for the manufacturing differences of each sensor, how accurately they are mounted, temperature effects, and how they are affected by external influences like wires, ESCs, motors, etc.
Each sensor axis has a Bias value and a Scale value for each axis. These values vary with temperature, so the programs Cal and Sim3 try to find 3 numbers that best fit a 3rd order polynomial equation that represents the corrections needed over the operating temperature range. There are temperature corrections for Bias for all three axis’ on all three sensors. There are also corrections for Scale for the accs and mags. Since the gyros would require some sort of calibrated rate of change, the Scale is taken from the manufacturer’s data sheet.
So, if you’ve been calculating all this, we’re up to 63 different values. 24 each for accel and 24 for the mags. Only 15 for the gyros since we leave out the scale temperature calibration and only apply the bias temperature calibration.
The define names clearly explain what each value is used for. If you look closer at the source code, you can see how they are skillfully applied.
Currently, more accurate gyro bias values are generated on AQ startup, so those values are not used at this time, but the temperature corrections are being applied.
There are also 18 values created that correct for the slight misalignment of the sensors. That brings it up to 81, and with Magnetic Inclination and Declination we get a rousing 83 values that will make the AQ fly better than its competitors… if we generate good numbers!
The proprietary programs Cal and Sim3 are used to take all the data provided, sometimes leveraging one against the other to come up with a unique set of numbers for each board’s installation.
The idea is simple, the more accurate the data, the better the machine will fly.