"Digging this up in a search for info on soft-iron magnetometer distortion. I gather that it is theoretically possible to calibrate for soft iron distortion... it's just not easy to do from what I can tell. Per Freescale app note. If only I…"

"Don't worry about it. The cod ewill handle it. The yaw axis is stabilized by the Magnetometer. Or else get a real compass and calibrate it with your eye. Right or left or only is up to you...:)"

"attached is my self test data(10sets each for positive and negative bias). however if an equal and oppositie field is applied, data should be relatively equal. but u can notice that the data for negative bias is much lower. therefore i don't…"

"I did scale factor first. JI"

"oh what i did was added some delay and poll for drdy to become 1 but it's still the same(inconsistent). are u getting consistent scale factors?"

"Yes, I did, and it's not correct. I added a 10 msce delay between the i2c setup steps to allow the self test bias to settle out and it seems to have solved the problem. Looks like some magnetometers need more setup times than others. John"

"hi john, i tried the self test but every time it gave me different reading, as i result i obtain very different scale factors. does that happen to you? it ranges from 0.9 to 8"

"I tried something, in ground start, when we initialize the offsets, I do: Read_adc_raw(); for(int y=0; y<=2; y++) // Read first initial ADC values for offset. { AN_OFFSET[y]=0; } for(int y=3; y<=5; y++) // Read first initial ADC values for…"

"Bill, Thank you very much for the explanations, I understand that your algorithm cancels the magnetic offset around the compass in the moving frame. I was testing the algorithm with a magnet because I will have the IMU closed in a little space with…"

"John and Christophe, One more thought on the subject of magnetometer calibration...the algorithm that I published is for offset removal only, it is not for soft-iron compensation. If you are using the algorithm for offset removal, it will not…"

"John and Christophe, One more comment about the algorithm that I described: It relies on the assumption that the gyros, the magnetometer, and the magnetic interference physically move together in lock step. That way the algorithm can distinguish…"

"Hi Christophe, The algorithm that I posted for removing offsets works best if the offsets do not change in time. In that case, the offsets can be removed automatically in flight. There is a short "learning period". Each time the airframe…"

"John, From what I understand from Bill P's post, this method should have a good heading even when the motors turn, but when I test this by putting a magnet near the IMU the magnetometer and the yaw both drift a lot! It does this when I put the…"

"Christophe, When the magnetomter is initialized, it is run thru a self test as desribed in the HMC5843 datasheet. This should output a specific set of numbers. The difference between these readings and their theoretical value (715 the way I set up…"

"John, I'm looking at your code and I have a few questions: - Are you calibrating the magnetometer bias at each start of the IMU? It seems so, I thought this only had to be done from time to time. Can you tell me why it is done everytime? What…"

"Hi John, Thank you, I'll look at your code today :) Christophe"