MultiWii PRO w/MTK GPS Module (HobbyKing) MAG drift on tilt

[Weezul]

Hey guys,

I have a problem with the MAG sensor on the MultiWii PRO Flight Controller that HK offers. I have not added the GPS yet. The symptoms are as follow (I can also make a video if required):

I noticed when arming and powering up, that the front right, and rear left motor gets much more power from the board than the other two. Kind of like it tries to correct yaw. I then checked the MAG, calibrated it using the config tool, but noticed that even after that, the more throttle I give (No props, the quad is standing motionless on the table) the more the compass heading changes, when I give less, it changes back again. My first thought was motor interference. However, when it is not armed, and there is no motor activity (Even battery disconnected, powered only by USB), I still get wild compass changes when tilting the quad on both its roll and pitch axis. The compass deviations are not random, it really moves along with the quad, just not the way it is supposed to.

The MAG sensor on the board is the HMC5883. Now, in the config.h file I selected the board "HK_MultiWii_328P" instead of the seperate sensors. Could this be the problem? (I did this, as when enabling the separate sensors the reaction time was sluggish).

Any advice on fixing the compass?

Thanks!

[Weezul]

The more I think about it, the more I get the feeling that the MAG sensor is orientated incorrectly. I read that the HMC5883L is a "3-axis digital" compass. Since it is 3-axis... and digital, this might mean that I can fix this in code somewhere. Still, the MultiWii pro is a relatively popular board, someone must have had this problem. Am I googling the wrong terms?

[Noctaro]

Hi,
did you follow the magnetometer calibration routine as mentioned in the wiki?
-> http://www.multiwii.com/wiki/index.php? ... alibration

It seems your calibration went wrong. Once its calibrated, think of shielding it if you still get an offset at powering your motors.

I do not know your board, but you may check the orientation by comparing to this.
-> http://www.multiwii.com/faq#How_should_ ... directions

Hope that helped.
Greetz Noc

[scrat]

The more I think about it, the more I get the feeling that the MAG sensor is orientated incorrectly. I read that the HMC5883L is a "3-axis digital" compass. Since it is 3-axis... and digital, this might mean that I can fix this in code somewhere. Still, the MultiWii pro is a relatively popular board, someone must have had this problem. Am I googling the wrong terms?

Why do you have MAG turned on when taking of? Take of in acro mode and then try to turn on MAG and check behaviour of the copter.

[Weezul]

Thanks for the replies. I managed to solve the problem last night. I went back to step one, changing everything in the config header back again. Strangely, this time with the right board selected I had no "lag" or sluggish responses from the board. I must have uploaded without saving, or saving something with an incorrect setting or something before.

To answer some quetions for other people reading this later. I did do the calibration according to the wiki, but since the board was reading data from the wrong sensors (Getting GYRO and seeing it as ACC input) the MAG sensor was thrown off, and calibration had no effect.

About taking off with MAG on, I have not taken off yet, it was just standing on the table with the motors spinning (no props). Thanks for the tip however, since I no doubt would have been taking off with the MAG on.