External magnetometer on APM 2.0?

I'd like some opinions on the viability of adding an external magnetometer for use with the APM 2.0 purple kit I'm installing on my 600EFL. 

The problem I am trying to overcome is interference from the Neu 1917 in-runner I have in my heli. When in the mission planner I can calibrate the mag and get good readings near the motor, consistent and accurate to ~10 degrees, however when I spin up the motor (rotor head off of course) I can watch the mag loose it's accurate bearing no doubt due to the coils in the motor charging/discharging. Rather than relocate my APM, I would like to install an external mag on the tail of the heli. Then I would have to sort out how to ignore the internal mag and substitute the external mag's signal.

Is it viable?

Want to help me figure it out :-)

BTW the GPS does just fine this close to the motor...

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Replies

  • It appears that on the 2.5 they only cut the SDA line, should have occured to me that if you don't initialize the on-board 5883L that it wouldn't be sending any info on the I2C or tripping the DRDY either.... some time I feel like I'm lucky to tie my own shoes LOL.

    I'm also sure that they are not using DRDY on the external mag either :-)

    So, cut SDA and use the external I2C.... simple. If you were really handy I imagine you could even flow solder over your cut if you cleaned the trace and cut right at the via.

  • Would it be possible to shield the mag from the interference.  I'm assume the interference from 600-700 size motors is quite powerful?

  • Well, I've purchased a hot air solder rework station so I will eventually be removing the compass on a spare APM 2.0 to experiment on as I got it cheap after someone cut traces to the GPS (before we knew about the solder bridge). I've got it fully functional right now so I will practice hot air work on some old dead pcb's befor attempting it on the APM...

    What I would like to see is just a new daughter board with only the data flash and two connectors for external Mag and GPS.

    Or, put the data flash on the main board and... wait, that's the 2.5 ;-)
  • I'd like to put an external magnetometer on a board HMC5883L at least 6" above the battery and power distribution with an APM 2 similar to what NAZA looks like. I already got the the uBlox Lea6 working with onbaord GPS disabled. I'm using it on a 3DR Hexa with 880 motors and 4S 8000mAh battery and can't get compass solid. How would I disable the onboard magnetometer and how would I connect the external board to the APM 2? Maybe someone can ponit me in the right direction. Thanks!


    Brad

  • Developer

    @Jeff,

         Yes, this is indeed an issue and needs to be sorted out for the trad heli.  I think 3dr may come up with an option to allow you to separate the compass from the main board.  Ahead of that..if it were me, I'd buy the unassembled APM2 and try to remotely connect the daughterboard with a long-ish cable.  It's a bit of a challenge with those really small pins though.

         BTW, on my most recent heli I used an APM with no daughter board at all and then it's quite straightford to connect an external GPS and compass.  the only issue then is you give up on having a dataflash..that was the sacrifice I chose..

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