MultiNav Pro+ sensors magnetometer - calibration routine needed or plug and play?

@Nicholas Felt yeah, your instincts are right to ask this — and honestly, given your background with HMC5883L and QMC5303, you already know the answer before I say it: no magnetometer ships with hard/soft iron cal that's specific to your installation environment, and that includes this one. Factory calibration on the IC level covers offset and sensitivity trimming on the chip itself, but hard iron distortion comes from the ferromagnetic materials *around* the sensor once it's mounted on your frame, and soft iron distortion from things like motor currents and ESC wiring. There's no way to pre-calibrate for that.

 

So yes, you'll want to run a calibration routine before you trust the heading output. A figure-8 or tumble cal sequence is exactly the right approach, same as you've done before. The good news is the module exposes raw magnetometer data so you can pull min/max values across all three axes and compute your hard iron offsets and soft iron correction matrix yourself, or feed it into whatever AHRS library you're running on your flight controller.

 

Worth noting — at low-speed GPS conditions where you're planning to lean on mag heading, motor interference is going to be your biggest enemy, so mounting distance from ESCs matters a lot. If you're on a fixed-wing or large hex where you can get the sensor 10+ cm from power wiring, you'll be in good shape after a solid cal. On a small quad it's trickier.

 

If you haven't already, jump into the Dev Hub resources section — there's AI firmware tooling there that can help you build out the calibration logic if you want to implement it onboard rather than handling it externally.

The MultiNav Pro+ does ship with a basic factory offset cal but honestly in my experience it's not enough if you care about accuracy - you'll definitely want to run your own hard iron calibration at minimum, especially since your drone's motor/ESC interference will swamp whatever they did at the factory. Do the figure-8 routine after final assembly with everything powered up, that's the only way to capture the real magnetic environment your sensor is actually sitting in.

Keith is 100% right on this - factory cal is basically just a starting point and motor noise will trash it anyway. One thing I'd add: if you're pulling heading from the magnetometer during flight, do your calibration spin *at the same altitude and orientation* you'll actually be flying, some people do it flat on a bench and then wonder why their readings drift when the drone tilts. Also worth logging raw mag vectors during a test hover before you commit to any fusion algorithm, gives you a good sense of how bad the interference actually is in your specific setup.

Both Keith and Revital nailed it - just want to throw in that soft iron cal is worth the extra effort too, not just hard iron, especially if you've got any steel hardware or carbon fiber near the sensor (CF can be surprisingly problematic). I used a simple ellipsoid fitting routine on my last build and it made a noticeable difference in heading stability during banked turns where the field vector angle changes relative to the sensor axes.

Agreed with everything above, and just to add one more wrinkle - if you're planning to fuse the mag with IMU data (which you probably are for a drone), make sure you redo the cal after you've finalized your sensor mounting and any vibration dampening, because even small physical changes to what's sitting near the magnetometer can shift your hard iron offsets enough to matter. I went through two cal sessions on my last build because I swapped out a motor mount between them and couldn't figure out why my heading was off by like 8 degrees. Annoying lesson but worth knowing upfront.

All good points here - one thing I'd add from my own builds is that if you're running a compass/IMU fusion stack like Mahony or Madgwick, the mag influence is usually weighted pretty low during dynamic flight anyway, so even a mediocre cal is often "good enough" for attitude, but for actual heading reference at low speed (your use case) you really do feel every bit of cal error. Worth spending the extra 20 minutes to get soft iron done right from the start rather than chasing drift issues later.