Ferrous Compromised Landing Site

[EricJT]

Quick question....I am familiar with not taking off from a ferrous compromised surface, but what about landing on a ferrous compromised surface?

 

[SkyeHigh]

Quick question....I am familiar with not taking off from a ferrous compromised surface, but what about landing on a ferrous compromised surface?

Not a good idea. The IMU is initialised with the compass heading prior to take-off, which is where any ferrous material causes the greatest issue. But you may get a cannot land prompt for a manual landing, an issue with RTH as it orients itself prior to landing or worse unpredictable movement when trying to land. I would at the minimum expect a magnetic interference prompt when close to landing.

Of course it all depends on how strong the magnetic field is.

Edit: To avoid confusion I should clarify, I mention ‘take-off’ being the logical follow-on from powering up prior to a flight. As Slup infers, subsequent take-offs do not reinitialise the IMU with compass headings unless the aircraft has been power cycled or battery changed.

 

[EricJT]

Not a good idea. The IMU is initialised with the compass heading prior to take-off, which is where any ferrous material causes the greatest issue. But you may get a cannot land prompt for a manual landing, an issue with RTH as it orients itself prior to landing or worse unpredictable movement when trying to land. I would at the minimum expect a magnetic interference prompt when close to landing.

Of course it all depends on how strong the magnetic field is.

Thx....I wasn't sure if the dones's compass would be affected even though it was properly initialized at takeoff. Better safe sorry.

 

[Meta4]

Thx....I wasn't sure if the dones's compass would be affected even though it was properly initialized at takeoff. Better safe sorry.

The compass doesn't get initialised.
It just responds to whatever magnetic fields are around it, whether that's just the earth's normal magnetic field or the field around any large iron or steel objects close by.

If you have a large steel roof available, you can try slowly lowering your drone towards it sometime.
As the drone gets closer, the magnetic field of the roof will become stronger than the earth's field and you'll see the drone start to wander in a swirling pattern.
Give it some throttle to climb away from the magnetic field and the drone regains directional stability.

 

[slup]

Magnetic interference mainly affect the drone when you power it on & a couple seconds after... as it's just there the IMU reads off the compass cardinal direction. After the IMU have been initialized it's the IMU that matters in the following take-off, flight, RTH & landing.

During flight various sensor outputs (mainly gyro & compass) sends slight corrections to the IMU regarding the heading but this is a slow process & usually nothing to consider if not hovering or flying in a stronger magnetic field for a longer time.

So the only obstacle to handle in order to avoid a yaw error due to magnetic interference... is to power on the drone without magnetic interference that deflects the compass.

A safe drill for this, is to power on the drone in your hand (without rings, bracelets & watches), then stretch out your arm with the drone in front of you so possible magnetic thing's in you clothes (belt buckles, buttons, zippers) are as far away as possible, in this way you have positioned the drone as far away from hidden magnetic interference ... once the live view have appeared in the app you can be certain that the IMU initialization have been finalized. Now you can put the drone some where on ground, let it aquire enough sats & get the HP recorded... then before you take off, always check the drone symbol on the app map & make sure it points equal in relation to map objects (like roads, houses) as the drone does in reality, if it's ok you can take off, if not, power down the drone move away & repeat the above process.

So... a wrongly initialized IMU due to a deflected compass have nothing to do with the "take off", it's only related to the powering on of the drone. Magnetic disturbance after the powering on with a successful IMU initialization rarely affect the drone if not in it for a rather long time, it's strong & very near the drone.

 

[DougMcC]

I regularly launch my M2P from a site on the street about 5 feet from a manhole cover and 8 feet or so from my parked JEEP. After booting the aircraft and after satellite acquisition I always pick up the bird and rotate through 180 degrees and check map coordination. I return to the same site at the conclusion of the flight. That “Chubby Checker” twist prior to launch is a key part of any preflight. A compass calibration is performed if the Twist fails.

 

[slup]

...That “Chubby Checker” twist prior to launch is a key part of any preflight. A compass calibration is performed if the Twist fails.

If that "Chubby Checker" twist with same time comparison of heading direction map & reality fails... ie. drone symbol doesn't point as reality relative objects, a compass calibration will not solve anything, especially not a yaw error... your drone will go haywire at height anyway.

The only thing that solve a yaw error is a re-initialization of the IMU by a compass that isn't deflected by magnetic interference... you do that by powering off the drone, move away from the interference & power on.

 

[DougMcC]

If that "Chubby Checker" twist with same time comparison of heading direction map & reality fails... ie. drone symbol doesn't point as reality relative objects, a compass calibration will not solve anything, especially not a yaw error... your drone will go haywire at height anyway.

The only thing that solve a yaw error is a re-initialization of the IMU by a compass that isn't deflected by magnetic interference... you do that by powering off the drone, move away from the interference & power on.

I agree, a failed twist alignment warrants a new site and a restart and perhaps a calibration if the GO4 software calls for it. Even then a twist confirmation should be repeated.

 

[slup]

...and perhaps a calibration if the GO4 software calls for it.

The only thing a compass calibration does is to measure the drones own internal mag field... this so it can be deducted from the total mag field the compass senses (which is drones+earth mag field).

So a calibration is only useful & motivated if you have put on or taken off equipment from the drone that might have changed the drones own mag field.

Now I know that certain firmware's have a compass calibration trigger coming from days since & distance from the last calibration... & those you can't get around. But all other calibration prompt's in the app should be questioned... they can instead originate from that the sensed mag field strengths is outside a threshold value coming from being in magnetic interference... & a calibration there will just make thing's worse. If a unexpected calibration prompt comes up in the app, power down & move away instead... just do it if it doesn't disappear after several location changes/power cycles.

 

[DougMcC]

The only thing a compass calibration does is to measure the drones own internal mag field... this so it can be deducted from the total mag field the compass senses (which is drones+earth mag field).

So a calibration is only useful & motivated if you have put on or taken off equipment from the drone that might have changed the drones own mag field.

Now I know that certain firmware's have a compass calibration trigger coming from days since & distance from the last calibration... & those you can't get around. But all other calibration prompt's in the app should be questioned... they can instead originate from that the sensed mag field strengths is outside a threshold value coming from being in magnetic interference... & a calibration there will just make thing's worse. If a unexpected calibration prompt comes up in the app, power down & move away instead... just do it if it doesn't disappear after several location changes/power cycles.

Thanks. It hasn’t happened often but I noticed as I traveled from Southern CA to northern CA whatever version of GO4 was present would often be triggered for a calibration.