magnetometer testing inside house
« on: August 19, 2017, 11:54:28 am »
I find that it's quite hard to find a spot inside my house that's 'magneto-neutral' enough to get 'all green' on the flightdata page. GPS fix will take a while inside (2 - 20 minutes), but eventually it will go green (UBlox 7m). The magnetometer however ..... Well I found a quick fix; just put a magnet in the vincinity and move it about 'till you find a sweet spot. I keep it as far apart from the mag as possible, cause I don't know if a strong magnet can permanently damage the magnetometer if held too close, so just put it close enough to get <.5

Not suited for calibrating the mag (I think), but handy for testing when it's bad weather or when using a cable connection to the FC and you need the mag to be stable.

WARNING:  I AM using the Rev's internal magnetometer, but it's on a 450-and-a-little custom made frame and the mag is (elevated) 4" away from the nearest powersource and >10" from the motors. So if your flying a 250, DO NOT tape a magnet to an arm!!! Don't use some supermagnet (I use a whiteboard magnet) and start out from a firm distance and work your way in.

All at your own risk ofcourse. But it works for me.
If it ain't broke, don't fix it! But I can't seem to take my own advice ;)


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Re: magnetometer testing inside house
« Reply #1 on: August 19, 2017, 12:03:40 pm »
Adding a magnet to correct a already disturbed Mag is a strange way for "quick fix", in practice you do a earth's magnetic vector correction to match your current calibration.

In all cases not a durable solution for safe flying or calibration. :)

Re: magnetometer testing inside house
« Reply #2 on: August 19, 2017, 05:23:22 pm »
Mag calibration, health color, and correctness use both the direction of the mag field (for vehicle direction) and the strength of the mag field (to try to verify there is no disturbance in earth's field).

If you start with the mag being calibrated correctly and if you don't get the magnet too close to the vehicle, this might be useful, but the only reasonable use for this would be to get the mags green so you can arm where you would not normally be able to arm, like indoors, and only for non-flight, indoor testing, or later carrying it outdoors for flight.  In essence, you would be getting the mag field strength correct (so health is green, so you can arm), but not the direction.

To start in a location where there is a disturbance, and place a magnet to fix both direction and strength at once is basically impossible without some very fancy equipment.  Even with this, since the magnet you use is only detectable in a very short range, the area that is corrected by it will be very very small, so moving the vehicle or magnet even a short distance will undo the correction.  Just not reasonable except in a lab.  :(

Then there are AC magnetic fields because of AC wiring in the house.  The mag field changes constantly.  To see an example, hold a fan (like desktop fan) close to an old style (CRT) TV set or computer monitor.  Where I used to work, there was an area around a power panel (including high current air conditioning) where you couldn't use a CRT.

Re: magnetometer testing inside house
« Reply #3 on: August 21, 2017, 02:49:07 pm »
Ofcourse it's not for flying. Like I said, it's for testing on a rainy day inside the house, where there's magnetic disturbences ev'rywhere, so I can't get stab and atti to go green. Which I need for testing (arming). It's props off ofcourse!
If it ain't broke, don't fix it! But I can't seem to take my own advice ;)

Re: magnetometer testing inside house
« Reply #4 on: August 22, 2017, 02:26:05 am »
I can often get it to go green by moving it around and flipping it around.  :)