What are effects of bad compass data, really ?

My understanding is the compass calibration sets up North position for the GPS and
after its calibrated your good to go unless you take your quad miles away.. re-calibrate is recommended. Also want to be sure then you do the initial compass calibration that their are no metal interferences which would give you a bad calibration (setting North position) which could lead to quad traveling incorrect GPS coordinates. Any others have any insight on the compass calibration.
Interference front cell towers and other electronic interferences could cause you to lose communication between the RC and quad.

 

very interesting info. I have never had any idea how compass was used with the gps.

how did you come to this understanding please?

 

It comes from an understanding of copter control functions, I can point you to a site that explains it also. Do a google search on Quadcopter control functions. Interesting stuff. Http://Diydrones.com/forum/topics/Quadcopter-control-functions-layers then. read under orientation. Hope this helps
I.E.
Quadcopter starts to set orientation to face certain direction. It needs a sensor that gives different readings when it rotates horizontally. This feature is achieved by using magnetometer. Magnetometer is simply an electronic compass, it gives readings in X-Y-Z directions, but what we focus here is the Z-Axis assuming quadcopter is horizontal; some math is required to get the absolution magnetic field direction if quadcopter is not horizontal in case we look for high accuracy.
So in essence it tells the copter direction... North mainly.

 

The processor combines inputs from the compass, GPS, accelerometer and barometer to calculate position, orientation stability and direction.
Combining the sensors improves accuracy.
If one of these sensors gives a false reading then the phantom will miscalculate either position, orientation, stability or direction.

So no, unlike your car, it won't go into limp mode and get home safely if a sensor is wrong, it is likely to crash instead.

 

While all GPS receivers can tell where you are, entry-level models have no way of ascertaining which direction you are facing. So you have to start moving and walk a few steps at a good pace before it can accurately point you towards your destination. This is why mid-range and high-end units have an electronic compass — to show the direction you should travel even while standing still.
This can be found in any GPS operation information. Compass Needed !!!And so back to the Magnetic Compass.
GPS manufacturers recognise that whilst a differential compass is fine most of the time, users still like the security of a magnetic compass. The traditional magnetic compass has been fitted with electronic sensors and bundled into some of the GPS devices. This is what is meant when a GPS is advertised with an electronic compass. It costs a little more but allows you to take bearings when stationary or out of sight of the satellites.


Hope this helps


Roy