Fly w/o compass calibration?

[Lionfish]

In my experience everything must align before a takeoff is attempted.
There isn’t any viable shortcuts that I know off.
Taking off with it be drone , heli , airplane is one of the most critical maneuvers the aircraft executes.
So in other words dot the i’s and cross all the t’s before attempting to leave the ground .
A preflight checklist is a good tool and I believe a necessary step with the CAA, the FAA and my favourite Transport Canada .
Usually if you think it through and it don’t make sense , well you know !!.
This hobby envelopes a lot of serious rules , regulations and lots of reading ,
But when everything works and your drone if flying high it’s a completely awesome feeling and totally worth the work.

So I’m sure you will get there and enjoy every minute of it .

 

[NLOL]

1) It appears on my ma2 that, on the map, a straight red line is shown, connecting the home point to the drone. Almost certainly this is GPS based. I find it handy if I happen to lose sight of the drone against a non contrasting background.

2) perhaps more relevant - I dont fly my drone blindfolded. I always keep an eye on it, and control flight visually. I see no need/use of a compas if GPS or my eyes are working.

So, like the op, I don't have a good understanding of the problems I'd have with a nonworking compass.

 

[Tentoes]

Often when it asks for compass calibration, all you need to do is move away from what's bothering it, like rebar in the concrete you're on. Asphalt usually does not have rebar. Neither does grass.

 

[Meta4]

I see no need/use of a compas if GPS or my eyes are working.

I don't have a good understanding of the problems I'd have with a nonworking compass.

Here's an explanation of what problems you can get into whit compass issues.

Compass issues show up if you try to launch with steel objects close enough to cause deflection of the compass.
If the steel item is big enough or if it is small and close enough to the compass, you get a compass error (better thought of as a compass warning) because the compass sensor detects a magnetic field of greater strength than the earth's normal magnetic field.
The drone won't allow launching and the situation is fixed by moving away from the source of the problem.

But a more serious potential compass issue is a yaw error which happens when the strength of the magnetic field is similar to the earth's magnetic field but the direction is different.
Because the strength is similar, it doesn't set off a compass error to warn you.

The gyros in the IMU are initialised based on the incorrect compass reading.
After you launch and exit the magnetic field, if you turn the gryos disagree with the compass and you get your compass error.
That's followed by the drone dropping GPS and falling into atti mode and depending on the difference between the false compass reading and actual, the drone may zip away in an uncontrollable curved flight at high speed in the worst cases.
The drone detects that it is off course and is attempting to correct but each correction puts it further off course.
Within seconds, it is flying at crazy speed.

Don't launch from steel or reinforced concrete surfaces.
It's asking for trouble.

 

[boblui]

... I dont fly my drone blindfolded. I always keep an eye on it, and control flight visually. I see no need/use of a compas if GPS or my eyes are working.

This is true only if you fly in ATTI mode in which neither the GPS nor the compass is used. But then the drone will be drifting around especially when there is wind. Moreover, you will not be able to use any of the intelligent flight modes, the craft will not be able to RTH in case of disconnection or low battery, long-exposure photos will be blur, etc, etc.

In short, no one will fly in ATTI mode except for special circumstances such as flying indoor.

I don't have a good understanding of the problems I'd have with a nonworking compass.

Imagine this :

- the drone is at position A and because of the wind it has drifted to position B
- B is to the south of A
- the drone decided that it should move north to get back to A
- If the compass is off by 180 degrees , the drone will actually be moving south without realizing it.
- as the result, the drone will be moving further and further away from A
- seeing the position error increasing, the drone will accelerate to correct the error more quickly.
- a vicious cycle will then be developed making the drone fly straight away . This was how my Mini crashed in the video in post #20 of this thread.

 

[WithTheBirds]

In short, no one will fly in ATTI mode except for special circumstances such as flying indoor.

You seem to ignore (or perhaps have no knowledge of, or experience with) the benefits that might be realised in acquiring smooth video takes in ATTI. The natural drift and loose response can work in your favour.

 

[boblui]

You seem to ignore (or perhaps have no knowledge of, or experience with) the benefits that might be realised in acquiring smooth video takes in ATTI. The natural drift and loose response can work in your favour.

I have flown in ATTI mode a lot with my DIY drones and all I have experienced is the unpredictability of the motion of the drone and busy stick inputs to keep the drone in the desired track. If you want smooth motion, use the cinematic mode

 

[Meta4]

I have flown in ATTI mode a lot with my DIY drones and all I have experienced is the unpredictability of the motion of the drone and busy stick inputs to keep the drone in the desired track. If you want smooth motion, use the cinematic mode

I use atti when the wind is favourable to help me to fly faster.

 

[WithTheBirds]

I have flown in ATTI mode a lot with my DIY drones and all I have experienced is the unpredictability of the motion of the drone and busy stick inputs to keep the drone in the desired track. If you want smooth motion, use the cinematic mode

I guess that’s an option. Doubt it’s better, for me anyway. With the exception of waypoints the intelligent modes can, with a little practice, be performed through manual control with greater control. Take an orbit for example. Even a small change in subject distance and/or elevation during the move can add a lot to the effect and it really isn’t hard to keep the subject in the frame. For me the automation is boring.

 

[PhantomFandom]

1) It appears on my ma2 that, on the map, a straight red line is shown, connecting the home point to the drone. Almost certainly this is GPS based. I find it handy if I happen to lose sight of the drone against a non contrasting background.

2) perhaps more relevant - I dont fly my drone blindfolded. I always keep an eye on it, and control flight visually. I see no need/use of a compas if GPS or my eyes are working.

So, like the op, I don't have a good understanding of the problems I'd have with a nonworking compass.

You're not understanding the intricate workings of the various navigation components that allow a quadcopter to hover and navigate successfully. It doesn't matter one bit that you see the straight red line or that that you have direct line of sight. The issue is that you may not be able to control the drone at all because under certain circumstances the drone will not be able to fly where you want it to.

If you were flying a fixed wing UA then your controls on the remote would directly affect the applicable control surfaces on the airplane (ailerons, rudder, horizontal stabilizer, etc...). This means that the aircraft is completely under your control and there is no need for accelerometer, gyroscope, compass, or GPS.

It doesn't work the same way on a quadcopter. You do not directly the control the the four motors, which are not only the propulsion source but also the source of directional control and stability. Instead the flight controller takes the inputs from the onboard instruments (IMU components and GPS) in order to come up with the proper power level for each motor (through the ESC). This is necessary for any phase of flight including launch, landing, any mid-air course direction change, and even hover.

So if you have the situation described above by @Meta4 , the FC will not be able to properly steer the drone or even maintain its current position. So it does not matter that you want the drone to go left or right. The drone literally won't be able to properly make that happen. As stated above, as the drone tries to correct the situation it actually continues to get worse and can lead to a fly-away.

So as to your original question, the compass is of VITAL IMPORTANCE. You cannot navigate your way out of that situation manually.

 

[NLOL]

It seems the compass plays a bigger role relative to the GPS than I expected, and I dont understand why a compass error should be the cause of turning off the gps. Lots to learn. Where can I find a technical article on how all this works?

 

[NLOL]

PF - thanks - that's an explanation I can understand ... makes me nervous though. I've found an area with greatly disturbed compass readings - GPS works fine. I suspect an undiscovered mineral deposit, and want to use the drone to help me explore the remorte and rugged area. Your post causes me to think I should only do that in ATTI mode, and makes me wonder if the AC Recovery features have any value in such areas?

 

[Lionfish]

Google , YouTube , the forum search option.

I would start there !

 

[Meta4]

makes me nervous though. I've found an area with greatly disturbed compass readings - GPS works fine.
I suspect an undiscovered mineral deposit, and want to use the drone to help me explore the remote and rugged area.
Your post causes me to think I should only do that in ATTI mode, and makes me wonder if the AC Recovery features have any value in such areas?

What makes you think that the area makes for greatly disturbed compass readings?
Unless you try to launch from on top of a boulder of haematite (63% iron), mineralisation in the ground shouldn't have any effect on a drone flying over it.
Flying this close to this much steel won't upset your compass:

RTH should work perfectly at normal heights even if flying over a mountain of iron ore.

 

[Tentoes]

But trying to fly through a steel truss bridge will!

 

[itsneedtokno]

Where can I find a technical article on how all this works?

A short explanation of compass function, calibration and errors.

BACKGROUND The aircraft compass is often misunderstood, both in terms of function and purpose, but it is important to understand what the compass measures, why, and what happens to that information. At the most basic level the purpose of the compass is to measure the earth’s magnetic field in...

mavicpilots.com

 

[WithTheBirds]

But trying to fly through a steel truss bridge will!

The best you can say is it might.

I regularly launch from reinforced concrete and steel structures and have no issues simply holding the Mavic above shoulder height when powering up and hand launching. The required separation from the bridge is probably significantly less than have assumed. Also, to the extent the bridge influenced the compass flying through the effect would be brief and immediately resolve when you cleared the structure.