Does RTH work with Compass Error?

[ianwood]

You know some folks said we couldn't fly to the moon. Some swear it was faked rather than admit they were wrong.

They couldn't do it with a Phantom. That's all I'm saying.

 

[syotr]

Of course. There is no air.
Amazing that they did get Apollo 13 home without GPS or compass. They did make some course corrections on the way. How about that Mars rover? No GPS there. Does Mars have a magnetic field?

As discussed earlier, we can get a good guess of the wind by drifting and a good rough estimate of the heading by flying forward. Combining the vectors, we should have a pretty accurate heading. So how close does it have to be to hold position and fly in GPS mode?
Here is a quick test I did to see how much error it would tolerate. Sorry the camera lost sight of the quad as I flew up and over the trees. It is mounted on my cap and I can't see exactly where it is pointed.
This quad has a NAZA controller, DJI ESC's and motors and an external GPS module with the compass built in.

And for the record, that was way more than 10 degrees.

 

[ianwood]

Compass is still contributing a fixed reference even if it's off by a bit. And as you may recall, the NAZA has a built in adaption for declination correction which would mitigate any effect from rotating the compass.

Now, if you let the compass loose and let it flop around in the wind, you'll see very quickly how important it is.

 

[syotr]

Compass is still contributing a fixed reference even if it's off by a bit. And as you may recall, the NAZA has a built in adaption for declination correction which would mitigate any effect from rotating the compass.

Now, if you let the compass loose and let it flop around in the wind, you'll see very quickly how important it is.

But what this shows is that the system could be able to tolerate some error in the heading if it were programmed to ignore the compass and use GPS and movement to derive a heading.
How does adaptation for declination work? I moved the compass and flew without recalibrating and did not wait for fast blinking led to indicate new compass lock and home lock.

 

[ianwood]

A rotated compass is still providing an absolute reference in three axes even if it is slightly off in two of them. So it's still providing a lot of useful data.

The NAZA compass adaption figures out the angle of error between GPS and compass and slowly applies it to the compass heading as it gains more samples. A2 does it too. If you live in a high declination area, you'll see the compass hook for the first minute of flight after calibration and then it's pretty much gone. The more you move on different headings, the faster it cleans up.

 

[George Weaver]

Just changed the shell and put everything back together (not many extra parts left over!).
Test flight I get the Compass Error - Exit GPS mode. Calibrated IMU's and compass prior to flight in the same location I always do. Did I screw something up in the rebuild? What would a bad compass connection warning look like?
P3P with all latest upgrades, no 3rd party apps.

Thanks!

 

[curiosity]

I would highly suggest the skeptics in this thread to watch the show, "MEGASTRUCTURES: ECOARK" that was aired on National Geographic, where a few young designers are trying to convince some experienced architects along the way, to prove them that their solution of constructing a building by using recycled plastic bottles would be feasible.

The young team is often blamed and challenged to be lunatic by the experienced, senior and elderly architects. However after months of hard work and passing all the tests, in the end, the seniors finally admit they were wrong, and those who believed in their project was absolutely right.

This kind of stuff always happens throughout the history. People are usually challenged to be lunatic for proposing what is believed to be impossible and are recognised as a genius once they are able to prove it working. And for this case, I don't think that it's even this hard to implement or that it could make its way to a documentary in NGC .

National Geographic Documentary - Megastructures - The Greenest Building in the Asia: EcoArk

A quote directly from the show at 39:20;

The junior designers are gradually gaining the approval of their elders. The EcoArk, has even won over construction engineer Linkou; “At the very beginning, I just felt a bunch of crazy people were trying to do something unachievable. Look at what we have finished! Now I think those crazy people were grouped up geniuses.”​

So feel free to call me a lunatic, optimistic, visionary, dreamer or even crazy. Looking at the type of people that has gained those titles once in their lifetimes in the past; I think I should be proud of it. And I'm leaving this discussion because it has started to take too much of my time and I simply don't have the time nor the motivation to prove this to those that don't believe it would be possible. I believe that some other dreamer will eventually make a compass-less RTH for commercial drones nevertheless.

Note: To prevent a misunderstanding -although it has been already said-, I feel obliged to state that I am not implying that this would be possible with the IMUs used in DJI's drones or that DJI would implement this in any way. I'm just telling that the idea of returning to a previously set home point without a compass is certainly possible. I totally agree with everything @syotr, @MikeyOnline and @Shammyh kindly shared so far - those have been some great reads, so thank you all!

 

[Mark The Droner]

Let's not forget the OP. Note that it's written in present tense.

 

[syotr]

Note: To prevent a misunderstanding -although it has been already said-, I feel obliged to state that I am not implying that this would be possible with the IMUs used in DJI's drones or that DJI would implement this in any way.

It was not possible to fix the "j hook" and "toilet bowl effect" in the NAZA Lite. until some hacker figured out how to load the NAZA M V2 firmware into it. The flight controllers have basically the same hardware.
It was not possible to fix the flyaways with the P1 and P2 which were always blamed on pilot error. Then the P3 was released and the problem seems to have disappeared. Could the changes that fixed the P3 be added to the P2 and P1? Who knows. Maybe there are hardware differences. No manufacturer wants to spend time and money on older products when adding these fixes would rob sales of the newer ones.
As for flying home without a compass, I believe the needed sensors and data is already available to the flight controller. The system already switches to Atti mode when compass is lost, so it is already drifting. GPS positional data is still being recorded as evidenced in the log file. All that is needed is a trivial calculation to get a close estimate of wind speed and heading. The system is already able to fly home in the wind. The only real change is that the heading is calculated rather than read from the compass. As demonstrated, the value does not have to be extremely accurate to fly.
I certainly don't expect DJI to do this on the existing models (although I do believe it is possible) but we could see something like this on later models. If another manufacturer does it first, DJI would soon follow.

 

[MarkEt]

So the $20 MEMS gyro in our flying toys should have the precision of three space grade mechanical gyroscopes that probably weigh 20lbs each and go into a billion dollar rocket?
.

Any $35 raspberry Pi kicks the *** of the computer once in Appolo. Big, biiiiiig time.

So, I wouldn't be surprised if our $20 gyros were in the same league as Appolo's.




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[MedinaTaylor]

Any $35 raspberry Pi kicks the *** of the computer once in Appolo. Big, biiiiiig time.

So, I wouldn't be surprised if our $20 gyros were in the same league as Appolo's.




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Actually the computer on my toaster is more powerful than that of the ones used in the Apollo missions.

 

[ianwood]

Any $35 raspberry Pi kicks the *** of the computer once in Appolo. Big, biiiiiig time.

So, I wouldn't be surprised if our $20 gyros were in the same league as Appolo's.

You would be wrong.

And, as good as they were, they had to be aligned to fixed reference points.