Meta4
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It depends on how much the compass data and GPS data conflict.
You may get a compass error message or your Phantom may swap to atti mode.
Both are shown here:
Does RTH work with Compass Error?
- Thread starter Mimoid
- Start date
You may get a compass error message or your Phantom may swap to atti mode.
Both are shown here:
Great video. Of course it's best not to do a bad calibration, but you often don't know it's bad until you are flying. I have seen lots of things blamed for calibration problems from rebar to magnetic rocks to distant power lines. I only recalibrate if I am going to be 100 miles or more from home. I use a magnetometer app on my phone to check the launch area before calibration or takeoff.
What is disturbing is that there have been many flyaways after successful flights in the same area. Something causes a compass error in flight. I have had this happen.
Precisely. Plus... you never know what idea might give birth to other ideas...
If folks haven't seen this TED talk, it's worth a watch, it's specifically about drones: Raffaello D'Andrea: Meet the dazzling flying machines of the future | TED Talk | TED.com
In particular, the final demo is rather amazing.
~~~
As to the thread topic: Will a P3/P4 enter into RTH in event of compass failure? No. Answered.
Will we ever see a P3/P4 update that allows for RTH in event of compass failure? Almost certainly, no.
Is it *possible* to RTH without the compass? Almost certainly, yes.
~~~
Life is about more than "deliverables". No-compass RTH is a fun and interesting engineering challenge to consider.
And who knows... maybe someone on this very forum is an undergrad/grad student at university, and is working in some field of engineering.
Maybe they see this thread, and say "hey, I wonder how I could make compass-less RTH work in a quad?". And the rest is future-history.
Taking a look at an impossible problem and saying "but wait, what if we tried X" is a fundamental requisite for human advancement.
Imagine the first humans/proto-humans to harness fire. Imagine the first scientists to sit down and brain-storm the logistics of the Apollo program.
Heck, look at Advanced-LIGO. It is making the most precise measurements in human history, so precise, it recorded a vibration in space-time from black holes colliding 1.3 billion light-years away.
Einstein, the very man who came up with the theory LIGO is testing, thought gravitational waves would never be measured by humans.
Not a lot of people win by starting with "but I think Einstein wasn't quite visionary enough".
Yet some scientists, thought, hey, let's spend a billion dollars creating an instrument that may in fact never measure anything. But they did. And it worked.
We need both of course, the pragmatics and the dreamers.
The dreamers take impossible problems and create impossible solutions.
The pragmatics take impossible solutions and turn them into realized solutions.
One might even argue these are two sides of the same coin.
Anyway, that's my OT rant for this thread. Shammyh out.
Wow! It was such a nice read! Thanks for this great contribution Shammyh!
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The Phantom GPS knows where it is. It know the GPS coordinates of home. I don't understand why it has to point at home in order to go there. We can fly our phantoms frontwards backwards sideways various angles using the joysticks. I don't understand why the GPS can't just drag the phantom at any angle back to the home point.
I really hope someone could help me understand why this can't be done. I know DJI hasn't done it but is it possible if they want to?
I really hope someone could help me understand why this can't be done. I know DJI hasn't done it but is it possible if they want to?
Space ships rely only on gyroscopes to keep their heading and if this were not reliable then we would seldom see astronauts back on earth ;-)
Don't reply with stuff like absence of wind in space. Missing the point.
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It does not need to point at home to fly back, but it does need to know which way it is pointing, otherwise it would not know which motors to engage to head towards home. As discussed earlier, it can determine its orientation and then fly as you described.
ianwood
Taco Wrangler
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?
Not to mention that mechanical gyros are totally different to MEMS gyros and that they would both behave differently in zero g.
Let me clarify overall: this is not achievable with enough accuracy given the existing grade of equipment in the P3. Put in an array of high quality IMUs and high frequency Madgwick sensor fusion algorithms on an FPGA, you could pull it off.
But... But... I thought my Phantom was as advanced as a $30 million ballistic missile! You're telling me it's not?!
To be fair, still pretty impressive how accurate the P3 IMU is... But no, it definitely can't do full "inertial navigation" like a missile/rocket/space-ship can.
And yea, effect of gravity is different in space. Technically, it's not zero G, since, well, there is no such thing as "zero gravity", anywhere in the Universe. But yea, they actually do make very high precision MEMS gyros, and they are in fact replacing more traditional mechanical gyros for space applications, but the precision of our P3 gyros is no where close.
Either way, as I think we fully covered earlier in the thread, the P3/P4 gyro is not sensitive enough to be used for inertial navigation alone.
I don't think you need that level of precision. The gyro in my $100 toy quad that has no GPS or compass manages to hold yaw steady for quite a while, even in windy conditions, all while tilting and flying around. The gyro doesn't have to maintain perfect angle the whole flight. If it can hold the yaw within 5-10 degrees for a minute or so, that's long enough to run the "find home" algorithm in order to keep adjusting continuously.
Mike
Mine is going right back to Micro Center this afternoon!But... But... I thought my Phantom was as advanced as a $30 million ballistic missile! You're telling me it's not?!
ianwood
Taco Wrangler
But it's not navigating. A 5 degree error can result in a big difference over a couple hundred feet. Add another 5 degrees over the next couple of hundred feet and you could be off by a large distance. And that low an error is still wildly optimistic given what wind will do.
And you still have to figure out which way to go in the first place. You'll get plenty of IMU drift just trying to determine which way is home.
All current models with nav have a compass and most older models did too. My 2006 S4 had a compass that was used by the nav.
By the time you've flown a couple hundred feet, you've been through the adjustment algorithm many times, making minor adjustments. If it's ability to hold yaw was that bad, you wouldn't be able to fly it in Atti mode. It'd be all over the place. The fact that you can fly it home in Atti mode after losing the compass means the AC can do it too. When you get a compass error and it ignores the compass and puts you in Atti mode, you're doing the same thing the "find home" algorithm would do: start flying it, watch which direction it's going, and start moving the sticks until it is heading in the right direction. If the IMU is as bad as you suggest, you'd never be able to bring it home either.
Mike
ianwood
Taco Wrangler
No, it doesn't. You can see. Try flying ATTI with yours eyes closed. That would be similar. Turning off the compass is like walking around with a blindfold on. With a single consumer grade IMU and only limited sensor fusion capabilities in the Phantom, it is simply not possible with any degree of reliability. End of story.
If you understood AHRS navigation systems, you would know that common gyro MEMS drift like crazy and do not provide reliable headings. It's really that simple. A drone without a compass hovering steadily does not mean the IMU can predict a heading. They do not answer where you are pointing. They answer how fast you are turning. Not the same thing.
Nope, they don't. My wife's new Prius with nav has no compass. It's an option that goes on the mirror. My Dodge Challenger has no compass. Two of my handheld Garmin GPS units have no compass.
None of that matters. The AC has the same information you have when flying Atti: the direction you are going. And the AC knows it's course a lot more accurately than you do looking at a little dot in the sky. When you lose compass and you have LOS, you look at the AC and and press up on the right stick. You watch the dot in the sky and notice it's moving to your left, so you move the left stick to the left a little until there's no more side (left movement) and watch to see if it looks like it's getting closer (it should be with your thumb still forward on the right stick). The AC can do the same thing with nothing but GPS. And you're not going to be accurate to 3m watching it from a few hundred meters away, yet you can get it home. I know I have and I would think most here can. If you can get your orientation and direction just by a few maneuvers, surely software can do it with the exact same information.
Mike
It's possible they have a compass, they just don't display it on the mirror. My Dodge Challenger has a compass. I presume it's used for GPS because in the GPS screen, you can "calibrate" the compass by chosing your zone. On my Challenger, the direction shows up on the display but I suppose on some cars, they just don't show it (but the nav system might still use it).
Mike
Just like in your car, the GPS doesn't know your orientation until you start moving. We have all seen this. It only knows where you are. Now, it does know the home point location, similar to navigating in a car to a given location. All that is missing is either guidance, such as spoken or displayed prompts to get you to back to point A from point B.
The aircraft can see (much better than you.) It has GPS. It knows it's exact position all the time. It is not flying blind. Is that so difficult to understand?
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