Neither P4P will maintain altitude

[F3honda4me]

If there was anything at all I could give you to prove and assist you with what you're claiming is happening I would. I've helped many people like that. But in your case there is video plus 3 independent systems all telling the same story.

If you feel there is an issue no one but DJI can help you at this point then.

 

[F3honda4me]

I would be happy to try that, I'm just not sure you'll be able to see a drone accurately 200 feet away. I will give that a shot tomorrow. The second video obviously shows the descent but I was there, so I can understand it may not be as clear. You can still see the drone climb though after stopping and hovering. The second video shows clearly that the drone is in a descent. It then climbs back up to the height it once was. Honestly not sure how that's difficult to ascertain.

It does go down then up but not to the degree you are making it out to be. It's within normal variance. Your eyes at 200 feet away on an object that small can't see the difference between a 5 foot climb/descent and a 15 foot climb/descent. This is why we rely on the logs to verify or in this case disprove the suspected behavior.

 

[jpk1080]

I disagree. Someone can help me, but that person may not be you. Again, watch the second video. Watch it pass by the power poll and watch out low it is when it ends up at the fence. Then it mysteriously climbs, not with input, but to correct for the height it descending over the 300 feet or so it descended. The gps and vps are reading out huge variances in altitude.

 

[F3honda4me]

OK maybe that's the wrong term. What I'm saying, when I look at my footage it always looks like I'm closer to things than I really was.

Exactly. Including the ground.

 

[jpk1080]

Honda, I can not only see my drone is a few feet of the ground, I can verify it with the vps. When I fly down the street at my house, I start at approximately 10 feet. Its much more obvious that the drone is descending when you start at that height.

 

[F3honda4me]

I disagree. Someone can help me, but that person may not be you. Again, watch the second video. Watch it pass by the power poll and watch out low it is when it ends up at the fence. Then it mysteriously climbs, not with input, but to correct for the height it descending over the 300 feet or so it descended. The gps and vps are reading out huge variances in altitude.

Again normal. GPS height has a margin of error of about 16-20 feet. VPS becomes inaccurate during high attitude since the ultrasonic on the bottom of the craft change angle to the ground.

 

[jpk1080]

Honda, again you're making assumptions. When I was in Palm springs, I wasn't always moving in a direction away from me. I also flew the drone towards me, and in various directions including circles. The drone literally was slowly descending and continuing to until I stopped it.

 

[jpk1080]

Great. When my vps says I'm at 20 feet though and 200 feet later I'm 2, there is a problem.

 

[F3honda4me]

Honda, I can not only see my drone is a few feet of the ground, I can verify it with the vps. When I fly down the street at my house, I start at approximately 10 feet. Its much more obvious that the drone is descending when you start at that height.

I told you what the VPS says your height is the moment you let go of the sticks and the drone levels out. It's about 15 feet. Not a "few" feet. And this is before the climb.

And yes the drone will drop a few feet when you make a 30mph run. Totally normal. So when you start at 10 feet a few feet cuts your distance in half to the ground. Again totally normal. Every drone does this. My p4p does this. My inspire 2 even does this.

 

[F3honda4me]

Great. When my vps says I'm at 20 feet though and 200 feet later I'm 2, there is a problem.

At no point does your VPS ever go below 14 feet in the entire DAT during any of your runs.

 

[jpk1080]

I will post up more video tomorrow so you can hopefully see the issue. The vps on the dji go app literally says 2 feet. I'm not guessing here. I also get the audible warning that I'm close to an object.

 

[AlecW]

Exactly. Including the ground.

We are on the same page. I didn't notice any gradual decent other than what's normal at speed. I tend to fly slowly when close to the ground though.

 

[jpk1080]

Like I said, I will post up video tomorrow. What the vps is reading and what the dat file are reading are not in agreement then. What kind of drop is considered normal? I can try to capture an iphone video and do a spiral to show the descent. That way, I can hopefully put an end to the questioning.

 

[Rayven-Eye]

I have seen this issue before....here is the question, are you using the same remote controller? If so, it may be a mechanical issue with the controller.

 

[Meta4]

What in saying is those numbers are not correct. The gps and vps are way off from each other.

You should ignore any GPS elevation data - the Phantom does.
That's because GPS altitude is horribly inaccurate and varying over short time frames.
The Phantom only uses barometer for altitude data

 

[jpk1080]

Unfortunately it using different controllers for all drones. Thanks meta for the info. The vps height indicates a descent which is verified both with the app and visually. The app will show a descent of .4 to .7 mph. The vps will then indicate it is at a lower altitude and it will begin to climb once placed in a hover.

 

[D'sAdvanced]

Only one DAT contains a flight in this dropbox, and it was about 5 minutes long. Everything I can see looks totally normal. The first time you hit the elevator to travel forward, the drone climbed about 3 feet which is pretty normal for a full out 30mph sprint. The next 8 second sprint, this time in reverse, did the same thing. Later on, two 10 second sprints, one forward, one reverse, and the drone did the same, climbed a bit during the sprint.

I am not sure why you think the drone is dropping and going to crash into the ground?

AFTER your sprints, the drone drops back to about the height it was before the sprint started, which is normal also. At no point while sprinting forward or backwards is the drone losing height, but is actually gaining height a bit.

At low heights the drone may look like it's dropping but it really isn't. It's an optical illusion.

I circled the sprints:

Guys,
I'm experiencing the exact same issue with my P3A. I can attest that we are not lunatics - I've flown for a few years and have taken drones apart and put them back together. There is something going on here. The drone drops slowly when at full speed and would hit the ground.
I will experiment with it tomorrow.

 

[D'sAdvanced]

I disagree. Someone can help me, but that person may not be you. Again, watch the second video. Watch it pass by the power poll and watch out low it is when it ends up at the fence. Then it mysteriously climbs, not with input, but to correct for the height it descending over the 300 feet or so it descended. The gps and vps are reading out huge variances in altitude.

Correct, that's what mine does. Say I start at 20' altitude and run full speed for 75 yards. By this time, the drone is 5 feet off the ground. As it finishes braking, it will ascend to/or close to the original altitude. I will film it tomorrow. In any case, please don't dismiss the OPs statements as I am experiencing the same issues.

 

[spirytus]

You should ignore any GPS elevation data - the Phantom does.
That's because GPS altitude is horribly inaccurate and varying over short time frames.
The Phantom only uses barometer for altitude data

Good point but I'm not so sure the phantom is actually ignoring GPS elevation. Had a quick look at the data:

Right after he pitches full forward and the phantom begins its forward traverse, GPS altitude (erroneously) spikes up in altitude while his throttle remains neutral. Going by the assumption that the flight controller is not ignoring GPS data (P mode?), I'm thinking it's trying to compensate for the unwanted GPS elevation increase by attempting to descend.

Right after he stops, (and finally receives accurate GPS elevation data) you'll notice a sudden drop in elevation (lower than when he begun forward traverse, since he did infact loose altitude). So the FC corrects this discrepancy by commanding the motors to ascent until it reaches the user requested altitude.

The gradual descent during forward flight and the altitude correction after he stops is clear in the video.

When I have more time, I'll plot a graph for you guys.

P.S. If I wasn't working and the weather was better I'd test this out on my P4P but I'll probably experience the same flight dynamics as you -- I think honda is right in stating this is nominal behavior for DJI quads that relay heavily on sensor data - my experience with "assisted" flight here is limited since this is my first DJI product, all my other quads are fully manual. If you feel brave try it in ATTI mode (which should ignore GPS altitude data) and see if the gradual descent goes away - just be very careful. Flying low to the ground in ATTI mode is not for the inexperienced.

 

[BudWalker]

I also had a look. At the beginning of the run the AC gains altitude as it starts to increase speed. There is a descent, but it's not gradual; it's all at the end of the run where the AC slows down. After the run there is a gradual increase to get back to the proper altitude. Here is the first run out past the baseball diamond and the second run back to the home point.

The first run started at 244 where the speed started rising above 0. The AC had gained 1.5 meters in altitude by the end of the run and braking started. This is where the drop of 2.5 meters occurred. Finally, at 258 secs the AC had stopped, was hovering and the gradual ascent to home point altitude started. That gradual ascent was cut short by the beginning of the second run back to the home point.

My P3A, P3P, and Mavic do this. I've looked at a couple of P4P flights that I have data for and they do it as well. Doesn't matter if it's the .DAT file from the AC or the .txt from the App. In fact ,one of my flights used AutoPilot.

It's apparent from the videos that there is a gradual altitude increase after the run and the AC has stopped. But, to my eyes at least, an altitude change in the first part of the run isn't apparent. This means that, in my case at least, that I'm not able to see the drop while the AC is in motion. Without actually knowing the profile of that drop I would probably assume that it had to be gradual. I would also expect that if the AC were flying straight at me it would be very difficult to determine if the descent were gradual or occurred during the braking.

@jpk1080 can you try a different experiment? As before fly it out past the baseball diamond. Then wait until it has reached the home point altitude. Then, on the return run don't remove the elevator input until it's past you and observe it's altitude as it flies past. The AC should fly past you a little above the home point altitude. It will have gained a little altitude during the first of the run as the speed is increasing. If you post the results it doesn't matter if it's the .DAT of the .txt.