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Here's something you should know about the 120m height limit
5283 14 2015-4-17
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woodielb
lvl.2
Flight distance : 78061552 ft
United States
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I must be the luckiest I1 owner around! First off, the update to the latest firmware was quick, smooth, and worked perfectly.
2nd, and the biggest, is that I crashed my bird about an hour ago due to some peculiar behavior programmed into the firmware. BUT, unbelievably, it survived with apparently no damage, just broken props.

Here's what happened. I was flying in the foothills of the mountains, going up and foward, maintaining clearance over the scrub oak, etc. I was just going to go through a battery to make sure everything continued to go smoothly after the upgrade. Had a short flight yesterday & everything was perfect. Maybe placebo, but I think the video looked even better. But today I wasn't even recording, though I had the gimbal on so I could see on my Iphone.

I had knowingly left the 120m height limit in the app turned on. As I approached 400' above me, at launch point, but only about 40' above terrain and about 10' or so above the top of the scrub oak, I got a warning on the app that maximum altitude had been reached. THEN, as I looked back up, the bird started descending vertically. At this time it's 400' vertical feet above me, about 675' away, but only 10' or so above the scrub. Despite full stick up, it continued to descend until it hit the top of the scrub oak. I heard the sickening weedeater sound of props on greenery, and saw it tumble to the ground. SH*T!!!!!  

Hiked up & retrieved it, found all the props broken (new quicklocks), with one off. It was laying upside down with the landing gear still up. The battery had released and slid out a couple inches, &  couple of the shock absorbers had released on the gimbal plate. I was sure I was going to find multiple broken parts, already going over getting the RMA, sending it off, etc. Hiked back down, got it home & checked it over. Took off the broken props, pushed the batterey back down, started the remote & then the I1, holding it by the back over a table. Lo & behold, the landing gear went down.

Went over it with a fine tooth comb, vacuumed & dusted, strong flashlight, nothing. Not a scratch. Not even on the top cover where it was laying. Put the same battery back in, turned on the remote, then the bird, everything normal. No cracks in the arms, etc. Though one does seem to have a bit more slop than the other. Ran it without props for about 5-10 min, listening to the motors, looking with a flashlight. Since that was my only set of QR props, took off the adapters & put a set of the originals back on w/proplocks. Took it back outside with the same battery (now at 84%) and did an IMU & compass calibration. Everything in the app perfectly normal. With much trepidation, (and recording video) took off and flew back up to 400' (but with more terrain clearance)  Got the same message, and the same behavior, a vertical descent of 10-20' that was not stoppable with input. Once it got back into what I guess it considered a safe cushion from max height, flew perfectly normally. Just checked video, it's fine.

There's not a scratch on it. When it descended into the top of the scrub oak, it must have kind of fell down through the boughs and plopped gently to the ground upside down. The gimbal & camera are untouched. One motor has some tiny nicks you have to look with a flashlight to see. Unbelievable!!

SO, keep in mind that when it hits the max height limit, it will descend to stay under it, in this case to about 390'. If you are, like I was, above launch by 400', but only a few feet above trees or terrain, it will crash and you can't stop it. At least I couldn't, but got amazingly lucky that the only damage was broken props.


2015-4-17
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jhannon66
lvl.3
Flight distance : 9013415 ft
United States
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Glad your outcome was good!

Sometimes when I'm ascending while going forward and stop ascending while continuing forward motion it appears do be descending even though it's just holding a constant altitude and continuing forward motion.  This is is mostly due to the vantage point.  Not saying that was the case here but you may be able to tell by looking at the the flight record in the app.
2015-4-17
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Farnk666
Second Officer
Flight distance : 1711394 ft
Australia
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Good to hear the damage was minimal mate - those damned trees!
The margin between the a/c's max height and terrain is all important and something we all need to keep in mind!
Thanks for the post and your story, I think there's something there for every UAV pilot to be thinking about and adding to the pre-flight plan.
2015-4-17
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Dangair
lvl.4
Canada
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I'm not at all happy with the ( max height ) thing. I live in the mountains and would like to terrain fly up into the creek draws, but the max height really limits the ground I can cover, heck the trees are 150' to start with. Throw a slope into that and I find myself being forced to turn around.
2015-4-17
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fullyestablishe
lvl.2
United States
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If you know that you need to climb to more than 120m but will remain way below that above ground level, then why not just turn off the 120m max then you are cleared to 500m. I climbed to 450m and was only 10m agl.
2015-4-17
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Bob Marley
lvl.4
United States
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Dangair Posted at 2015-4-18 12:23
I'm not at all happy with the ( max height ) thing. I live in the mountains and would like to terrai ...

I'm NOT either !!!

So what the heck if you are flying above trees, hills, mountains, in GPS at 400m ..... And then it drops out of GPS into atti ???

Does it descend down to 120m from 400m, with no way to stop it? (that would be a MAJOR problem).
So is that what you guys guess will happen?

Bob
2015-4-17
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Dangair
lvl.4
Canada
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Bob Marley Posted at 2015-4-18 12:59
I'm NOT either !!!

So what the heck if you are flying above trees, hills, mountains, in GPS at 40 ...

Bob, my issue, assuming you want to hear it, is that the terrain here is rather abrupt, our airstrip is a one shot deal. If you want to land a Cessna or even a piper super cub on our runway you must get it first time, there is no bail out. You fly over the lake and onto the strip, if you overshoot your done for. The inspire seems to be very limited in abrupt terrain because if you fly toward the hills you will quickly run out of room, even though you can maintain visual contact. In fact, lateral flying can be a tad limited in spots too because the trees are tall and tightly packed, this means loss of visual even at short range. So I have to be selective where I fly to really utilize the aircraft. The runway is good but it gets a bit boring after a few batteries.
2015-4-17
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woodielb
lvl.2
Flight distance : 78061552 ft
United States
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The big surprise to me was rather than just not climbing past 120 m it actually started to descend. Once it started I couldn't stop it. I repeated the behavior after checking it out post crash. Same thing, climb to 400', get the warning, & it will descend 10-20'. I guess I'll set my max to 500m, but I'll always keep in mind what happens when you bump the limit.
2015-4-17
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Tahoe_Ed
Second Officer
Flight distance : 2605 ft
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United States
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fullyestablishe Posted at 2015-4-18 12:34
If you know that you need to climb to more than 120m but will remain way below that above ground lev ...

You understand, the max height is 500m.  He had it set to 120m.  The 400' maximum will only be firmware imposed when you loose GPS and it is flying in ATTI.  
2015-4-19
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woodielb
lvl.2
Flight distance : 78061552 ft
United States
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Tahoe_Ed Posted at 2015-4-20 01:15
You understand, the max height is 500m.  He had it set to 120m.  The 400' maximum will only be fir ...

Thanks for the reply Ed, yes, the max was set at 120m & I was aware of it. I was just surprised when it automatically descended without the ability to stop it. I confirmed the same reaction on the subsequent flight. I now have it set to 500m, just wanted to relay the experience & give a heads up that the I1 will descend automatically when you reach the height limit, rather than just refusing to climb higher. I'm assuming it would do the same in the unlikely event you reached the 500m limit.
2015-4-19
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woodielb
lvl.2
Flight distance : 78061552 ft
United States
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BUT, to follow up on Bob's question, if you were above 120m & dropped GPS into ATTI mode, will it automatically descend to 120m? That could be a big problem.
2015-4-19
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RichJ53
First Officer
Flight distance : 1837356 ft
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United States
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Tahoe_Ed Posted at 2015-4-20 01:15
You understand, the max height is 500m.  He had it set to 120m.  The 400' maximum will only be fir ...

Tahoe_Ed

So, I have set my limit to 500M and do not have the limit slider turned on. So won't this let me fly to the 500M limit if I lose GPS? And in addition, won't this let me fly without limits if I am flying with GPS?
I understand the voluntary guidelines in the US, but there could be occasions that we need to turn off Big Brother.
Rich
Thank you for your clarification
2015-4-19
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Bob Marley
lvl.4
United States
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Tahoe_Ed Posted at 2015-4-20 01:15
You understand, the max height is 500m.  He had it set to 120m.  The 400' maximum will only be fir ...

BUT, to follow up on Bob's question, if you were above 120m & dropped GPS into ATTI mode, will it automatically descend to 120m? That could be a big problem
2015-4-19
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baron.oishi.gma
lvl.3
Flight distance : 2456043 ft
Canada
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I guess this will be easy enough to confirm ...
2015-4-19
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bornish
lvl.3
Flight distance : 91447 ft
United Arab Emirates
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Will try to help DJI bring full transparency on this subject by converting it to a formula definition.
Lets denote with:
- R the height as measured by the GPS receiver in the RC
- D the height as measured by the GPS receiver in the mobile device
- A the height as measured by the GPS receiver in the aircraft (I1)
- B the altitude as measured by the barometric sensor
- O the distance to below object measured by the sonar (part of OPTI sensor) available at the bottom of the aircraft (I1)
- M the terrain height in ref to Mean Sea Level (MSL) altitude
- E the terrain height in ref to WGS84 Ellipsoid
- X the maximum allowed height as defined in the DJI Pilot application
Based on the following scenarios, we should know the formulas (using above notations) which constrain the altitude of our aircraft, thus causing it automatically descend until the constrain is satisfied:
1. RC switch in P mode with GPS signal available
2. RC switch in P mode with OPTI (due to lack of GPS signal)
3. RC switch in P mode with no GPS (due to lack of GPS signal) or OPTI (due to higher than max range of the sensor)
4. RC switch in A mode (ATTI) flying manual but having GPS signal
5. RC switch in A mode (ATTI) flying manual without GPS signal available
Last thing to be explained is how are these constraints changing when the above scenarios are changing, meaning that the GPS signal is or not available, or RC switch is changed during flight from P mode to A mode!
Would be great if someone from DJI can clarify what is being used to constrain the height of our $3K+ aircraft while in mid-flight.
Please remember that we can only be as responsible pilots as our knowledge allows us to be.
Regards,
Bogdan
2015-4-20
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