Return to Home collision question

Discussion in 'Mavic Pro Help' started by rob968, Nov 20, 2016.

  1. rob968

    rob968 Member

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    I got my Mavic a few days ago and have really been enjoying it. This is my first DJi drone, so I'm still acclimating myself to all of the controls and data on the screen. I've been taking it slow and flying in my back yard, which also has a very large, open agricultural field neighboring it for plenty of open flying. I was at the end of a flight yesterday and ran into some issues landing.

    The battery had about 17% remaining, and I was attempting to land on my back patio. I was taking my time, as I'm still new to this drone, I didn't want to make any stupid moves, and I thought I had plenty of battery left to make a safe and deliberate landing. So much for that plan. I originally took off from the side of my house, and that's where the return to home point was set. As I was coming down for a landing in back of the house, the automatic Return to Home function kicked in, and to drone headed to the side of the house. It was relatively close to the house at this point and hit the pause button, but it did not stop the bird. Again, I'm a rookie so my first reaction was probably the wrong one, and the bird kept moving forward.

    As it was heading to the RTH point, it hit the side of the house and crashed to the ground. It's obviously pilot error in regard to improperly anticipating auto return to home, or resetting the RTH point, but that's part of the learning experience and a separate issue.

    My question is why the obstacle avoidance sensors didn't prevent collision with the house. It ran straight into a pretty broad area without any activation of the sensors. It's like the feature was deactivated. Before the flight, I went into the menus to ensure obstacle avoidance was enabled. In the attached log, I was hovering around the intended landing point at about 8:55. It was in P-GPS mode with 15 satellites, and 33.5ft up. From there, you can see that it initiated RTH, but I don't see any notes about obstacle avoidance, etc. You only see the warnings after the obvious collision.

    Do you have any insight on why the sensors didn't kick in? I want to ensure I don't make the same mistake in the future. Thanks!

    Phantom Log Viewer - PhantomHelp.com
     
  2. msinger

    msinger Well-Known Member
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    Your log shows your Mavic crashed onto your driveway. It looks like it might have clipped a tree on the way to the home point.

    Where did you see it crash?

    Crash.png
     
  3. rob968

    rob968 Member

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    That whole map is shifted a little. The original RTH point is basically in the middle of the rectangular portion of the driveway. Right before it went into RTH, it was hovering around the steps on the back patio, which is where the skinnier portion on the right becomes wider toward the left. It ran right into the corner of the house, but a broad portion of it. I was standing on the patio when it happened, and saw the madness go down firsthand. I have video, but it isn't all that helpful since it's pointing straight down.
     
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  4. rob968

    rob968 Member

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    To clarify, it crashed into the "top right" corner of the house, as seen in this view.
     
  5. msinger

    msinger Well-Known Member
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    Can you post the video? It might be helpful.
     
  6. rob968

    rob968 Member

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    It's uploading now, I'll send a link when it's complete. In looking more closely at the video, it just clipped the corner of the house. It looked like a more blatant hit with the naked (horrified) eye.
     
  7. rob968

    rob968 Member

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  8. James Wright-Roberts

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    Hi rob968, sorry this has happened last, I feel your pain! Did you do much damage? What was your RTH altitude set to? From the video this looks like pilot error (sorry) if RTH failsafe is activated the Mavic will ascend straight up until it reaches a predetermined altitude for return to home (I think the default is 30 metres) this didn't happen? As a pilot you can still give control inputs as this is happening, is this what happened? Did you have your hands on the sticks at the time?

    Sent from my SM-N920C using MavicPilots mobile app
     
  9. rob968

    rob968 Member

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    I agree, it was pilot error. I checked in the app and it looks like the default RTH altitude was set to 0, which I'm assuming means maintain current altitude at time of RTH? My hands were on the sticks, but when auto RTH initiated, I didn't feel like I had any control. I pushed "pause", but it had not effect. The auto RTH really caught me off guard and I only had a couple of seconds to react before the impending impact, so I was not proficient enough to cancel it that quickly, or right the path.

    I suppose my biggest question is why the obstacle avoidance sensors didn't do their thing during the auto RTH. From what I've read, it should have at least stopped the bird?

    There wasn't a great deal of cosmetic damage, rather just a couple of damaged props. Unfortunately, I'm getting a gimbal overload error which won't seem to clear. I moved the gimbal around by hand and it seems free, but no love. I check the 3 gimbal "stops", and I'm good with the front two tabs. There is supposed to be a single tab on the rear side of the gimbal, but this either broke off or was broken off beforehand. When I opened the box (new), the gimbal dome and locking piece were unseated, so who knows what sort of beating it took during shipment. I also wasn't knowledgeable enough to know to look for that (now missing) tab, so it's possible it was broken during shipment. I see no signs of physical contact/damage to the actual camera/gimbal from the crash, but it was a good jolt so anything is possible. So my woes right now are figuring out why the obstacle sensors didn't work just so I fully understand the Mavic's behavior for future flights, and getting the gimbal going again.
     
    #9 rob968, Nov 20, 2016
    Last edited: Nov 20, 2016
  10. msinger

    msinger Well-Known Member
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    The default RTH altitude is 30 meters. That's what your flight log shows the RTH altitude was set to during your flight.

    RTH was auto initiated since your battery was low. You might have missed it, but the DJI GO app should have displayed a prompt and allowed you to cancel that action. Since you did nothing within 10 seconds of the prompt being displayed (or you didn't see it), RTH was auto initiated.

    When the Mavic is further than 20 meters (65 feet) from the home point, it'll first ascend to the RTH altitude before returning home. In your case, your Mavic was only 60.2 feet from the home point. In that scenario, it will only ascend to a max of 32 feet before returning home. Your Mavic did not ascend at all since the current altitude was 33.5 feet at that time. So, it turned itself to face the home point and started flying home at the current altitude (as shown in your video).

    The above is explained in the following section of the Mavic manual:

    RTH.png

    In conclusion, this was part user error and part failure by the Mavic since it was not able to sense the corner of your house. The obstacle sensing is not foolproof though, so it would be better to rely on good piloting skills. Next time, stay clear of all obstacles, take off with a fully charged battery, and pay attention to the prompts displayed in DJI GO as you're flying.

    Note: You will only be able to see RTH altitude when your Mavic is connected to DJI GO.

    Note: Your flight log shows the downward sensors calculated your Mavic was really only 17.3 feet above the ground when RTH was initiated. However, the Mavic goes by the altitude displayed in DJI GO. It's not uncommon for it to be incorrect since it's estimated based on data from the Mavic's internal barometer.
     
  11. dam

    dam Well-Known Member

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    Wow this sucks .. Your sad experience is a good guide for new buyers to thoroughly check their gimbal tabs if they receive in the condition you did.
     
  12. TheLightSpeed!

    TheLightSpeed! Well-Known Member

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    Can you post a pic of the back of the gimbal?

    If your gimbal slid out, it will hide the tab.

    If this is the case, you need to carefully slide the front tabs OUT over the stops, then slide the back down, and then stick the fronts back in


    Sent from my iPhone using MavicPilots
     
  13. TheLightSpeed!

    TheLightSpeed! Well-Known Member

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    Also, is it me, or did it look like a child was operating the drone?


    Sent from my iPhone using MavicPilots
     
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  14. dam

    dam Well-Known Member

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    Shhhh. It was "we man" operating the drone ;)
     
  15. The Editor

    The Editor Well-Known Member

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    Agree with all of members comments above - as you have learnt, unfortunately the sensors and fail-safes are not foolproof and can let you down. They are a kind of an insurance but should not be relied upon over and above piloting skills.
    I think where many new Mavic owners will make mistakes is unboxing and then trusting the machine to look after them if they make an error in flying.
    The best thing anybody can do with this aircraft or indeed any aircraft is get in some serious stick time in an open field environment. Get confident flying in different conditions (windy, calm, gusty, sunny, overcast etc).
    Get to know your platform inside out and also get confident flying nose in where your cyclic control (right stick) will be reversed.
    Remember that all the RTH and sensors are there in the event you have no other option left to you but they can let you down.
    I see people constantly saying 'So I had got to the end of my flight and I initiated RTH to bring it home' - why?
    What is the point in 'risking' RTH when you have full control and sight of your aircraft - it's there as an emergency measure not a way to land your aircraft and 'look cool'
    Sorry you had your mishap but you probably have a much better understanding of the Mavic now.
    We have all crashed at some point and are wiser for it.
    Put in stick time until flying becomes automatic and you don't have to think about it - you will be much more confident for it.
    Good luck. :)
     
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  16. James Wright-Roberts

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    This is an excellent and very thoughtful explanation of what happened, I also learned something from it, so thank you! I didn't know that the RTH behaviour was different Depending on distance from home, somehow I missed this and have never been in a position to find out for myself.

    The only thing I could possibly add is looking at the flight video it looks like you only just clipped the edge of the building (maybe even just with the props) this said the majority of the collision avoidance camera view probably wouldn't have seen the impending doom!

    I think it was unfortunately just the perfect storm, and lots of little things came together to cause the crash.

    I think you've got a good explanation thanks to msinger. Hope you get it fixed soon..

    Sent from my SM-N920C using MavicPilots mobile app
     
  17. scooot

    scooot Member

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    And this is why I have bought this for £27.I am sure it will fly totally different from the mavic but it will give me the basic stick skills required.I am waiting for my mavic anyway so I will use it as a tool to learn.
    [​IMG]

    Scott


    Sent from my iPhone using MavicPilots
     
  18. Kilrah

    Kilrah Well-Known Member

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    Looks like the trajectory had just the "right" angle for the sensors not to see the corner of the house.

    To cancel RTH you use the RTH button (remote or app), not the Pause button.

    Make sure you've got volume up on your mobile device, the voice announcing RTH is going to kick in in 10 seconds is hard to miss but of course if the device is muted you won't have it.
     
  19. FPVJunkie

    FPVJunkie Well-Known Member

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    My biggest question is why when the OP pressed the "Pause" button did it not stop the Low Battery-RTH function and hover. The manual states that the Low Battery-RTH can be canceled with the pause button. This would have canceled the RTH and allowed the OP to adjust the path further from the house.

    Sorry, I can't view the videos (due to bandwidth restrictions), so I am only going off what was said.
     
  20. msinger

    msinger Well-Known Member
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    The Mavic manual only mentions that Smart RTH can be cancelled with the pause button.
     
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