Andrew F
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They are for forward and sideways stability. Not really elevation.
Mavic loses height
- Thread starter barry christie
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- mavic loses height
Could be something to do with firmware but I would then have expected to see huge numbers of people feeding back that it was an issue! As far as calibration is concerned I've recalibrate everything I think I can recalibrate. Hopefully DJI are monitoring these posts and at the very least undertaking their own tests to see if a software / hardware issue exists and then do something to resolve. If I was able to a sort of scientific test in as much as have it hover against a background with a tape measure to see the amount of height loss over x seconds maybe that would help. I guess I might be able to record the display as well but as its in meters maybe not accurate enough. Im very busy at work which doesn't help 
Could be something to do with firmware but I would then have expected to see huge numbers of people feeding back that it was an issue! As far as calibration is concerned I've recalibrate everything I think I can recalibrate. Hopefully DJI are monitoring these posts and at the very least undertaking their own tests to see if a software / hardware issue exists and then do something to resolve. If I was able to a sort of scientific test in as much as have it hover against a background with a tape measure to see the amount of height loss over x seconds maybe that would help. I guess I might be able to record the display as well but as its in meters maybe not accurate enough. Im very busy at work which doesn't help
I really doubt DJI is monitoring these posts, they're probably busy enough with issues people bring to their attention directly. Once I have some time and maybe a chance to figure out how to make it happen or not happen reliably I'll start a case with DJI and see if they can sort it out.
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I was just out testing some other stuff and noticed it going up and down quiet a bit. Not sure if this video will show but it was going between 30 and 33ft in altitude back and forth.
https://photos.google.com/share/AF1...?key=Q1drRTNqdlJkTmc0c01OR1lqM3ZZZ1cxQm1Xc2ZB
https://photos.google.com/share/AF1...?key=Q1drRTNqdlJkTmc0c01OR1lqM3ZZZ1cxQm1Xc2ZB
I guess at that height it's possible there could be wind knocking it around a bit
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Yes, there was some wind and no doubt that it plays some role. However, it really didn't move much at all laterally. The video it was taking was holding nicely over a spot. It was just going up and down which is a bit odd and by 3 feet which is concerning if you were hovering say 2 feet over some brush.
I flew today and remarkably it was holding position having got out the camera to film it - must have got scared and decided to do what it's supposed to! So now I'm no wiser will have just monitor and see!
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It does seem like it doesn't happen every time, but may not be to do with wind. Right now I'm wondering if it might have to do with taking off quickly.. As in when I take off I always rise to 10 meters so it can take the precision landing photo, and now that I'm getting more confident with the Mavic I've been doing that quite quickly, and then I notice the lowering in altitude.. but on my last couple flights I rose to 10 meters more slowly and it seemed to be stable. I'll have to do more testing to be sure.
Andrew F
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O.K. Here are my findings.
I spent about two hours testing all sorts of scenarios with regard to the subtle elevation changes we're experiencing.
1. This Mavic Pro is an AMAZING piece of technology. I'm just shocked at how far consumer drones have come in a relatively short amount of time. Unless you are seeking "perfection" with good lighting the OPTI mode provides an amazing amount of control. I turned off the sonars to experience plain ATTI and I'm so happy I don't need to use that in close quarters ever again. Kudos to DJI on the amazing advances.
2. Even when "rock solid" - indoors, no wind, apparently no slow rise or fall, full Opti, etc. there IS going to be a subtle moving of the video frame. At least with the current technology, the "battle" between the gimble and the drone trying to be stable creates just a subtle and perceptible movement. However, it is very minor. If you need absolutely NO frame movement for video, I don't believe you will accomplish this with the Mavic Pro in the air. You need a real tripod.
3. Speaking of "Tripod Mode" - I've decided it's really a bad name. The overall stability does not change. The mode simply reduces the effects of the stick input to allow for more subtle pans and slides. So don't think that tripod mode is actually making for a more stable video platform.
4. I noted during my tests that unlike previous times when I noted my Mavic slowly descending, I was consistently experiencing slight rising of the drone. About 3 inches in a minute was what I measured. For 99% of the applications (I'm guessing) this slow rise would be considered irrelevant. But it is there - at times. Sometimes it went away almost completely and all I can think is that the temperature / barometric pressure and sonars found a happy medium.
5. I'm guessing that the sonar software tries to lock the "current" position rather than estimating the current height and trying to maintain that current height. This is a subtle but significant difference. If this is in fact what it is doing, then there is hope for a firmware upgrade to help solve this "elevation drift" - but only when relatively close to a flat surface. So, in short, the Mavic should take a ground distance measurement and "lock" that (unless there is stick input) and try to maintain that distance rather than the "current" height.
6. Even if #4 was a "distance lock" - the sonar clearly has a variance in measurement that I'm guessing is about + or - 2.5 inches at maybe 10 feet. Obviously that variability increases and decreases with overall distance from the ground. I don't think the sensors being used could measure much more precisely than that.
7. I'm unclear about the barometric pressure being used for elevation control. If it is being used in conjunction with sonar, then that might explain some of the elevation drift issues if those readings don't precisely agree (which they likely won't most of the time). But the reality is that barometric pressure changes and the air and Mavic temperature could affect that measurement. It "seemed" to me that as the Mavic warmed up, the elevation drift moderated, but I was getting sporadic results in that regard.
So, in short, I think we need to live with a bit of elevation drift. Elevation is the poorest GPS dimension (and intentionally designed that way), the sonar is not super precise - especially the higher you get, and barometric pressure naturally deviates - especially with temperature variations. If you need a rock solid video platform where elevation drift is not acceptable, I don't think the Mavic Pro is your solution - but I also doubt any other flying drone will provide that without significantly more video stabilization built in.
Hope this helps.
I spent about two hours testing all sorts of scenarios with regard to the subtle elevation changes we're experiencing.
1. This Mavic Pro is an AMAZING piece of technology. I'm just shocked at how far consumer drones have come in a relatively short amount of time. Unless you are seeking "perfection" with good lighting the OPTI mode provides an amazing amount of control. I turned off the sonars to experience plain ATTI and I'm so happy I don't need to use that in close quarters ever again. Kudos to DJI on the amazing advances.
2. Even when "rock solid" - indoors, no wind, apparently no slow rise or fall, full Opti, etc. there IS going to be a subtle moving of the video frame. At least with the current technology, the "battle" between the gimble and the drone trying to be stable creates just a subtle and perceptible movement. However, it is very minor. If you need absolutely NO frame movement for video, I don't believe you will accomplish this with the Mavic Pro in the air. You need a real tripod.
3. Speaking of "Tripod Mode" - I've decided it's really a bad name. The overall stability does not change. The mode simply reduces the effects of the stick input to allow for more subtle pans and slides. So don't think that tripod mode is actually making for a more stable video platform.
4. I noted during my tests that unlike previous times when I noted my Mavic slowly descending, I was consistently experiencing slight rising of the drone. About 3 inches in a minute was what I measured. For 99% of the applications (I'm guessing) this slow rise would be considered irrelevant. But it is there - at times. Sometimes it went away almost completely and all I can think is that the temperature / barometric pressure and sonars found a happy medium.
5. I'm guessing that the sonar software tries to lock the "current" position rather than estimating the current height and trying to maintain that current height. This is a subtle but significant difference. If this is in fact what it is doing, then there is hope for a firmware upgrade to help solve this "elevation drift" - but only when relatively close to a flat surface. So, in short, the Mavic should take a ground distance measurement and "lock" that (unless there is stick input) and try to maintain that distance rather than the "current" height.
6. Even if #4 was a "distance lock" - the sonar clearly has a variance in measurement that I'm guessing is about + or - 2.5 inches at maybe 10 feet. Obviously that variability increases and decreases with overall distance from the ground. I don't think the sensors being used could measure much more precisely than that.
7. I'm unclear about the barometric pressure being used for elevation control. If it is being used in conjunction with sonar, then that might explain some of the elevation drift issues if those readings don't precisely agree (which they likely won't most of the time). But the reality is that barometric pressure changes and the air and Mavic temperature could affect that measurement. It "seemed" to me that as the Mavic warmed up, the elevation drift moderated, but I was getting sporadic results in that regard.
So, in short, I think we need to live with a bit of elevation drift. Elevation is the poorest GPS dimension (and intentionally designed that way), the sonar is not super precise - especially the higher you get, and barometric pressure naturally deviates - especially with temperature variations. If you need a rock solid video platform where elevation drift is not acceptable, I don't think the Mavic Pro is your solution - but I also doubt any other flying drone will provide that without significantly more video stabilization built in.
Hope this helps.
Thanks for doing all this testing! Yes with regard to tripod mode I thought it was clear in the manual that all it does is make the controls less sensitive. Be careful with it because it can be disabled by an attempted landing or other things and then all of a sudden and unexpectedly your controls are zippy again. I crashed indoors by flying over a railing. It thought I wanted to land and that took it out of tripod move so my next move made it slam in to the ceiling.
iPhone 6S
iPhone 6S
Just had this happen to me over the weekend in Orange County CA- caught me off guard a bit. Curious if something changed with one of the firmware updates because I had about 25 flights prior with no issue of losing altitude.
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Andrew F
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Hmm, I received a replacement unit on Monday.. flew last evening.. and the vertical stabilty was not good. At hover it varied from 4 ft to 6-7 height. And was wandering in about a 3 ft diameter. My original unit was rock solid.
Unit was was calibrated and had 17 satellites
Unit was was calibrated and had 17 satellites
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Andrew F
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I'm betting on dusk confusion - at least for the wandering. The elevation variability still comes and goes for me for no clear or consistent reason. I'm fine with it as it is a slow rise or fall and I'm not doing anything where that matters.
Ultrasonic Sensors are affected by Temperature and Humidity.
Sound waves travel faster in warm humid air and slows down in cool dryer air.
The speed of the Ultrasonic pulses will change as cooler or slightly warmer air passes underneath the Mavic. It can account for an an inch or two of up and down bobbing. I have no idea why some peoples Mavics are moving by several feet.
Rob
Sound waves travel faster in warm humid air and slows down in cool dryer air.
The speed of the Ultrasonic pulses will change as cooler or slightly warmer air passes underneath the Mavic. It can account for an an inch or two of up and down bobbing. I have no idea why some peoples Mavics are moving by several feet.
Rob
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Andrew F
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I believe it is the barometric pressure measurement but as I said, I haven't had a perfect test or troubleshooting effort to absolutely determine this. The sensors are much easier to test as you can turn them on and off easily. Not so with the barometer.
There is no way it is going to hover within inches using Barometric pressure changes. It would need to use Ultrasonic measurements.
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