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DO NOT turn off the VPS sensors when flying over water

boblui

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I know this is contradictory to the believe held by many but so far I have not seen any proof that flying over water with VPS on has caused troubles. Whenever reports about drones taking a bath come out, many will quickly jump to the convenient conclusion that the cause is "water confusing the sensors" in some vaguely described ways. The fact is in quite many cases, flight log analysis has proven that the real cause was something else.

I have done a test with my M2P today. Over land and with VPS on, the drone will hesitate after descending to a height of 0.5 meter. You need to confirm your intention to land by holding the throttle stick all the way down for more than one second before the drone will land. Here is the flight log. You can see that I have pulled the stick all the way down momentarily for multiple times but the drone just held it’s altitude :

vps on over land.JPG

This is the response of the drone when VPS is off. The drone will keep responding to the throttle control and descend until it touches the ground. If the throttle stick is held all the way down, it will hit the ground hard :

vps off over land.JPG

What I found today is that if the 3D camera at the belly cannot see any clearly discernable patterns ( I tested it by covering up the camera lenses with tapes ), then the drone will be more conservative and stop descending at a larger height of 1 meter ( instead of 0.5 ). Over the water, this is the situation so my M2P stopped descending further at 1 meter over the water surface despite repetitive fully-down throttle inputs were applied. Had the VPS been off, I probably will need to use the DJI care service . This is obviously a desirable protection mechanism that helps the drone to stay dry so why turn the VPS off ?

vps on over water.JPG


 
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Repeat with the Mini. Will surprise you. Have a float and Care handy.
The mini just lacks 3D vision at the belly. Like M2, it also uses IR sensor to detect distance from the surface below so I cannot see why the behavior will be different. Perhaps you can share some experience and preferrably flight logs ?
 
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You might try those tests again with different/varying water conditions.....

The worse condition is that the water surface is so rough that the infrared light emitted from the belly cannot be reflected back to the sensor making the drone unable to tell how high it is above the water surface. This is equivalent to disabling the VPS sensors and the drone will descend into the water if full throttle down is applied. In such circumstances , turning the VPS sensors on will not help but it wont create problems either. That's why I think they should be left on at all time.
 
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And anything in between chop to glass water, and lest we not forget the sunlight reflecting of the water's surface. It can be just to much for the AC to handle/"confuse".

The system is no way "perfect". It does have it's limitations....
 
.... sunlight reflecting of the water's surface. It can be just to much for the AC to handle/"confuse"....

This sunlight theory has been mentioned by many and yet no one has ever come up with an explanation on why it can cause the drone to descend into the water on it's own.
 
Maybe by causing signal saturations on the sensors? They can only set the parameters so far, and guess what? Nature will toss something outside of that "man made" envelope.
Kind of like when the sun confuses the AC in the "low sun" condition and causes it to halt thinking there is something ion front of the AC. There always limitations on the conditioning of the sensor signals, can't plan for all of them...
 
Maybe by causing signal saturations on the sensors?

It probably will but how will it cause the drone to go into the water ? base on my knowledge on how drones use the output of these sensors, I cannot see how. Perhaps some one can enlighten me on this.

Kind of like when the sun confuses the AC in the "low sun" condition and causes it to halt thinking there is something ion front of the AC.

If this is the mechanism, the drone will stop descending into the water. Many has claimed the opposite, without providing any explanation, let alone evidence.
 
Part one on above, IF it got "confused" (coding error?) thinking it was solid ground.
Anything can be fooled...I'm clutching here, but the nothing is perfect. Period.

Part two above, It could be anything, some confluence of data, to much data, to little data, too much light, too little light, who knows. It's not just what data goes "out", it;s also the data that "comes in". Stuff happens.

With what they put into these machines is astonishing, but yes, they have limits...

Just like an inner tube.....
 
Part one on above, IF it got "confused" (coding error?) thinking it was solid ground.
Assuming that you are right and the drone thinks that it is flying over solid ground. How will it make the drone descend onto the surface and get surprised ?
[/QUOTE]


Part two above, It could be anything, some confluence of data, to much data, to little data, too much light, too little light, who knows. It's not just what data goes "out", it;s also the data that "comes in". Stuff happens.
With so many unknowns may be we should just stop flying drones.
 
Part a as in if it is over water, there's your issue.

Part b You can if you want to. It's Just some folks have to realize that nothing is perfect. Especially made by a human being.

Now, as to why fly? It's fun. But we also realize that we are not running an rc car on the ground, or a boat on the water.( there's that word again!), we are flying in the air, fighting gravity. Now, yes, there is a lot going on to keep that little piece of plastic in the air. And guess what? It's all made by a human being.

You do the math.
 

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