Vision Positioning System usage

RaptorMan · Feb 3, 2016

I've not flown over water at a low altitude before, but I have a mission I'm thinking about and I'm thinking about flying about 5-10 feet above the water and wanted to know what the deal is with using the VPS while flying over water. There are videos where they say to turn it off but don't give much info about why or under what conditions one should turn it off.

I would think the VPS would be irrelevant above about 10 feet and would like confirmation of that or maybe a more precise elevation where the VPS no longer matters. Under what conditions is it advised to turn VPS off and why?

Brian

Jason Boucher · Feb 3, 2016

The VPS system uses both a camera and sonar to work. Due to the fact that the water will absorb most of the sound that comes out of the sonar the height information coming from that portion will be inaccurate possibly causing a crash.

I also believe (and correct me if i`m wrong) that the reflection of the water may confuse the camera portion of the sensor and return inaccurate height data.

My answer would be to disable VPS whenever flying over water to save yourself from taking a dunk. I would also suggest to stay AT LEAST 15 to 20 feet above the water. It won`t take a big play at 5 to 10 feet to get your bird wet enough to make it swim. It also gives you more time to correct if you run into any issues.

I`d get more information from others before you make a decisions, I don`t have enough experience with the VPS system to assure you that my answer is correct. This is just my best educated guess.

RaptorMan · Feb 3, 2016

Yeah, I guess my issue is that like a lot of things there's a lot of repeating what they've heard but not a lot of actual confirmed information and what I'm trying to get a handle of is the actual concerns and the actual conditions where they might happen.

As I understand it the VPS system is pretty well limited to about 2m or about 6 .5 feet so anything above that the system should have no effect, but I don't know that for sure. If this is so then flying at 10 feet it should not matter whether VPS is on or off, but again, I don't know that for a fact.

Brian

The Editor · Feb 3, 2016

RaptorMan said:
Yeah, I guess my issue is that like a lot of things there's a lot of repeating what they've heard but not a lot of actual confirmed information and what I'm trying to get a handle of is the actual concerns and the actual conditions where they might happen.

As I understand it the VPS system is pretty well limited to about 2m or about 6 .5 feet so anything above that the system should have no effect, but I don't know that for sure. If this is so then flying at 10 feet it should not matter whether VPS is on or off, but again, I don't know that for a fact.

Brian

Have you read the manual?
Try page 18 for starters. Specifically the part about flying over water and it not functioning properly!

Turn it off.

gregdd · Feb 3, 2016

there are also a lot of videos of the inspire losing altitude when flying forward fast and i have seen it myself very often.

RaptorMan · Feb 3, 2016

The Editor said:
Have you read the manual?
Try page 18 for starters. Specifically the part about flying over water and it not functioning properly!

Turn it off.

Yes, and I went back and re-read it which does kind of answer some of my questions.

But, it's not like they've provided a listing like you normally find in the specifications section. From the manual I can sort of glean that the max height is 2.5m but nowhere does it actually say that. The closest you get is the statement "The effective hovering altitudes of the aircraft is from 0 to 2.5m".

There are a couple statements that don't so much support one another as throw some doubt. One statement, under the heading of "So operate the aircraft cautiously when in any of the following situations:", reads "Flying at high speeds (over 8m/s at 2m or over 4m/s at 1m). Another statement reads "Vision Positioning system may not be able to stabilize the aircraft when flying close to the ground (below 0.5m) in fast speed."

But, in so far as my mission plan is concerned if I keep above 2.5m or about 8.2 feet it shouldn't matter if it's on or off. I don't really have the need or desire at this point to fly fast and low but perhaps as my skills improve I can see a few situations where doing that might be advised.

I guess my issue is that the info is less than clear and to a certain extent contradictory. But, if I'm going to be over water at less than 2.5m turning the VPS off is what I should do.

Brian

The Editor · Feb 3, 2016

RaptorMan said:
Yes, and I went back and re-read it which does kind of answer some of my questions.

But, it's not like they've provided a listing like you normally find in the specifications section. From the manual I can sort of glean that the max height is 2.5m but nowhere does it actually say that. The closest you get is the statement "The effective hovering altitudes of the aircraft is from 0 to 2.5m".

There are a couple statements that don't so much support one another as throw some doubt. One statement, under the heading of "So operate the aircraft cautiously when in any of the following situations:", reads "Flying at high speeds (over 8m/s at 2m or over 4m/s at 1m). Another statement reads "Vision Positioning system may not be able to stabilize the aircraft when flying close to the ground (below 0.5m) in fast speed."

But, in so far as my mission plan is concerned if I keep above 2.5m or about 8.2 feet it shouldn't matter if it's on or off. I don't really have the need or desire at this point to fly fast and low but perhaps as my skills improve I can see a few situations where doing that might be advised.

I guess my issue is that the info is less than clear and to a certain extent contradictory. But, if I'm going to be over water at less than 2.5m turning the VPS off is what I should do.

Brian

Be aware that water moves. You may be flying 20 feet above the water one minute and the next minute without you changing the altitude of your aircraft you are only 10 feet above the water due to the swell!

Turn it off - it was never designed for that kind of task and it can be easily fooled.
Again, like GPS and RTH, its a tool, but should never be relied upon.

go fast · Feb 3, 2016

It's not a big deal to turn it off so why even take that chance , besides I wouldn't trust that the Inspire knows a 3 foot difference at that point , just don't chance it .

ianwood · Feb 3, 2016

I love how DJI has more or less abandoned the idea of fixing VPS.

RaptorMan · Feb 3, 2016

OK, two more questions ...

If it's of little value then it could be removed to save weight, but will the firmware have a problem if it's removed or unplugged? And second, about how much does the VPS system weigh?

Brian

PrimeMotivator · Feb 4, 2016

The VPS system works at a certain frequency where a signal is sent out and a picture is taken every few milliseconds. If the VPS system is not facing directly down because it is at speed or it countering the wind then it won't work very well if at all. If the surface you are flying at low altitude over has no distinguishing features and or absorbs sound then you should turn it off. If you are worried about it dropping in altitude when starting to move forward practice countering that on a level surface first.

Nick Gardner · Feb 6, 2016

I have done a fair bit of high speed low altitude work. Max throttle at approx 3' altitude. Both over water and land. I have found that you need to be flying the crap out of the aircraft. Don't assume anything, and use all of the tools available to you. If looking forward at high speed and low altitude the camera can be one of your best judges of height. It's very hard to tell how high you are once you get more than 100' away, and a very small dip in altitude can result in a bad crash fast at max speed. When doing high speed follow work from a car, the closer you can be to the aircraft the better.

Mytchak · Feb 12, 2016

RaptorMan said:
I've not flown over water at a low altitude before, but I have a mission I'm thinking about and I'm thinking about flying about 5-10 feet above the water ...

My suggestion is to simply use your best judgement. Here's my first attempt over water. I am on shore while my father in law tows my son. VPS was on and during the shooting, I simply used my best judgement. 5 to 10 feet over water at 20 MPH is **** scary and leaves very little room for error. Simply use your best judgement - if you feel comfortable flying lower, go for it. If not, throttle it up and get to where you are comfortable.

Just my two cents...