Flying over water (lakes). GPS issues?

[grahamgee]

Hey guys,

New member here, so i'll do a short intro. Name's Graham, new to the drone game and loving it. do my own photography and have done for many many years now and after a stint away from motion, on a snow trip over the last 6 months my gf hooked me up with a hero3 and I started to gain interest in motion and editing again.

I've picked up the DSLRPros P2 kit, so far, so good. However the other day I went out for an afternoon shoot with a good mate of mine and his boat.

The drone worked fine for the most part, but twice during the shoot, I couldn't send it toward me, we had to drive after it. It would hold altitude and I could control the altitude without a problem. When it was facing me I couldn't send it forward, it would just stay still, when I turned it around I couldn't go backward (to bring it toward me) I could only send it forward.

The normal flight lights were on, and intermittently would change to one set solid red and one set flashing red, then it would come back to green again with no issue.

It was a bit of a scare, as I wasn't really sure what the cause was.

Later on the drive back, we noticed another guy flying a proper RC helicopter over the lake. My mates boat is a Super Air Nautique and the speed and control for the boat is mostly done with its OSD which also has a GPS module that shows him where he's been. Interestingly enough, there was a fault with a crows-flight line going across land (clearly didn't happen, we were in a boat)

I'm wondering if you think that there was some kind of interference from the helicopter, the boat, both or if it was just a 'hole'.

A point to add, I had it over the local beaches and sent it out quite a ways off shore and had no problem at all getting it back.

Thoughts?

 

[laselvasurf]

Very odd! I've flown over a lake before without issues. See https://www.youtube.com/watch?v=mtTD1Tg1lVk

Were you flying only in GPS mode? I've had GPS mode do some weird things over the years and always switch out to Atti and all is well. My guess is the the compass needed calibration, or you didn't have a good enough GPS lock for some reason. Did you calibrate your compass at that location?

The only unexplained thing is the lack of control. I've never heard of that before...

I highly doubt you were getting interference from the other RC copter since the 2.4GHZ connection of the phantom is quite robust and you were very close when having the issues.

 

[ianwood]

Lakes and ponds are usually pretty still and tend to act like a giant mirror. Your TX signal will bounce off of the lake surface in unpredictable ways and can in the worst of cases arrive at the RX 180 degrees out of phase and knock out the unreflected signal. Diversity helps with this but doesn't necessarily solve it. The further you get, the more likely it will happen. But it should only happen briefly if at all and shouldn't result in a flyaway condition (not 100% certain of this).

I do recall a similar story where someone was flying over water and they had intermittent partial loss of control for a brief period of time.

 

[shrill mute]

I've flown over the water a bunch. Mostly from a boat, all in ATTI mode. I've never had any issues like you describe.

That is very odd.

 

[sar104]

I would have expected water to be a particularly poor reflector at 2.4 GHz.

 

[ianwood]

I would have expected water to be a particularly poor reflector at 2.4 GHz.

Apparently the higher the frequency, the better it will reflect. But it also depends on the angle. Even the salinity can influence it. There's a lot of messy science to it. But my understanding is 2.4GHz will reflect and can cause the same kind of multi-path degradation you see in and around tall buildings.

 

[shrill mute]

I would have expected water to be a particularly poor reflector at 2.4 GHz.

Apparently the higher the frequency, the better it will reflect. But it also depends on the angle. Even the salinity can influence it. There's a lot of messy science to it. But my understanding is 2.4GHz will reflect and can cause the same kind of multi-path degradation you see in and around tall buildings.

That has not been my experience at all.

 

[ianwood]

That has not been my experience at all.

Well, as I've been saying, there are a lot of factors:

The further you get, the more likely it will happen. But it should only happen briefly if at all and shouldn't result in a flyaway condition.

But it also depends on the angle. Even the salinity can influence it. There's a lot of messy science to it.

 

[sar104]

I would have expected water to be a particularly poor reflector at 2.4 GHz.

Apparently the higher the frequency, the better it will reflect. But it also depends on the angle. Even the salinity can influence it. There's a lot of messy science to it. But my understanding is 2.4GHz will reflect and can cause the same kind of multi-path degradation you see in and around tall buildings.

Turns out you are correct - the interaction of 2.4 GHz with water is rather complex. A quick literature survey reveals that there is considerable uncertainty over ε(ν) even without the complication of dissolved solids. Learn something every day.

 

[grahamgee]

Hi guys,

Thanks for the response, it's making a little more sense. I wasn't offshore, it was an inland lake (lake macquarie, Australia) to be exact. It was a very still afternoon.

I've usually been using it around beaches and what not but it seemed strange to me. I've had a few other issues since with lights so I really need to look that up and get on top of it before I'm confident enough to take it out over water again.

 

[grahamgee]

?For the record, from *memory* it was in GPS mode.

 

[Geo74]

I have flown over the open sea to a distance of 2200m without any problem indications and I could go for more if I wasn't afraid. That is my experience so far

 

[grahamgee]

Okay, so the kit was in Phantom mode, so I'm unsure as to exactly what it would have been doing. Why it wasn't in NAZA i'm unsure.

Very odd! I've flown over a lake before without issues. See https://www.youtube.com/watch?v=mtTD1Tg1lVk

Were you flying only in GPS mode? I've had GPS mode do some weird things over the years and always switch out to Atti and all is well. My guess is the the compass needed calibration, or you didn't have a good enough GPS lock for some reason. Did you calibrate your compass at that location?

In any case, am I best to be just using Atti mode with no IOC when flying over water to avoid the GPS issues?

Obviously we're in a boat, so the fly home Fail Safe isn't really going to do much good, as I was calibrating on the sundeck of the watercraft at the time. Now that I look back on it, the calibrations probably didn't do much, but I was getting the green lights to go.

Laselvasurf: Nice footage there, i'm personally not into airchairs myself, I grew up wakeboarding and wakeskating, but I've shot some stuff that is very similar (there's a video on my instagram @grahamgee of a super air nautique if you're interested, I haven't uploaded it to youtube or vimeo yet)

I'm interested to know if you were shooting from a follow (chase) boat still or if you stayed on land to do your shooting. The lake that I'm on, it would still be helpful to have a chase boat, so as riders could keep going if there was an issue like we had with the drone.

 

[Kevinski]

Could this have been a geofence issue? What were the limits and distance from home? attitude mode will allow you to fly outside the geofence.

Thanks,

Kev

 

[max01726]

Were you constantly moving further away from your home point? If so It could be the limits set in the assistant being low which means you can't fly further than what it's set to and the drone will act like it's just hovering when you try and fly it past that set limit, it won't let you

 

[ianwood]

What makes you think this was a GPS issue? This looks much more like a RC signal issue.

 

[grahamgee]

Could this have been a geofence issue? What were the limits and distance from home? attitude mode will allow you to fly outside the geofence.

Thanks,

Kev

Were you constantly moving further away from your home point? If so It could be the limits set in the assistant being low which means you can't fly further than what it's set to and the drone will act like it's just hovering when you try and fly it past that set limit, it won't let you

Thanks guys,

I was thinking about this the other day as I was setting up the unit for Naza-M and took note of the Geofence (I'm assuming you're talking about the range settings you can specify on the assistance software?) and the restrictions were set at 400m high and 1600m away, from where you would calibrate your gps obviously. This would make sense, as we were moving on the boat and it doesn't take long to cover that kind of distance in a straight line running at 21mph.

That being said, am I best to run it in ATTI mode, do I still need to calibrate the GPS on startup with ATTI? What would be the most reliable way to set those distance parameters. Is there a way I can set up the IOC to keep the distances between myself and the drone relative as we move in the boat?

What makes you think this was a GPS issue? This looks much more like a RC signal issue.

I'm new to this, which I covered in the original post, I was just throwing ideas out there to get an idea of what people thought it could be. As it stands, I'm fairly certain after looking at the behaviour of the drone that it was the GeoFence, as I could control the Altitude and could send it toward where the drone was actually calibrated on startup on the back of the boat, but not in the direction toward me.

 

[tom3holer]

Yes, you do indeed need to waite till the GPS is done acquiring sats and has indicated so, by rapid flashing green once in in Phantom mode or twice if in Naza mode.
The IOC will not work without GPS.

Tom

 

[ianwood]

There is nothing in this case to suggest GPS has any role in the issue so I would not bother with any distinction between ATTI or GPS as a means to prevent such behavior in the future. Use either mode as you see fit. The problem is much more likely to be an RC issue than GPS.

As for the calibrations, do not manually calibrate anything on a boat (e.g. IMU or compass). As for the normal startup initialization, you want to try to keep the Phantom as level and still as possible for the first 30 seconds and ideally until it has acquired a home location fix.

 

[grahamgee]

There is nothing in this case to suggest GPS has any role in the issue so I would not bother with any distinction between ATTI or GPS as a means to prevent such behavior in the future. Use either mode as you see fit. The problem is much more likely to be an RC issue than GPS.

As for the calibrations, do not manually calibrate anything on a boat (e.g. IMU or compass). As for the normal startup initialization, you want to try to keep the Phantom as level and still as possible for the first 30 seconds and ideally until it has acquired a home location fix.

Okay, I see your point, I guess I was just curious about the 'safest' setting for the situation i was in over water as a sort of follow up question to the first inquiry.

As far as the home location fix goes, would that not pose the same issues, given that I was controlling it from within the boat, shooting with the boat as it moved? It's going to hit the geofence as described at one point or another after I set that home point right?

I've not had any RC issues what so ever aside from the issue I have described. It seemed strange that it was happening over water, So I guess now i'm looking to see what 'safe' distances are to set within the software.