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How to fly at altitude below starting alt without crashing? Altitude Accuracy?

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Does everyone agree the altitude accuracy of the H is 10-30' and that the altitude is relative to the starting altitude, i.e. starting alt = 0' despite actual?

Also, does everyone agree the altitude reading can change by 10-30' during a flight?

If so, does anyone have advice on how to safely fly at an altitude 50-75' below the starting alt without hitting anything? It's very difficult to judge the distance from an obstacle and/or the ground when looking down at a steep angle. Flying using video only seems a little risky.

The reason I ask is I'd like to take a CCC flight video over and down an ocean side cliff which is ~100' high and would like to get down to within 25-30' of the ground/water (deserted area).

Any ideas or experience?
 
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rdonson

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It sounds like you need a spotter with you when you setup you CCC points, The spotter can tell you from their vantage point if things look safe. Set the CCC points that way. Go back, then fly the CCC course making sure that the flight course is good. If you're confident, the third flight is when your attention is on the camera and creating the video.

That's how I approach it anyway. YMMV.
 

Steve Carr

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When you start the motors the altitude is reset to zero. As the temp inside the H changes, it seems the altitude reading also changes so it can easily be off 10' after flying for a bit. As you fly down into a valley the reading will show a negative number for alt. I would certainly suggest staying at least 30' from anything in the flight path. Remember, if you fly down into a valley the H has to fly back up again to return and you need enough battery power to make it to the top.
 
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It sounds like you need a spotter with you when you setup you CCC points, The spotter can tell you from their vantage point if things look safe. Set the CCC points that way. Go back, then fly the CCC course making sure that the flight course is good. If you're confident, the third flight is when your attention is on the camera and creating the video.

That's how I approach it anyway. YMMV.
Thanks for the input!

I hoped I could avoid having to make the difficult and hazardous trek down the cliff side but it sounds like that is really the only way to be sure.

I flew today in a park and the altimeter was off by ~20' when it returned from its first flight. This is So Calif so temp was an ideal 72F, bird stored at ~same temp and wind was calm. No major changes in Baro as weather is not changing. I was very surprised the altitude was off by that amount after a 15min flight.
 

Steve Carr

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On those occasions where I need a reasonably accurate reading, I start the motors and watch the altimeter for a minute or so. If it starts to drift I restart the motors to zero out the reading again. That seems to help. I've found the sun tends to heat up the bird and the added heat from the electronics and the battery increase the temp inside the H. In any case, trying to determine the altitude while looking down a hill can be tricky. Pointing the camera straight down might help.
 
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When you start the motors the altitude is reset to zero. As the temp inside the H changes, it seems the altitude reading also changes so it can easily be off 10' after flying for a bit. As you fly down into a valley the reading will show a negative number for alt. I would certainly suggest staying at least 30' from anything in the flight path. Remember, if you fly down into a valley the H has to fly back up again to return and you need enough battery power to make it to the top.
Thanks Steve

I'm hesitant to use this bird as I had intended (to go where I didn't want to go myself) after seeing the significant altitude variations. I've seen some amazing videos flying between obstacles going downhill but I guess you have to be willing to take the risk of hitting something. In my case I would lose the bird in the ocean if I couldn't judge the height. With the waves at 5-6' and the 25-45' altitude variation (absolute accuracy 10-20' + drift of 15-25') this seems a no-go
 

Steve Carr

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If you are looking for close-in shots then yes, it could be risky. Even if you are on the shore it can be risky if a big wave comes in. I've seen videos on Youtube of that very thing.
 
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PatR

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Getting those great videos often comes down to having an attitude of "no guts, no glory". High risk videos always are obtained at high risk and those unwilling to take the risk will be hard pressed to find a "safe" way to do it. Personally, I would not want to test CCC accuracy when flying at a negative altitude but I would hand fly the location once or twice to establish a "through the lens" view where I established what a safe altitude looked like from the camera and then go for broke if I felt good about it. Perspective from above can be pretty tough. Using aircraft shadow can be helpful but a cresting wave can ruin the day. Worst case is you back out of it before getting to close to the edge of your envelope.
 
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This fourm is so informative for a newbie like me. Please confirm the basic of this thread: is it ok/safe to fly at negative altitude, what should i be aware of? I have several scenes in mind that are at negative altitude.
Sorry to change direction of thread, Carlz.
 

CraigCam

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From hours of work and observation I can safely say that in CCC replays, your altitude and general mission can deviate by many feet. As rdonson stated a spotter is needed but that sounds impossible. There is in theory a limit to the lowest altitude and that seems more consistent when using good 3rd party CCC companion apps. The other issue I’ve been working on learning and understanding is where you really are relative to your position and perspective. One of the hardest to judge is distance relative to target especially when flying downward and away. I’ve learned that what my naked eye thinks is not that far away seems agonizingly far away once flying towards it. It’s difficult to pick up the needed detail on the ST screen and the lag time doesn’t help. When you see the object you are about to hit in your monitor it’s too late usually to react and cancel the mission and regain control.
 
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From hours of work and observation I can safely say that in CCC replays, your altitude and general mission can deviate by many feet. As rdonson stated a spotter is needed but that sounds impossible. There is in theory a limit to the lowest altitude and that seems more consistent when using good 3rd party CCC companion apps. The other issue I’ve been working on learning and understanding is where you really are relative to your position and perspective. One of the hardest to judge is distance relative to target especially when flying downward and away. I’ve learned that what my naked eye thinks is not that far away seems agonizingly far away once flying towards it. It’s difficult to pick up the needed detail on the ST screen and the lag time doesn’t help. When you see the object you are about to hit in your monitor it’s too late usually to react and cancel the mission and regain control.
Thanks Craig

Very useful feedback
 
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Getting those great videos often comes down to having an attitude of "no guts, no glory". High risk videos always are obtained at high risk and those unwilling to take the risk will be hard pressed to find a "safe" way to do it. Personally, I would not want to test CCC accuracy when flying at a negative altitude but I would hand fly the location once or twice to establish a "through the lens" view where I established what a safe altitude looked like from the camera and then go for broke if I felt good about it. Perspective from above can be pretty tough. Using aircraft shadow can be helpful but a cresting wave can ruin the day. Worst case is you back out of it before getting to close to the edge of your envelope.
Thanks Pat

Sounds like I need to increase my margin of error. 50' feet seems a bit large but may be the only safe way to do it
 
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Thanks everyone for sharing your insights and the very useful suggestions. I'll get that **** shot eventually but it sounds like I need to observe the deviations of my bird a bit more and increase the margin of error
 
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Just one more comment. The Yuneec CCC program drives the TH in sweeping arcs rather than straight lines between way-points. These arcs can cause problems if you haven't taken them into consideration. I know the arcs are there in the horizontal plane; I'm not sure if the arcs appear in vertical planes as well.
 

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I fly both the H and the 920. The H has far better antenna exposure than the 920 does (5.8 at front of camera, 2.4 at top rear of camera) which is relevant because I fly the 920 below launch height as well with no problems. It does have 2.4 antennas inside the body but they are completely enclosed in what I believe to be a carbon fiber enclosure. I kind of disagree with the advisory to keep the aircraft close. Too close over the top of the H and the bottom mount antennas can have the aircraft body get between the transmitter and aircraft antennas to interrupt signal. If you can maintain an angle between you and the aircraft where there remains a pretty clear line for signal between the bottom of the aircraft and the transmitter you'll be off to a good start. Pay attention to the transmitter antenna orientation. Remember they radiate in an exaggerated oval or donut pattern and if you keep them angled upwards while flying below you the aircraft will receive a weaker signal. Adjust them as needed to remain roughly 90* to the aircraft.

Just plan your flight with reasonable clearance separation Allow for a fairly common GPS position error of +/- 3 meters or so. There's no reason to put the aircraft right up against something. They make hand held cameras and macro lenses for that kind of stuff. Don't try to accomplish tasks you don't feel your ready for. Practice the tight stuff in more friendly locations until you know you're good at it. The tight spaces stuff is a lot more difficult and stressful than many understand. When no room is left for error you can be pretty sure there will be an error.
 
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Just one more comment. The Yuneec CCC program drives the TH in sweeping arcs rather than straight lines between way-points. These arcs can cause problems if you haven't taken them into consideration. I know the arcs are there in the horizontal plane; I'm not sure if the arcs appear in vertical planes as well.

Would not adding more waypoints, even if going in a straight line, cause the UAV to fly more precisely? As well, more waypoints in a curve won’t necessarily be more precise as airspeed is a major factor in the UAV’s flight path.
 
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Yes, more waypoints would control the flight path more precisely. However, I think airspeed has very little effect on the CCC flight path since the path does not change direction abruptly as in a mapping software.
 

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