RTH Settings

[Blackwatch1812]

I'm new to drones with new Mavic 2 Pro. I live on a mountain, elevation 4800 ft above msl, and about 800 feet above the valley floor I'd like to fly over. I presume once I leave the mountain I need to descend to 400 ft agl. If I'm taking off from the top of my mountain, I don't quite understand what settings I need to change, e.g., rth altitude, max flight altitude, and rth at current altitude - what do these need to be at to get rth to come back up correctly?

 

[msinger]

The altitude displayed at the bottom of DJI GO is the altitude above or below the takeoff point. When you ascend, that value increases. When you descend, that value decreases. If you fly below the takeoff point, that value will be negative.

The RTH Altitude is the altitude above the takeoff point. If you want your Mavic to fly back to the home point at 200 feet above the takeoff point, then you should set the RTH Altitude to 61 meters.

What's a safe altitude for the RTH Altitude? Find the tallest obstacle above the takeoff point and add 50 feet or so.

When RTH is initiated, the Mavic will ascend to the RTH Altitude before returning home. If the current altitude is negative, it will ascend up to 0 feet and then up to the RTH Altitude.

 

[Blackwatch1812]

Thank you, that is very helpful. Not having tried it yet, I wasn't aware the altitude would go negative. makes sense. Do I need to set a max flight altitude, or just leave that? I presume that too relates to the takeoff point, would that be correct?

 

[msinger]

Do I need to set a max flight altitude, or just leave that? I presume that too relates to the takeoff point, would that be correct?

Yes, it's the altitude above the takeoff point. You should only set it to a lower altitude if you want to be restricted for some reason. I personally set it to the max and manually restrict myself from flying too high.

 

[John235]

Raises the question: do you go illegal if RTH is set to 200, and initiated while at -400 ft? Wouldn't the drone climb to 600 ft AGL before returning?

 

[tcope]

Raises the question: do you go illegal if RTH is set to 200, and initiated while at -400 ft? Wouldn't the drone climb to 600 ft AGL before returning?

RTH altitude is based on the homepoint/take off position... which is 0. So 200' RTH is 200'. If you fly down to -400' and initiate RTH, the Mavic rises to.... 200' above the take off point which is still 200'.

What you are incorrectly thinking about is the distance that the Mavic _rises_ to get back to 200' (which is 600' to get there from -400').

 

[Jackcutrone]

RTH altitude is based on the homepoint/take off position... which is 0. So 200' RTH is 200'. If you fly down to -400' and initiate RTH, the Mavic rises to.... 200' above the take off point which is still 200'.

What you are incorrectly thinking about is the distance that the Mavic _rises_ to get back to 200' (which is 600' to get there from -400').

But if he flies out into the valley even at -400 per the app, he is at that point 400 feet AGL over the valley which he said is 800 feet below his take-off point. If he initiates RTH it will climb to an indicated altitude of 200 feet so he will be 1000 feet above the ground of the valley and as he suggests it would not be legal. IMO

 

[Meta4]

But if he flies out into the valley even at -400 per the app, he is at that point 400 feet AGL over the valley which he said is 800 feet below his take-off point. If he initiates RTH it will climb to an indicated altitude of 200 feet so he will be
1000 feet above the ground of the valley and as he suggests it would not be legal. IMO

The idea is to set an RTH height that will clear any obstacles that could be on the path back to the launch point.
If he's flying out over a valley, there aren't going to be a lot of obstacles between the flyer and the drone.

 

[msinger]

Flying over 400 feet AGL is not illegal in the US today as long as you're able to maintain VLOS. But, it will be illegal as soon as the FAA starts enforcing the new rules.

 

[John235]

All true, but suppose the drone is out over the valley at -200 ft, (relative to home) and 100 ft above the ground. If contact with the rc is lost, or if the battery goes low, RTH would initiate. The drone would ascend 400 ft to +200 (relative to home). That would put it 500 ft above the ground as it starts it's return. Correct? Does that not make the drone illegal until it gets closer to home? Illegal, or at last above 400 ft AGL, depending on the current state of the regs.

 

[msinger]

The drone would ascend 400 ft to +200 (relative to home). That would put it 500 ft above the ground as it starts it's return. Correct? Does that not make the drone illegal until it gets closer to home?

No. See post #9 above.

 

[Meta4]

All true, but suppose the drone is out over the valley at -200 ft, (relative to home) and 100 ft above the ground. If contact with the rc is lost, or if the battery goes low, RTH would initiate. The drone would ascend 400 ft to +200 (relative to home). That would put it 500 ft above the ground as it starts it's return. Correct? Does that not make the drone illegal until it gets closer to home?

And post #8.
Why would someone want to set such an inappropriate RTh height for that situation?

 

[Jackcutrone]

Flying over 400 feet AGL is not illegal in the US today as long as you're able to maintain VLOS. But, it will be illegal as soon as the FAA starts enforcing the new rules.

I was referring to flying under the new rules.

 

[msinger]

I was referring to flying under the new rules.

Since the new rules are not being enforced yet, you won't be breaking the law if you choose not to follow the new rules.

 

[John235]

And post #8.
Why would someone want to set such an inappropriate RTh height for that situation?

You are appealing to the use of common Sense. That is not as common affliction as we would all hope. In such a situation, I would not need a failsafe height of 200 ft. But change the difference in altitude between home and the valley sufficiently, and even at a RTH height of only 30 ft, it would still be possible to be above 400 ft AGL, even momentarily.

 

[Blackwatch1812]

You all are discussing and having the same thoughts I've been sorting through. Going down the mountain and keeping it manually at 400 ft agl or below isn't a problem (there are some near-100 ft tall trees to avoid); but if the rth algorithm is for the Mavic to rise straight up above the takeoff point and then return at that altitude, it's going to have to rise to at least 900 feet to clear obstacles, and therefore is probably not feasible to use. If on the other hand it follows the exact same levels and route I take bringing it down but at an increased altitude, e.g., +50-75 feet, that's a different story. It's starting to feel like the best option in my case may be to not use rth - but I greatly appreciate the conversation as I come to understand both the rules and the protocols. Thanks!

 

[John235]

Meta4 raised an excellent point that a responsible pilot using common sense would not set a RTH of 200 ft when flying down a mountain where RTH has the potential to put the bird above 400 ft AGL. I was thinking that this makes good sense, and factors in to the pilot's planning.
Then I remembered my recon waypoint mission around my huckleberry patch. The difference in altitude between the low point and high point of that route is only about 50 ft, so it is a no worry to set my RTH to 200 ft. However, if that patch were on another section of my property, the difference would be about 350 ft. I must set the failsafe height in case something happens along the waypoint route, but in that case, the route would be difficult to program, accounting for ground heights all around, and for tree heights. Additionally, I would be taking from near the high point of the route. If a low battery on the drone were to cause a RTH while over the low point, it would be easy for me to push that limit. Others may be in similar situations on terrain even more extreme. The point is to be smart in route planning, takeoff location and in battery maintenance.

 

[John235]

You all are discussing and having the same thoughts I've been sorting through. Going down the mountain and keeping it manually at 400 ft agl or below isn't a problem (there are some near-100 ft tall trees to avoid); but if the rth algorithm is for the Mavic to rise straight up above the takeoff point and then return at that altitude, it's going to have to rise to at least 900 feet to clear obstacles, and therefore is probably not feasible to use. If on the other hand it follows the exact same levels and route I take bringing it down but at an increased altitude, e.g., +50-75 feet, that's a different story. It's starting to feel like the best option in my case may be to not use rth - but I greatly appreciate the conversation as I come to understand both the rules and the protocols. Thanks!

Most of us would probably be flying manually in a case such as this, but suppose you want to film a waypoint route that covers terrain in which the difference in height along your route is say, 350 ft. To account for battery failure at any point along the route, you might need an RTH of as much as 350 ft. More, if there are trees, wires or structures to account for. careful calculation of height differences and in placement of the home point would be critical. Flying a mission without RTH could be risky.

 

[FormerMember07122019_2]

From a practical point of view I would assume one would only use RTM in extreme circumstances i.e. “in case of emergency “. If that is true I’m pretty sure the drone police might cut you some slack similar to the police giving leeway for speeding if you are taking someone in critical condition to the emergency room. I know that dead drones don’t equate to dead people but you get my point.

 

[RTI Glen]

I did not see anyone talk about the horizontal distance
From the mountain or cliff.
Let's say you are on the top of a 1000 ft cliff or mountain and you fly out 200 ft and and the GL is now 1000 ft below you. I believe you are OK out to 400 ft but past that you exceeded the legal limit. The height above ground level applies to horizontal as well as vertical. You OK if the ground is 400 ft or less in any direction except above you !
What do you guys think ?