Height setting

gannp · Jan 14, 2023

Obvious I guess to most but I just need clarification.

When i set a height is that AMSL or AGL.

Does the drone [mini 2] take in to account rising terrain and continue rising at the preset height?
What happens if it encounters steeply rising terrain?

For simplicity, if I set 400ft height, and stand on a 1000ft high mountain, then fly out over sea level flat fields below, do I maintain 1,400 ft? Does the drone realise I have contravened CASA regulations and automatically descend to remain legal? Conversely if I am on those same sea level fields and encounter the 1000ft mountain does the drone rise?

Sorry for such drone 101 questions but best to be sure in my own mind.

Might as well toss this one in at same time.
I have been wanting to buy a propeller guard for the Mini 2 but haven't seen any advertised.
Is it available
Is flight performance degraded to any noticeable degree
PS Cancel request for prop protector info as it seems to be adequately answered in another thread I have just stumbled upon. If I read correctly there are more minus's than plus's to using them, and the basic consensus is they aren't worth it.

GFields · Jan 14, 2023

No. It is based on the take-off point

Prop Guards can be found on Amazon

gannp · Jan 14, 2023

OK so above AGL but in my hypothetical scenario "if I set 400ft height above my take off point, which is while dstanding on a 1000ft high mountain, then fly out over sea level flat fields below, do I maintain 1,400 ft [which is still only 400 ft above my tgake off point]? Does the drone realise I have contravened CASA regulations and automatically descend to remain legal? Conversely if I am on those same sea level fields and encounter the 1000ft mountain does the drone rise or simply maintain the initial MSL 400ft?"

GFields · Jan 14, 2023

gannp said:
OK so above AGL but in my hypothetical scenario "if I set 400ft height above my take off point, which is while dstanding on a 1000ft high mountain, then fly out over sea level flat fields below, do I maintain 1,400 ft [which is still only 400 ft above my tgake off point]? Does the drone realise I have contravened CASA regulations and automatically descend to remain legal? Conversely if I am on those same sea level fields and encounter the 1000ft mountain does the drone rise or simply maintain the initial MSL 400ft?"

I'm not a fan of Drone U, but maybe this will help you

mobilehomer · Jan 14, 2023

Simply, NO your drone does not know its altitude. It only reports how high it is above takeoff. It uses barometric pressure to compute this. If you take off at 1000' and climb to 400', then fly over the sea level flat fields below, the drone only shows 400' altitude.

Yorkshire_Pud · Jan 14, 2023

gannp said:
OK so above AGL but in my hypothetical scenario "if I set 400ft height above my take off point, which is while dstanding on a 1000ft high mountain, then fly out over sea level flat fields below, do I maintain 1,400 ft [which is still only 400 ft above my tgake off point]? Does the drone realise I have contravened CASA regulations and automatically descend to remain legal? Conversely if I am on those same sea level fields and encounter the 1000ft mountain does the drone rise or simply maintain the initial MSL 400ft?"

In terms of your question the drone has no knowledge of its height above the ground beneath it. *
So, if you sent the drone up to 400ft above that mountain top and then flew it out over that plain it will be 1400ft AGL.
If you take off on the plain and send the drone up to 400ft then fly towards the hill the drone will crash into the hill at a height of 400ft relative to the take off point.

* However some drones are equipped with a limited-range downwards-looking sensor that can read AGL when the ground is close enough. Some of those do display that information, others do not.
Some DJI drones have what is called "landing protection" which can, if the drone is moving slowly enough, force the drone to climb but I think that should not push the drone above the height limit set in the app.

lensimages · Jan 15, 2023

gannp said:
Obvious I guess to most but I just need clarification.

When i set a height is that AMSL or AGL.

Does the drone [mini 2] take in to account rising terrain and continue rising at the preset height?
What happens if it encounters steeply rising terrain?

For simplicity, if I set 400ft height, and stand on a 1000ft high mountain, then fly out over sea level flat fields below, do I maintain 1,400 ft? Does the drone realise I have contravened CASA regulations and automatically descend to remain legal? Conversely if I am on those same sea level fields and encounter the 1000ft mountain does the drone rise?

Sorry for such drone 101 questions but best to be sure in my own mind.

Might as well toss this one in at same time.
I have been wanting to buy a propeller guard for the Mini 2 but haven't seen any advertised.
Is it available
Is flight performance degraded to any noticeable degree
PS Cancel request for prop protector info as it seems to be adequately answered in another thread I have just stumbled upon. If I read correctly there are more minus's than plus's to using them, and the basic consensus is they aren't worth it.

Sorry but I disagree about prop protectors, I use them when I photograph the interior’s of buildings and they definitely work . I have seen my mini 2 with them fitted bounce off the walls when it drifted to close, and no damage to drone enabling me to continue taking photographs. I don’t use them anywhere else so cannot comment about flying outdoors, but indoors they are a boon, cheers Len

gannp · Jan 15, 2023

lensimages said:
Sorry but I disagree about prop protectors, I use them when I photograph the interior’s of buildings and they definitely work . I have seen my mini 2 with them fitted bounce off the walls when it drifted to close, and no damage to drone enabling me to continue taking photographs. I don’t use them anywhere else so cannot comment about flying outdoors, but indoors they are a boon, cheers Len

Basically we agree. I just didn't qualify my answer. I was only looking at outdoors as indoors I have no use for the drone.
From what I understand now they are very good indoors but due to weight [taking it over the allowed max. weight], drag, battery life, and wind resistance they are not recommended outdoors.

KB9Radio · Jan 15, 2023

gannp said:
OK so above AGL but in my hypothetical scenario "if I set 400ft height above my take off point, which is while dstanding on a 1000ft high mountain, then fly out over sea level flat fields below, do I maintain 1,400 ft [which is still only 400 ft above my tgake off point]? Does the drone realise I have contravened CASA regulations and automatically descend to remain legal? Conversely if I am on those same sea level fields and encounter the 1000ft mountain does the drone rise or simply maintain the initial MSL 400ft?"

The drone would continue to fly at 1400 feet AGL (400 above take off), but would not be legal. Legally you would have to drop to 400 ft AGL asap.

Yorkshire_Pud · Jan 15, 2023

With regards to AMSL, the drone might monitor it, via the barometer, and I think I have read of some DJI drones issuing a warning that a take off is being attempted near the AMSL ceiling for the drone but they do not otherwise display any information concerning AMSL in the app.

Every height limit you set in the app is relative to the take off point, e.g maximum height, RTH height and, if your drone has it, probably waypoint heights. In terms of flying within legal height limits it is up to the pilot to maintain AGL.

There is one other height limit that you might encounter if you fly up 'tall' mountains, DJI firmware has an absolute maximum height of 500m relative to the take off point, that can not be broken unless the drone goes wonky or the firmware is hacked. It would take a long time to get up there and, perhaps more importantly, safely down from there, especially if you are battery watching on the way down.

JoelP · Jan 15, 2023

Don’t worry about asking a 101 level question. This is a question asked here on a regular basis.

A follow-on question would be how can I fly near a rising or descending slope and maintain legal elevation? The answer is that you either have to study a map that shows the elevations and memorize it or use a 3rd party tool such as Litchi, which I recall is available for the Mini2. If you purchase Litchi you can preplan your flight and set the elevation at a series of waypoints. Then you can preview this on your PC with Vitual Litchi and Google Earth Pro to see how that preplanned flight would look or if any leg of your flight would have you encountering the ground. You would then modify that flight plan and run that preplanned mission to have your Mini 2 at the desired elevation as it flew about that hilly terrrain.

Have fun flying!

moldorf · Jan 15, 2023

the best explanation I've seen here: imagine a 400' long string suspended from the bottom of the drone in a straight vertical line that isn't affected by wind or speed. Whenever that string wasn't touching the ground you'd technically be violating regulations

I suppose they could come up with an optical system for the bottom of a drone coupled with a very precise barometer and super GPS linking including complete mapping all fed into an analytical motherboard that could tell you what your actual elevation is above the ground. Of course, the drone would probably weigh 30 pounds and cost $70,000

Dbez1 · Jan 15, 2023

Realistically, if you make an effort to eyeball it to keep within legal limits, I doubt if the FAA would complain. I liked moldorf’s string explanation.