Max height for RTH

[hopeful21]

Does anyone know what a Mini 3 would do on a RTH caused by loss of signal if the max height and RTH height were set to 50m and, on the return, trees got in the way at 51m?

Would it automatically brake because it's not allowed over 50m, or would it have to try and go around?

 

[LoudThunder]

Does anyone know what a Mini 3 would do on a RTH caused by loss of signal if the max height and RTH height were set to 50m and, on the return, trees got in the way at 51m?

Would it automatically brake because it's not allowed over 50m, or would it have to try and go around?

You set the RTH much higher that any possible obstacles. I'm not advocating any outrageous height, just enough to ensure you don't have this issue... But I imagine that if the M3 found itself in this situation, it would just hover... And if you can't get control, it will ultimately land in the trees when the battery dies...

 

[karlblessing]

RTH doesn't bother with avoidance. If you have lost signal behavior set to RTH it's just going to go straight up to the specified height, and b-line it right back to the homepoint. If RTH isn't such a fair bit higher than obstacles, it will just run right into them.

 

[Daytona500]

where do you get that info from as far as I know RTH does not turn OA off and I think you can set it to go around obstacles

 

[karlblessing]

where do you get that info from as far as I know RTH does not turn OA off and I think you can set it to go around obstacles

Page 13~15 of the user manual, and does seem to be obstacle avoidance enabled for the Air 2S in return to home.

There's three kinds of RTH , Smart which is user initiated, Low battery, and Failsafe (signal loss for more than 6 seconds). There's two manners included in smart, being straight line and power saving.

It appears to primarily brake, and then reverse away and then ascends to clear an obstacle. It doesn't do the bypass method like when you would fly normally.


Tree branches of course are not always visible to the sensors, and during an event like low battery RTH, if there are a number of obstacles at the set RTH height, the battery may run out before it can clear them all.

It also seems that during either low battery or failsafe RTH, the drone will not actually land when it reaches the homepoint until the pilot confirms it.

"During Low Battery RTH and Failsafe RTH, the aircraft hovers at 0.5 m above the ground and waits for the pilot to confirm it is suitable to land. Pull down on the throttle for one second or use the auto landing slider in the app to land. Landing Protection activates and the aircraft performs the steps listed above."

 

[karlblessing]

This part seems important as it pertains to the OP's original question:

If the aircraft reaches the max altitude while it is ascending during RTH, the aircrafts stops and returns to home at the current altitude. If the aircraft reaches the max altitude while it is ascending after detecting obstacles in front, the aircraft will hover in place.

In this case, make sure your max altitude is set a bit above the RTH height (usually it's set to the legal maximum height you can fly).

To clarify with the OP, if RTH is set to 50, and trees are at 51 while it's moving forward. It'll stop, back up a bit, ascend a little until it can't detect an obstacle in front and continue forward. If the ascension happens to hit the max overall height set, it'll just hover in place.

 

[Ospreywatcher]

Best to cancel RTH as soon as possible after contact re-established then ascend to a higher position before pressing RTH again. I regularly cancel a RTH myself before resetting or doing a manual return and land.

 

[Ospreywatcher]

Best to cancel RTH as soon as possible after contact re-established then ascend to a higher position before pressing RTH again. I regularly cancel a RTH myself before resetting or doing a manual return and land.

 

[Yorkshire_Pud]

@hopeful21 really you should read the manual, page 15 to 17, there quite a bit of information in there and you really should know it or have at least a recollection of the basic behaviour that will happen.
DJI Mini 3 Pro - Downloads - DJI
oddly I don't see a French version listed.
or in English

https://dl.djicdn.com/downloads/DJI_Mini_3_Pro/UM/20221026/DJI_Mini_3_Pro_User_Manual_v1.4_en.pdf

A failsafe RTH has a number of behaviours that you may not know about including two entirely different RTH heights depending on just the distance from the home point, i.e. current height and RTH height.
"1. If the aircraft is 50 m or less than 50 m from the Home Point, it will fly back to the Home Point at its
current altitude"

But realistically I imagine that the circumstances where the current-height RTH will happen will be rather rare, unless you fly around the far side of something that is more or less right beside you.

So, I would say you should always look at your prospective flight path and, with the possibility of an RTH in mind, 'judge' the height of the highest obstacle that may lie in any RTH path and then add 10 or so metres to that height to get your RTH height.
You can always change an RTH height during a flight PROVIDING the drone is not actually executing an RTH. So if when you are getting near a possible obstacle you can always reassess the required RTH height and change it.

Secondly I would be wary of OA detecting bare tree branches and twigs, I wouldn't rely on it detecting them, if a tree is on a possible RTH path you want to be safely above it.

 

[LoudThunder]

I do not take off until the Fly App tells me the Home Point is Set. Since I am flying a Mini 2 with a Galaxy Tablet with the volume set on medium high, I actually hear the words…

I then lift off and perform some function checks, pitch, roll and yaw… and the App repeats the Home Point is set… I have set the Max height to 400' , even if there may be a lower ceiling (I do not want to accidently have the RTH restricted to 50' (ridiculous setting unless you are testing something…). I then ensure that the RTH height is set to a reasonable RTH altitude…

I have actually tested the RTH under all conditions so I know what to expect when the "unexpected" happens… I have set the RTH to 400' and I do not want to do that again… It's scary to see your drone take off and climb out of sight when you are not physically controlling it but trusting the app to bring your drone safely home. I had pointed the camera down and I kept switching between the camera view and the Map and it was little comfort until I heard the familiar Buzz of my little bird coming home…

DO NOT Take Off until your RC tells you the Home Point is Set, DO NOT Fly away until you have checked your Home Point on the Map and the RTH height is higher than all obstacles Trees, Towers, Buildings, etc…) in your flight area.

If you ignore this advice, do not be surprised when your drone flies into a tree or lands in a nearby pond…

I'm Done…

 

[hopeful21]

Well, thanks for that, all you good people. I have read the manual, of course, as it is a legal requirement, but I wanted to know what people's experience is. Practical is usually better than theoretical, but I didn't think that most pilots would have come across this problem. Where I was flying that day there is a max height of 50 metres, but when flying I found there were wooded areas that looked to be 60-70m. It was at that point that I lost signal. Fortunately the return journey was over woods that were <50m and, anyway, I was soon able to cancel the RTH.

I suppose one plan would be to set the max height to 60m anyway, but only fly at 50m, hoping that there will be no emergencies.

Thanks everyone for your input.

 

[Yorkshire_Pud]

A couple of things I would suggest,
1) An unneccessarily high RTH height is unwise. Assuming the drone has to climb to RTH height it wastes power in both the climb and the descent and, at somepoint, that may be critical.
Whilst it wasn't critical, I have experienced a too high RTH setting, way WAY too high, an accidental setting that went unnoticed until it was too late. It was during a disconnection RTH. It can take a loonngg time to get a drone down from height lol. Excess height may also put the drone up into high wind, (I was very lucky that day). With the Mini 3 this is not as great a concern as it was with the Mavic Mini but it is, arguably, not a good idea.

2) The RTH height can not exceed the maximum height, the App wont allow it. I experimented with this a while back.
If the maxiumum height limit is reduce to below the RTH height, the RTH height setting will be automatically reduced, by the App, to the maximum height setting. If the drone is above the new maximum height then the control system will reduce the drone's height to match the new maximum height setting.

You might like to have a look at DJI Wanda's post, no 6, in the thread A question for DJI. With drones that have obstacle avoidance that...

 

[karlblessing]

DO NOT Take Off until your RC tells you the Home Point is Set, DO NOT Fly away until you have checked your Home Point on the Map

Especially if you're taking off near a shore line, always fun to see your homepoint 20 feet off into the water and not noticing til it starts to come down if you're the type to rely on RTH for landing.

 

[Xitor]

First thing I do after hover test is fly to the highest object in the area I will be flying then set RTH at least 20 feet above that. For instance today, tallest items in area were 50 feet so I set RTH to 75. Plenty of clearance. Also not uncommon for news helicopter or air ambulance to go by a couple areas I fly in and those sure seem a bit lower than 400 feet.