How do you calculate RTH time quickly?

[giovi321]

Hi everyone,
how do you manage your return to home time based on the battery range remaining? Is there a faster way than calculating (roughly, and in my head) if the 5 minutes left of battery are enough to go back to home for 5km? Obviously I do the math, but is there a faster way?

 

[Yorkshire_Pud]

You do not need to, DJI drones do it for you and initiate a low battery RTH when they calculate it is needed.
Read the drone's manual, the relevant section is probably called "low battery RTH" or similar.

Since you do not mention a model I will add, I think some give you a running countdown which also varies with the distance so, whilst it continual counts down, the time remaining may increase if you bring the drone closer.

If you cancel the low battery RTH you may not get another warning until the drone starts a forced descent.
All this is likely covered in the drone's manual.

Some people do chose to cancel this RTH but it's at their peril and quite a few drones have been lost because of this, their subequently saying "but I have done that many times before and got away with it" gets little sympathy.

I am not sure if it takes wind into account but then I know not to fly downwind to distance, which means the return home is up wind.

 

[FLDave]

To determine RTH capabilities you need to thoroughly understand current conditions:
1. What is the wind where the drone is flying? What is the wind at different altitudes and geographic locations within the RTH route.
2. How much battery remains and what is the current battery usage rate?
3. What obstructions are on the RTH route?
4. How is the drone visibility reacting to current conditions.
Or, just DJI do the calculations for you and you manage the VLOS conditions.

 

[giovi321]

Yes I didn't know that DJI app does it automatically. I usually do it when I sail (by motor), so the calculation is fairly easy to me I'm used to it (also considering wind).

 

[Felix le Chat]

You do not need to, DJI drones do it for you and initiate a low battery RTH when they calculate it is needed.
Read the drone's manual, the relevant section is probably called "low battery RTH" or similar.

Since you do not mention a model I will add, I think some give you a running countdown which also varies with the distance so, whilst it continual counts down, the time remaining may increase if you bring the drone closer.

If you cancel the low battery RTH you may not get another warning until the drone starts a forced descent.
All this is likely covered in the drone's manual.

Some people do chose to cancel this RTH but it's at their peril and quite a few drones have been lost because of this, their subequently saying "but I have done that many times before and got away with it" gets little sympathy.

I am not sure if it takes wind into account but then I know not to fly downwind to distance, which means the return home is up wind.

The thing I much prefer with the older GO4 app is the 'time remaining' readout on the top power bar. The little white pill shows flight minutes left which varies according to how hard the motors are having to work (headwind/shear etc.). Gives you a much more realistic and accurate estimate. One reason among many I don't particularly like the dumbed-down FLY app.

 

[Yorkshire_Pud]

Yes I didn't know that DJI app does it automatically. I usually do it when I sail (by motor), so the calculation is fairly easy to me I'm used to it (also considering wind).

Ahhh in that case you MUST do things somewhat differently and reset the home point at reasonable intervals.
The home point is a fixed point of the earth's surface, since the boat moves away from that point the drone WILL NOT RTH to the boat but will RTH to open water.
Regular updating of the home point to the controller's location will give the drone a better basis for its calculations.
Not being nasty, but I think you should spend some time reading the manual and this forum, you are 'looking' at flying from a moving platform and that is likely to entail hand launching the drone from the stern and WILL almost certainly ENTAIL hand catching the drone and "flipping it" to stop the motors.

 

[Droning on and on...]

I'll check later, but I swear Fly gives you estimated remaining flying time before low-battery RTH will automatically kick in, next to the battery circle that is the same as what GO4 indicates with the bar.

This is based on safe return to home. That's why it decreases as you get farther away from the Home Point.

 

[giovi321]

I'll check later, but I swear Fly gives you estimated remaining flying time before low-battery RTH will automatically kick in, next to the battery circle that is the same as what GO4 indicates with the bar.

This is based on safe return to home. That's why it decreases as you get farther away from the Home Point.

Aaaah I thought that it was the time remaining before the battery dies! Makes much more sense now, that's why the number changes so often, obviously as the drone goes further or closer the time changes

 

[Yorkshire_Pud]

Aaaah I thought that it was the time remaining before the battery dies! Makes much more sense now, that's why the number changes so often, obviously as the drone goes further or closer the time changes

Did you see post 6 ?

 

[giovi321]

Did you see post 6 ?

Yep , fortunately I was already aware of this!

 

[giovi321]

Ahhh in that case you MUST do things somewhat differently and reset the home point at reasonable intervals.
The home point is a fixed point of the earth's surface, since the boat moves away from that point the drone WILL NOT RTH to the boat but will RTH to open water.
Regular updating of the home point to the controller's location will give the drone a better basis for its calculations.
Not being nasty, but I think you should spend some time reading the manual and this forum, you are 'looking' at flying from a moving platform and that is likely to entail hand launching the drone from the stern and WILL almost certainly ENTAIL hand catching the drone and "flipping it" to stop the motors.

I meant to say that I do this calculation FOR the boat when sailing using the motor. You need to make sure that you can get back otherwise you're stranded at sea

 

[Yorkshire_Pud]

I meant to say that I do this calculation FOR the boat when sailing using the motor. You need to make sure that you can get back otherwise you're stranded at sea

Uum, just a point, the information you see in the app is based on the most recent home point so the distance ( drone to home point ) quickly loses relevance when compared to the distance to safety ( boat ).
I am not nit-picking, just trying to ensure your drone is safe and doesn't go swimming.

 

[DARKSeifer]

If you set the distance in meters and the speed in meters per second you'll get the easiest math around.

Unless it's windy, and you flew with the wind on your back you can trust the battery indicator, if you return home the first time it prompts to return you'll always have enough juice to get home.

And in general, if you are flying VLOS, you shouldn't care at all about remaining battery. Because real VLOS, where you can clearly see the attitude of the drone, is about 150-250 meters at most, and you can fly that distance in just 10 seconds. No one flies drones VLOS btw, they just pretend that a dot at 400+ m is VLOS.

 

[giovi321]

Thanks to all of you for the super help!

 

[Droning on and on...]

Uum, just a point, the information you see in the app is based on the most recent home point so the distance ( drone to home point ) quickly loses relevance when compared to the distance to safety ( boat ).
I am not nit-picking, just trying to ensure your drone is safe and doesn't go swimming.

An alternative is to deliberately set the HP on shore in a safe place so that if anything goes wrong chances are good you'll be okay.

I don't know about the rest of you, but this is how I've done it the few times I've been in a boat. Trying to remember to constantly update the HP to my location while I'm focusing on flying and filming is too much of a workload for me.

Remember you can set the HP to a location on the map.

 

[MS Coast]

Aaaah I thought that it was the time remaining before the battery dies! Makes much more sense now, that's why the number changes so often, obviously as the drone goes further or closer the time changes

The estimate of remaining flight time varies with more than just distance to the home point. Flight speed, rate of climb, camera use, ...