Low Battery Decending P-mode vs Sport?

[Kate]

being thoroughly human, i found myself at high alititude the other day and
there must have been a vertical wind, updraft? whatever it wasn't coming down as quick as usual
and i needed to get down before my battery went out.
bear in mind im reasonably cautious here and battery dead 'fall from sky' is %5-10 for me.

in any case, I suppose my question is:
When descending with a low battery; would you favor P-mode with a longer time to ground,
or use sport mode, using more juice, but getting down faster

I imagine the difference is negligible given potential energy and all that jazz, but i would be interested
to know others experience.

 

[AlanTheBeast]

being thoroughly human, i found myself at high alititude the other day and
there must have been a vertical wind, updraft? whatever it wasn't coming down as quick as usual
and i needed to get down before my battery went out.
bear in mind im reasonably cautious here and battery dead 'fall from sky' is %5-10 for me.

in any case, I suppose my question is:
When descending with a low battery; would you favor P-mode with a longer time to ground,
or use sport mode, using more juice, but getting down faster

I imagine the difference is negligible given potential energy and all that jazz, but i would be interested
to know others experience.

I don't think that matters as much as how far away you are from the drone. I'm pretty conservative with my return reserve and rarely land with less than 15%.

If the approach is clear you get a lot of range and vertical descent combining the two. In descent, the drone uses less energy so might as well move forward and down smartly.

From various sources the optimal range in no wind seems to be 50 km/hr. That's Sport mode or P-mode with OA disabled. (Landing is not the best time to disable OA in many cases, obviously).

IAC getting down fast with the down lever pinned seems really fast to me. That said, since the drone needs more energy to hover than it needs in forward flight, then the least energy descent is pin down the down lever and move forward at some good speed (15 - 20 km/hr) and that will conserve a lot of battery during the descent.

Be careful!

 

[Kate]

I will thanks.
This is strictly (mode 2) left stick descending. Drone above the RTH.
If descending on a course, then yup I would be moving forward, using the altitude as you say

 

[Cyberpower678]

I don't think that matters as much as how far away you are from the drone. I'm pretty conservative with my return reserve and rarely land with less than 15%.

If the approach is clear you get a lot of range and vertical descent combining the two. In descent, the drone uses less energy so might as well move forward and down smartly.

From various sources the optimal range in no wind seems to be 50 km/hr. That's Sport mode or P-mode with OA disabled. (Landing is not the best time to disable OA in many cases, obviously).

IAC getting down fast with the down lever pinned seems really fast to me. That said, since the drone needs more energy to hover than it needs in forward flight, then the least energy descent is pin down the down lever and move forward at some good speed (15 - 20 km/hr) and that will conserve a lot of battery during the descent.

Be careful!

If you switch to sport mode, the drone descends faster. With that being said to descend the drone reduces power to the motors to descend, so in sport mode, even more power is reduced, so moving forward while descending may actually use more power.

 

[CyberNate]

being thoroughly human, i found myself at high alititude the other day and
there must have been a vertical wind, updraft? whatever it wasn't coming down as quick as usual
and i needed to get down before my battery went out.
bear in mind im reasonably cautious here and battery dead 'fall from sky' is %5-10 for me.

in any case, I suppose my question is:
When descending with a low battery; would you favor P-mode with a longer time to ground,
or use sport mode, using more juice, but getting down faster

I imagine the difference is negligible given potential energy and all that jazz, but i would be interested
to know others experience.

I'm not sure that sport mode descent is any faster than P mode. I think they are both 3m/s. If the Mavic battery gets to 10% and lower, the rate of descent is doubled at over 6m/s. DJI does this for the obvious reason of getting the craft down before the battery dies.

At 6m/s, that's nearly 20 feet per second descent speed. That should be plenty fast to get the craft down. Lets say you're at 2000 feet. The craft would reach the ground in 100 seconds. 10 percent battery should be good for nearly 3 minutes of descending. Basically, you wouldn't want to be higher than 3000 feet when the battery reaches 10% worst case scenario.

 

[AlanTheBeast]

If you switch to sport mode, the drone descends faster. With that being said to descend the drone reduces power to the motors to descend, so in sport mode, even more power is reduced, so moving forward while descending may actually use more power.

The best descent speed to save energy will be the speed = endurance speed. Moving forward is required for that since endurance is not at hover.

DJI paint the endurance as 25 km/hr - that can be done in sport mode or P mode.

I checked the spec and whoever said max descent is 3 m/s is correct - I got that wrong.

The notion, of course of going at 51 km/hr is simply to get home quickest on remaining power (max range speed or damned close (51 km/hr pinned in P-mode with OA off)) - bear in mind that you may want to switch OA back on before landing - which is awkward to do.

So pick your poison according to distance and how much altitude you need to lose - when you're going down it's a certain thing that you're using less power than while maintaining altitude.

 

[Kate]

IIf the Mavic battery gets to 10% and lower, the rate of descent is doubled at over 6m/s. DJI does this for the obvious reason of getting the craft down before the battery dies.

really, wow. missed that one in the manual.


one thing i was pondering last night was if mavic does indeed shut down at %0 battery?
From what ive read in other threads, %0 is actually about %15-20 battery per the 80 20 lipo rule.

 

[AlanTheBeast]

I'm not sure that sport mode descent is any faster than P mode. I think they are both 3m/s. If the Mavic battery gets to 10% and lower, the rate of descent is doubled at over 6m/s. DJI does this for the obvious reason of getting the craft down before the battery dies.

At 6m/s, that's nearly 20 feet per second descent speed. That should be plenty fast to get the craft down. Lets say you're at 2000 feet. The craft would reach the ground in 100 seconds. 10 percent battery should be good for nearly 3 minutes of descending. Basically, you wouldn't want to be higher than 3000 feet when the battery reaches 10% worst case scenario.

I can't find mention of the 6 m/s descent rate in the manual. What page is that on (or what other reference do you have?).

You shouldn't be at 3000 feet in any case as the drone is limited to 500 m (1640 feet).

 

[CyberNate]

really, wow. missed that one in the manual.


one thing i was pondering last night was if mavic does indeed shut down at %0 battery?
From what ive read in other threads, %0 is actually about %15-20 battery per the 80 20 lipo rule.

I haven't verified this myself. I heard this from one of the videos where a guy was doing max range testing. I haven't found this documented either. I was trying to find the link and can't remember which one it was. If I find it, I'll update this thread. According to him, at a critical battery level it descents at a higher rate. I will test this the next time I get a low battery. I normally don't like to run my batteries down much below 20%.

Regarding the battery 80 20 rule, I don't believe they are that conservative with the battery. That was my calculation if the cells were 3200MAh. The battery cells are Lithium Polymer and I haven't been able to find the specs of their cells to know the real capacity. The one tear down I saw has an out of focus picture of the cells.

Regarding the maximum altitude, that is from take off point. If you are flying from high ground over lower areas it could happen that you are more than 2000 feet above ground at the time of an emergency landing. Here in the California Bay Area near the foothills the terrain is rolling. But yes, you are right. I wasn't even considering the maximum altitude settings. I was just calculating if there's enough battery to make it to the ground from various heights.

 

[cardplayer71]

Just watch that you don't lose lift and stall in your own prop wash. Circle down or descend in a "halfway home, halfway down" kind of way. I don't like vertical descent.

 

[CyberNate]

Most likely my statement regarding increase descending rate with low battery is incorrect. I cannot find a single mention of it for any of the DJI products. You can't always believe what you hear on youtube videos. Anyway, from an altitude of 500m, you should still be able to reach the ground at 3m/s before the battery runs out. The craft will start descending on it's own at the critical battery setting.

500m divided by 3m/s is 166.67 seconds. Descending takes less energy, so I'd expect 10% to last over 3 minutes with constant descent. On a video that I saw which tested the Mavic with a low battery, I saw 3.65V/cell at 11% reading. That is not very low considering the Nominal voltage is 3.7V. There should be at least 30% left at 3.65V. I'm not sure anyone has testing if the Mavic cuts power suddenly at 0%, or if 1% lingers for a long period of time.

 

[GreatScott]

Most likely my statement regarding increase descending rate with low battery is incorrect. I cannot find a single mention of it for any of the DJI products. You can't always believe what you hear on youtube videos. Anyway, from an altitude of 500m, you should still be able to reach the ground at 3m/s before the battery runs out. The craft will start descending on it's own at the critical battery setting.

500m divided by 3m/s is 166.67 seconds. Descending takes less energy, so I'd expect 10% to last over 3 minutes with constant descent. On a video that I saw which tested the Mavic with a low battery, I saw 3.65V/cell at 11% reading. That is not very low considering the Nominal voltage is 3.7V. There should be at least 30% left at 3.65V. I'm not sure anyone has testing if the Mavic cuts power suddenly at 0%, or if 1% lingers for a long period of time.

A o this is a good question. I think you can decend faster in this case with a tiny bit of corkscrew. Maybe because you are flying it down and it doesnot ha e to stabilize in its Prop wash etc?

This made me wonder if anyone else had done this in a case where you are descending for a reason aka fast.

 

[AlanTheBeast]

Just watch that you don't lose lift and stall in your own prop wash. Circle down or descend in a "halfway home, halfway down" kind of way. I don't like vertical descent.

I've yet to see a report of downward flight stalling - RVS - with a MP.

Also, if there is any wind, then a vertical descent wrt the ground would be quite safe.

(I prefer a forward descent as well if there is lots of room to do so).