When NOT to trust your app.

[Former Member]

Some people are really dependent on technology, almost to the point of letting it override common sense. Sometimes I check Accuweather before leaving the house. If Accuweather says it's raining outside, I go and look out the window to see if it really is or not. They are right about half the time. So if they say 50% chance of showers, and they are right half the time, I reduce that to 25% chance of showers. Works for me.

Drones use technology and they are not always right. The Mavic has so many sensors, that if any one of them is not calibrated to what its supposed to be doing, it can lead to a fault or crash. Also, dont always rely on technology to save your bacon. Some examples are the downward sensors not being able to accurately detect water. Others might be the inability of the obstacle avoidance to detect a tree branch, obstacle avoidance not working at night, and counting on return to home to get you out of a bind.

You need to use common sense to protect your investment. If something doesnt seem right, despite what the app says, it probably isnt.

That being said, a good way to protect yourself and your drone is to use prop guards in tight spaces, be careful over water, do NOT rely on the batteries internal voltmeter to accurately measure the batteries level especially when going down to the nether regions of below 20%. I liken that to riding an older motorcycle with fuel gauge. I wouldnt depend on it once it drops below half.

A word to the wise is sufficient, but for a fool not even a stick helps...

Best regards,

Rob "Benjamin Franklin" Schwartz

 

[tleedom]

Words of wisdom to fly by.

 

[Former Member]

Words of wisdom to fly by.

As a helo pilot, you know what I mean!

 

[Afremont]

To be pedantic, the downward facing ultrasonic sensors have no trouble "seeing" water. Its just that the flight controller makes the assumption that it's a solid surface.

 

[Former Member]

To be pedantic, the downward facing ultrasonic sensors have no trouble "seeing" water. Its just that the flight controller makes the assumption that it's a solid surface.

Youre not pedantic, youre right.

 

[tleedom]

Back in the day, I was never really comfortable trusting anything I couldn't see. That usually meant Wx forecasts from young Air Force Wx forecasters.

 

[Former Member]

To be pedantic, the downward facing ultrasonic sensors have no trouble "seeing" water. Its just that the flight controller makes the assumption that it's a solid surface.

Would you mind explaining how the downward sensors work and what they "see" when it comes to water?

 

[RickMz]

Back in the day, I was never really comfortable trusting anything I couldn't see. That usually meant Wx forecasts from young Air Force Wx forecasters.

Not like the old AF Wx (certainly not the 8AF ones) forecasters where much more accurate, they just could hedge better!!! LOL

 

[dronerdave]

... do NOT rely on the batteries internal voltmeter to accurately measure the batteries level especially when going down to the nether regions of below 20%. I liken that to riding an older motorcycle with fuel gauge. I wouldnt depend on it once it drops below half.

A word to the wise is sufficient, but for a fool not even a stick helps...

At least my bikes have always had the reserve fuel supply valve. But I see what you mean and over critical areas & I do limit my battery reserves to above 30% for my flights.

 

[Former Member]

At least my bikes have always had the reserve fuel supply valve. But I see what you mean and over critical areas & I do limit my battery reserves to above 30% for my flights.

Thats funny and youre right! The first real motorcycle I ever rode I borrowed from my friend when I was 10 and it didnt even have a fuel gauge. I rode it till it ran out of gas. Ended up pushing it 2 miles to a gas station. Told the story to my friend. He asked why I didnt turn the reserve lever, to which I replied, "whats a reserve lever?"

 

[dronerdave]

Thats funny and youre right! The first real motorcycle I ever rode I borrowed from my friend when I was 10 and it didnt even have a fuel gauge. I rode it till it ran out of gas. Ended up pushing it 2 miles to a gas station. Told the story to my friend. He asked why I didnt turn the reserve lever, to which I replied, "whats a reserve lever?"

What really sucks is when the reserve runs out!

 

[Former Member]

What really sucks is when the reserve runs out!

Oh I would never let that happen. (is my nose growing yet?)

 

[BD0G]

One of the more common things that is overlooked is Magnetic Interference. Pilots rely upon the Mavic to know accurately which way it is pointed when in point of fact it can be 180 degree's off. They routinely dismiss the Mag Interference message when it is no longer on the Remote Controllers screen.

Mistake!

The quick way to check that the orientation is correct and corresponds with the compass is to look at the Radar Display and see if it indicates that the Mavic is pointed in the direction that you can physically see when looking at the Mavic.
If you point the Mavic away from you , but the Radar display has the Red Arrow pointed back towards you. Well then there is an issue. That issue is entirely related to Magnetic Interference.

This is another example where pilots need to physically inspect the Mavics orientation and not trust the compass and sensors to always be correct.

 

[Meta4]

do NOT rely on the batteries internal voltmeter to accurately measure the batteries level especially when going down to the nether regions of below 20%.

You probably mean don't trust the battery % indicator.
The voltmeter is able to be trusted, but you have to enable the display of battery voltage level to see it.

 

[Former Member]

You probably mean don't trust the battery % indicator.
The voltmeter is able to be trusted, but you have to enable the display of battery voltage level to see it.

Actually, I did mean the voltmeter built in to the internal circuitry of the battery which is represented by the voltage display on DJI Go 4. I would not trust it to give me accurate remaining time on the flight or voltage when it gets down to or below 20% because thats when many Lipos tend to dump.

Another related issue about running the battery lower than 20%. The battery at a displayed remaining capacity of 20% has used 80% of its energy. Thats fine, as long as you know what your cell balance is at that low of a percentage. If the battery gets down to 20% or lower, you dont really know what is making up that 20% unless you have the battery window open. Cell 1 could be 25%, cell 2 10%, cell 3 could be 25% for an average reading of 20% between the 3 cells which is what the battery % display shows. Cell 2 will dump alot faster than the other 2, and when that happens, the battery will drastically disharge faster than it did during the first half of the discharge cycle or flight. This will tend to happen on older batteries, in extreme weather conditions, and when the battery is under stress. The weak cell will try to keep pace with the 2 stronger ones, and drain faster making the situation worse, and possibly into the critical zone.

A good example of the above is letting the battery run that low when you are far away. When you hit the RTH button, or when the drone determines that it's time to head home on its own, the drone will try its best to get back home with the power it has left. If it is reading from the internal voltmeter, it doesnt monitor individual cell voltage, but voltage as a whole. If you have one bad cell, it's 90° outside, and the drone is fighting a headwind coming back, it very well might not make it back.

I try to stick to my 40% rule. Im usually on the ground when it gets down to 40, and there are very few surprises. Batteries tend to last longer that way too.

 

[brett8883]

Actually, I did mean the voltmeter built in to the internal circuitry of the battery which is represented by the voltage display on DJI Go 4. I would not trust it to give me accurate remaining time on the flight or voltage when it gets down to or below 20% because thats when many Lipos tend to dump.

I think what @Meta4 means is that a digital voltmeter is an incredibly reliable and accurate device. It’s gonna display the correct voltage of the battery. But I think what you are saying is the conversion of remaining voltage to remaining flight time is what can’t be trusted.

 

[Former Member]

I think what @Meta4 means is that a digital voltmeter is an incredibly reliable and accurate device. It’s gonna display the correct voltage of the battery. But I think what you are saying is the conversion of remaining voltage to remaining flight time is what can’t be trusted.

Thanks for the explanation.

The digital % display on the DJI Go 4 display main screen might be accurate but it's not not reliable. Even the remaining flight time might be accurate but not reliable. A truly reliable and accurate Lipo voltmeter will give you an individual display of each cells voltage. You can only get that by opening the battery window. Most pilots dont need individual battery cell displays because the batteries tend to be built very well, and a new battery will mostly discharge evenly. But sport mode pilots, and pilots who fly in extreme conditions might consider keeping the battery cell voltage window open to prevent damage to the battery, especially when going below 30%.

Probably most important is the pilot who is trying to RTH. Yes the voltage % might be 20%, but if one cell is in the red, game over very soon, despite what the % meter shows.

 

[brett8883]

Thanks for the explanation.

The digital % display on the DJI Go 4 display main screen might be accurate but it's not not reliable. Even the remaining flight time might be accurate but not reliable. A truly reliable and accurate Lipo voltmeter will give you an individual display of each cells voltage. You can only get that by opening the battery window. Most pilots dont need individual battery cell displays because the batteries tend to be built very well, and a new battery will mostly discharge evenly. But sport mode pilots, and pilots who fly in extreme conditions might consider keeping the battery cell voltage window open to prevent damage to the battery, especially when going below 30%.

Probably most important is the pilot who is trying to RTH. Yes the voltage % might be 20%, but if one cell is in the red, game over very soon, despite what the % meter shows.

I don’t mean the % indicator because even that is making an assumption about the amount of flight time remaining compared to the amount of time that has already expired. I’m talking about the actual display of voltage like 3.68 in @Meta4 ’s example which is the voltage of the cell with the least voltage of the all the cells. So I can tell that all of @Meta4 ’s cells have AT LEAST 3.68 volts left without having to look at the battery window.

I get your point though about making sure you get home with plenty of time to spare. But you aren’t saying there’s a problem with the volts that are being displayed in the app correct?

 

[Meta4]

The digital % display on the DJI Go 4 display main screen might be accurate but it's not not reliable.

The % indication can give horribly false readings if the battery is not fully charged before a flight.
But the voltage display is accurate and gives a proper indication of what's in the battery.

 

[old man mavic]

i have to agree that it is easy to put to much trust in the automated systems built into our UAVs such as the sensors on the drone the display info etc,this is why i have always advocated,learning to fly your drone manually until the control becomes second nature then if problems arise during a flight you are better able to get your pride and joy back safely,there is nothing wrong with using the technology but you need an understanding of the limitations, that can effect the ability of the drone to operate safely in unexpected situations, and end up crashing or getting lost