Basic question: battery swaps?

manutter51 · Mar 16, 2022

Just flew my first thermal imaging mission for DroneBase, and I had a question about battery swaps. I've got a DJI M2EA, and I programmed the mission in the Pilot app, and it went pretty well. The assignment was to scan the roof of a commercial building and I just about made it on a single battery. In fact, I did make it, except that I had a little extra margin all the way around, and I didn't get the last couple of rows. What happened was the battery began to get low, the beeping started, and I let it continue to fly until it hit the "I want to go home" point, at which point it said it was going to return to home in 8 seconds, and I just clicked OK to have it return immediately. A few messages flashed on the screen briefly (one of them being "Aircraft in the area"), and then I think it said it was cancelling/terminating the mission and returning to home.

I was expecting Pilot to automatically suspend the mission and return to home for a battery swap, but apparently I was expecting too much? It definitely terminated the mission once I clicked OK on the return-to-home dialog, so there was no "Resume" button or anything for me to pick up those last couple strips. Fortunately, I allowed a generous margin all around, so I think I'm good as-is. But I have another mission coming up this weekend, so I'd like to know exactly how battery swapping is supposed to work. Am I supposed to hit the Pause button on screen and manually fly it back for a swap? If I do, and then hit Resume, will it automatically pick up where it left off?

R.Perry · Mar 17, 2022

This is just my opinion. First of all you shouldn't ever let your batteries get that low. On a large mapping I will pause the flight and RTH when my batteries hit 30% unless the mission is very close to being completed, I never go below 20%.
Two reasons, the deeper the discharge on a battery the more heat is creates. Secondly if your drone does not make it back before the batteries go dead your drone crashes. One of the jobs I had required four battery changes, probably could have done it on three but I look at battery power for what it is, the fuel that keeps my drone flying. I'll spend the extra time to be safe, and I believe it is better for the batteries.
I use the Drone Deploy mapping software and it will continue the flight from where it ended for a battery change.

manutter51 · Mar 17, 2022

Thanks, yeah, I wasn't happy about letting my batteries get that low, I just wasn't sure if that was how Pilot normally handled swaps. I've got another mission this Sunday, I'll definitely hit the pause and bring it in manually this time.

BigAl07 · Mar 17, 2022

I totally concur with @R.Perry
.

I don't have an aircraft that utilized DJI FLY so I can't comment on how it behaves but DD handles battery swaps with ease.

manutter51 · Mar 17, 2022

Does Drone Deploy automatically fly back for swaps, or do you have to manually pause and resume?

R.Perry · Mar 17, 2022

No, Drone deploy RTH is initialized by hitting the RTH icon on your DD app. It will give you low battery warnings.

jaja6009 · Mar 17, 2022

Some points to consider.

Know your aircraft inside and out. Do not learn about it as you fly it especially for a paying client.

The proper workflow is to hit Pause, then fly it back manually or use RTH.

Swap your battery and either continue from the ground, or launch and then continue.

Please make sure you are familiar with your aircraft and all features such as RTH, Geofencing and exactly how all modes of Pilot work.

It would be a real shame to lose $6500

manutter51 · Mar 18, 2022

jaja6009 said:
Some points to consider.

Know your aircraft inside and out. Do not learn about it as you fly it especially for a paying client.

The proper workflow is to hit Pause, then fly it back manually or use RTH.

Swap your battery and either continue from the ground, or launch and then continue.

Please make sure you are familiar with your aircraft and all features such as RTH, Geofencing and exactly how all modes of Pilot work.

It would be a real shame to lose $6500

Oh absolutely. I'm at the point now where the problem is thinking that I have the knowledge I need, only to discover unsuspected gaps in my knowledge. Thanks for the detailed response.

Ajkm · Mar 19, 2022

It may be worth Googling the discharge graph of the batteries we use, as it’s not exactly intuitive to understand. There is a fairly steep drop to the cells nominal voltage, followed by a steady discharge. However what then happens is what catches pilots out: there is an extremely rapid drop off for the last 20% or so.

In other words, the discharge of a battery is not linear. If you fly down to 20% and try your luck further, you may well run out of power entirely. That is why experienced pilots will swap batteries around 25-30% remaining.

manutter51 · Mar 19, 2022

Ajkm said:
It may be worth Googling the discharge graph of the batteries we use, as it’s not exactly intuitive to understand. There is a fairly steep drop to the cells nominal voltage, followed by a steady discharge. However what then happens is what catches pilots out: there is an extremely rapid drop off for the last 20% or so.

In other words, the discharge of a battery is not linear. If you fly down to 20% and try your luck further, you may well run out of power entirely. That is why experienced pilots will swap batteries around 25-30% remaining.

Good to know, thanks!

R.Perry · Mar 19, 2022

It is my opinion that by only running your batteries down to no lower than 20% you will extend the live of the battery due to the fact that the batter heat will increase much faster below 20%, and it is my understanding that excessive heat will kill Litho batteries.