Comment by K0balt

5 days ago

Mmmmmmmmmmhhh. Maybe better to damage A battery than to have a drone fall out of the sky? Also most protected cells have modest current capabilities, and might not be enough for many drone applications.

By its nature, MUAVs tend to push batteries to their limits and lifecycles tend to be limited. A battery that does mission X must have a maximum weight and a minimum capacity, and a minimum current spec. If you increase the life cycles, you decrease the maximum performance (range, payload, etc).

When you get into bigger drones, more modest restrictions on mission capability give acceptable tradeoffs, but for MUAVs short cycle life is often seen as an acceptable cost.

Frequently , after a hundred (or often much less) cycles in a MUAV a battery is retired from stressful missions due to significant drops in capability. It’s still fine for other uses, but at 90% it’s no longer sufficient for frontier MUAV applications.

The best choice to keep drones from falling out of the sky is to make sure that your auto land is set to a reasonable battery level (calibration by height if you will be at altitude) and use cell cutoffs at or below the minimum safe voltage if at all. (They are usually set to a few tenths of a volt above the minimum safe, often as much as 500mV.) The final battery voltage should be managed manually and batteries tested if over-discharged.

At least, that’s what prevents the most hardware from falling out of the sky onto people’s heads, sometimes bursting into flame on impact. Usually that is seen as the least desirable outcomes of a battery stress situation.

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K0balt

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walrus01  5 days ago

So I was referring specifically to this phone hardware project and to flashlights, which don't fly... But my thoughts on drones are also that it's very different if you're building consumer class things that are meant to be re-used or what's going on in ukraine right now. They're using high amp rate cylidrical 18650 and 21700 cells in 6S2P and 6S3P packs for one way trip munition drones where you don't particularly care if you damage the li ion cells for any future re-use. In which case in the last few minutes of flight you can abuse the hell out of them with high amperage draw down to 2.5V (but beware of extreme voltage sag at the bottom end) and never have to worry.

If we're talking about something that's designed to be re-used then a totally different set of design considerations, as you outline above, become applicable.

> Frequently , after a hundred (or often much less) cycles in a MUAV a battery is retired from stressful missions

Are you talking about lipo pouch cells or li-ion cylindrical? Because if we're talking about state of the art high amp draw rated li ion cylindrical cells, 100 cycles on something that isn't heavily abused for heat and doesn't go below 15% state of charge should not significantly affect its lifespan. But if the batteries are being abused or every last bit of margin on range/payload is needed that it calls for almost "factory fresh" cells, or there's just absurd amounts of DoD money to throw at buying new battery packs, sure, I guess.

  • K0balt  5 days ago

    If you’re getting into bigger (kg+) drones, it starts to make sense to shoot for 100cycle+ (and for 10kg+, 1000 cycle-ish) lifespans. The economics and the physics work out. But for very tiny systems like the single cell drone featured, the equation starts to favor squeezing every last drop of energy reasonably possible, which means that you can easily get caught out downwind or “stayed to get a few too many pictures” and end up hitting the safety walls. (Partly because the risk of doing so is proportional to the size)

  • K0balt  5 days ago

    Oh that’s hilarious.

    I got this article conflated with another I was reading. My apologies to all.

ssl-3  5 days ago

What are the chances of this telephone falling out of the sky due to battery failure?

  • K0balt  5 days ago

    I was going to say pretty low but then I realized you weren’t just be ing snarky lol

    I got this article conflated with another I was reading. My apologies to all.

    Still, if you don’t want your phone to fall out of the sky, Put it on a drone with proper battery limit discipline.

    • ssl-3  4 days ago

      It is interesting to note that Kobalt 24v power tool batteries don't have any internal over-discharge protection. I guess this can make them better-suited for flying telephone use than some alternatives.

      ;)