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Comment by declan_roberts | Hacker News Reader

I was trying to figure out exactly how it charges with just 1 pole. It must be induction in that case, right?

From the video description:

> A passively actuated gripping mechanism grasps the powerline cable during landing after which a control circuit regulates the magnetic field inside a split-core current transformer to provide sufficient holding force as well as battery recharging.

When the grippers close they probably close the loops of a coil that wraps around the wire. So it's harvesting the ever changing magnetic field that arises from AC current, independent of voltage. You can still get some power from coils that aren't wrapped around the wire but are still parallel. I think that's how wireless phone chargers work.

You can also take power using a capacitor instead of an inductor, from the changing voltage (not current) in an AC line. Like when you hold a florescent tube vertical under a hi-power line, and it lights up.

That is induction though. Acapacitor alone can not extract energy from a ac line. Inductance is what allows energy transfer here.

It could have a small spool of wire to drop to the ground to make contact. This would allow the drone to rest on the wire while charging.

This would vaporize the drone, the wire, and anyone or anything nearby, sending flaming battery and electronics shrapnel in many directions. High tension does not mess around.

See what happens to a branch:

https://www.youtube.com/watch?v=g4ph-h7l_aM

Or a conductor hauled up by fishing line

https://youtu.be/mqRT7J86rco?si=Za9B-dA-VO-Fl5Z8

Not if you put a large enough resistor in the line. It might be enough just to extend a spike to bleed off charge, though.

There's nothing gentle about 38kV. You're not going to lower down a line and bleed off some charge. Once there's a viable path to ground, current will flow all over whatever is making that path, including the very air around it. The entire drone, wire, and the air it is inside of will turn into vaporized plasma as if hit by a bolt of lightning. And 38kV is low voltage in the high-tension world.

Creating current flows from a field is what induction is, so if you're imagining that you could just generate electricity from a field, well, that's what they're already doing. It doesn't take lowering a probe. You can just use an inductor.

That is exactly opposite of what would keep the drone safe. In a power transmission network the earth is a conductive path. Touching a phase and touching earth allows the grid to push as much power through you as your impedance and grpund contact will allow.

That, and long spools of loose wire and spinning propellers are not a good combination.

The link below is a video showing the explosion that would occur if someone attempted what you are describing.

https://youtu.be/LCRfYIwFbxQ

If it can make contact with the ground it should be able to charge from the static field.

https://makezine.com/article/craft/1000-fluorescent-lights-p...

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