Extendable/retractable Telescopic shaft/rod

[TJPMusic]

TL;DR Summary

What are some methods for engineering an extendable/retractable telescopic rod about the dimensions of a car antenna?

Hello all. My first post here. Thanks for having me.

I’m working on an electrical prototype which has a couple of odd requirements.

The device uses a 3’ high voltage continuous arc to perform its intended task.

In order to start this arc without using a crazy amount of voltage, I’m going to implement an arc ignition procedure— basically starting the conductor at a point very close to the return path, and then extending it out to its full length— this should enable me to achieve said arc using only about 12KV.

The challenge? How to do it...?

A motorized car antenna seems like a good start, but: the nylon cable idea is not going to be strong enough- and, I need the conductor to extend very quickly.

Should I be looking at modifying an existing “rod”, say, a car antenna, or trying to fabricate something new? My skills are mostly electrical, not so much mechanical.

One idea I had was to use some sort of worm gear or auger to extend the rod quickly, but the nature of a telescopic rod basically prohibits that, as far as I can tell.

Please school me- I am terribly naive in the mechanical world.

Any help is greatly, greatly appreciated— thanks!

 

[berkeman]

Welcome to the PF.

I am terribly naive in the mechanical world

I hope you are a lot less naive in the high-voltage electrical world!

Can you spring-load the telescoping pole to ensure that it extends quickly? It looks like there are lots of versions available...

 

[TJPMusic]

Thanks for the quick reply!

And yes, don’t worry, I’m a boss with an HV probe and a hack with a ratchet. Lol

That’s certainly a possibility, my issue with that method is going to be the thickness and strength of the shaft, and whether it can hold up to its intended abuse, which will be high in the final product. Not so much in the prototype, I just need to show that the prototype works.

Retracted, the shaft should be about 6” to 1’ in length to fit the design profile. Max thickness at base of the shaft couldn’t exceed about an inch, hopefully skinnier, about a half inch, if that’s possible!

Also, does there exist such a spring that’s so powerful but so skinny?

 

[TJPMusic]

Worth mentioning, “quick” extension means within about a second, not anything crazy quick. Just faster than your Honda Accord antenna... lol

 

[Dr.D]

Would a Jacob's Ladder do?

 

[TJPMusic]

Are you talking about an electrical Jacobs ladder? Or something mechanical? An electrical Jacobs ladder is actually pretty dissimilar to what my prototype is, though it does use a large arc.

Similarly, though, it does require the arc to start close to the return path at the bottom, and then extend the length while maintaining the pulsed arc.

 

[Dr.D]

I was simply asking if the electrical Jacob's Ladder might do the job.

 

[berkeman]

That’s certainly a possibility, my issue with that method is going to be the thickness and strength of the shaft, and whether it can hold up to its intended abuse, which will be high in the final product.

Can the shaft extend in a downward direction instead of upward? If so, you could use a weighted end to be sure it extends downward quickly...

 

[TJPMusic]

In this application, seconds would count- and it would need to deploy no matter what at the press of a button. I really like the spring loaded idea, actually- I am just unsure where to look for such parts hardware store? Any suggestions for finding bits and bobs and springs online?

 

[256bits]

In this application, seconds would count- and it would need to deploy no matter what at the press of a button. I really like the spring loaded idea, actually- I am just unsure where to look for such parts hardware store? Any suggestions for finding bits and bobs and springs online?

What about one of those "shock absorber" units you see on car trunks.
They are spring loaded and extend at a predetermined rate.

 

[Baluncore]

It would be wise to analyse the operating arc and surrounding electric fields due to the upper electrode, conductor support and withdrawn striking structure. What supports the upper electrode?

What maintenance current will flow once the arc is established? DC or AC? Negative Earth?

Long candle flames become unstable in a few inches. Will the buoyant 36 inch high column of arc ionised gas accelerate upwards sufficiently to become unstable?
For how long is the arc expected to operate as a stable vertical column?

How will you reduce UV radiation, and ozone release at the top of the arc column?
How will you reduce EMI radiation from the loop antenna = HV generator + conductor circuit + completed by the arc.

This is a bit like a Poulsen arc transmitter. Will you have an alcohol fuelled flame at the base to generate ions?

 

[TJPMusic]

@Baluncore
Wow, you honestly just presented 4 or 5 different points I hadn’t even considered— thank you! I have to think about these things.

I have been hesitant to reveal too much of the design, but you folks are obviously more educated than I am, and you seem very willing to help out.

Anybody familiar with the ring magnet arc experiment to create a Plasma Vortex?

Essentially, the flux lines around a ring magnet will Guide an arc from a conductor placed in the center of the ring into a perfect circle around the inside of the magnet.

I propose this same phenomenon can be enlarged/extended to become a useful, long stream of plasma around a strong central conductor. There are lots of questions. I know that the air is going to create a lot of variables. My idea is that once the arc is started, the plasma channel will have enough negative resistance that it will require only a reasonable voltage (around 12KV rather than 100x that for the arc to jump the air gap on its own), thus enabling more current for a stronger plasma bolt, and making the device a little bit less dangerous for rogue arcing... (It should be noted here and now that every experiment AND the final product will be battery powered and FULLY ISOLATED from mains/Earth, and as of now the experiment is limited to 240W.)

I really don’t know what’s going to happen once I get to the full length. Early experiments have been VERY promising. But we’re talking 6 inch to 1 foot long arcs, using a wand to start the arc, rather than a telescopic center conductor. Now I just need to SAFELY make it bigger. Though, the end device IS designed to be a self-defensive “tool”.

I really just do not know what’s going to happen at 3 feet. And whether or not it’s going to even be safe to be even close to the thing outside a Faraday cage, let alone to hold one in your hand ... if anybody has figured out what I’m trying to build yet, don’t say it out loud... Lol

 

[TJPMusic]

@Baluncore
Would you suggest a pulsed DC or a resonant/reactive secondary using AC? Which method would make for a hotter bolt of plasma? I would assume DC... Sorry Nikola

 

[TJPMusic]

What about one of those "shock absorber" units you see on car trunks.
They are spring loaded and extend at a predetermined rate.
View attachment 255443

Great idea! I’m not sure how I could implement that into this design, but certainly worth the thought! It would definitely have to be a neutral/non-flammable gas inside the strut...

 

[Baluncore]

Would you suggest a pulsed DC or a resonant/reactive secondary using AC? Which method would make for a hotter bolt of plasma?

With a permanent magnet guide, DC will have one flow pattern, with AC there will be fluttering between two patterns.
AC will not “stretch” as far as DC, because it will extinguish during the change.

 

[DaveE]

Any suggestions for finding bits and bobs and springs online?

There are about a million places. I like https://www.mcmaster.com/ but amazon and ebay work pretty well too.

 

[anorlunda]

Temporarily closed for moderation.

 

[berkeman]

Summary:: What are some methods for engineering an extendable/retractable telescopic rod about the dimensions of a car antenna?

The device uses a 3’ high voltage continuous arc to perform its intended task.

Now I just need to SAFELY make it bigger. Though, the end device IS designed to be a self-defensive “tool”.

This doesn't sound like something we should be helping you to design and build. Thread will remain closed.