Neutral Buoyancy Coil

[hobbes_lives]

I am building a coil for a PI, and am using the Hays Electronics 11" O.D. open search coil housing. I am looking for suggestions on the best way to make the coil neutrally buoyant in salt water. You get extra points if the coil still remains relatively lightweight.

[ApBerg]

Only the most necessary parts in epoxy ( cable connection and coil ), then for the part were is air make some holes in the coil so that water can run in and out….
For the rod connection I had the lower part connected inside the coil housing.
This makes the resistant ( moving ) in the water must lower ! ( for the extra points …)
Look at the form.pdf.

Ap

[amtech2005]

Neutral Buoyancy Coil

ApBerg , It looks like the jigs/forms are made of wood , very inexpensive !!! Are these search coils permanent and solid , can you hit or tap the search-coil on the ground with no changes to windings/signal - HOW STABLE IS IT ?????...............Thanks................Eugene

[ApBerg]

Hello Eugene.

Yes this is low budget coil making that works very well ! At the Newbury really in 1985 we get to know John, he made his own coils and was so kind to tell the secret’s about it !
Somebody now’s John ? Every year we send Christmas cards….not last year…

Use for the coil ABS , a ‘plastic’ that we al know, it is used for al sorts electronic stuff :
TV/ Pc’s/ Printers/ Car dashboards etc. If you heat it in a oven it gets weak so you can press it in a form, I use a cheap pizza oven….. first on the oven-bottom a extra metal sheet for better heat regulating.
As glue you can use acetone in a glass bottle , put some little ABS parts in it and leave it for a day, shake as now and then. It has to be so thick as cold oil.
As wood for the form you can use MDF from 18 mm – 22 mm, MDF is easy to work with. The part you cut away is used as press, so the saw you use to make the form has to be a little thicker than ABS you use…The ABS needs the cut away space to fit in…
I have made coils that are used more than 10 year … so no problem to make your own coils this way.
As you can see for sear sing in water I made a coil that is inside the sears coil connected, the cable finds his way in the rod so it gives no resistant in the water……

Be careful with Acetone, be careful with Tools ! the saw you see in the PDF doc. Is for illustration only !!!

Regards.

Ap

[ApBerg]

Forgot :

………. to make the coil ‘solid’ I use 2 components foam, the same as used in surfboards.
Do not use the 1 component foam ! it will stay elastic. The 2 components is hard in 1 hour.

ABS is not UV resisted, you can give it a paint spray to prevent that it gets cracky (?)


Regards.

Ap

[hobbes_lives]

ApBerg, that's pretty cool how you make your own coil housings. Good work!


I'm sure most of you are familiar with the Hays coil housings, but for reference, the housing that I am using is "A" on the following page...
http://www.hayselectronics.com/parts.htm

The coil I've wound is a monocoil and mostly fills up the outer ring. That leaves the center section hollow, which will be really buoyant if filled with foam or air. I think filling it with epoxy would work, but it may add quite a bit of weight too.

[amtech2005]

Neutral Buoyancy Coil

I was wondering if anyone has tried this product for a search coil sealant ???? And does this product have any electrical characteristics , that may have a negative effect . It is spray foam I have used for plumbing insulation , but I do not have a can at the moment . I am not trying to sell or endorse this product !!! But , it is just an idea for quick search-coil making . .....Any ideas on this , or a similar hard drying Foam ????.............Eugene

[homefire]

Great Stuff is OPEN CELL type foam. No Water Proof.

[amtech2005]

Neutral Buoyancy Coil

Thanks Homefire , If it is not waterproof then we will scratch it off the list , or use "Great Stuff" as primary , and have a secondary type paint or coating that is waterproof. I am sure there is something similar on the market that is waterproof . But ApBerg has found a good system to set a coil . And I am sure others will post on this subject also.........Thanks......Eugene

[hobbes_lives]

I just wanted to point this out, in case anyone decides to try and go down the same path I did.

I tried using "Great Stuff" to fill a void area inside a coil enclosure. I drilled a hole in the enclosure and sprayed "Great Stuff" deep into the void using the tube that is supplied with the product. It foamed out of the hole, and the overflow dried to a nice firm consistency.

I figured all went well, until I removed the foam covering the hole. The foam inside the housing did not expand and dry like the foam that came out of the hole did. It is now just a gooey mess inside the housing, not hard foam at all. I guess I'm going to hope it eventually dries and just leave it as is, with a big void.

Hopefully this warning will save someone from the same frustration that I have right now.

[ApBerg]

Hello Hobbes,

Tray to find 2 component PU foam (polyurethane) it is a closed cel structere foam that after 1:1 mix expands its by volume 25x. You need very little to mix for a coil , the time you can work with it is ca 2 minutes ! it is hard after ca 60 minutes .

Succes.

Ap

[Roughwater]

Great coil making

AP,

Awesome coil housings. I have bought some Hayes coil housings and yours look just as good.

Terry