Concentric coil for IDX

[dfbowers]

Well, since I have been asked several times about how to build a concentric coil for the IDX project I decided to collect some of the scattered details and put them together in a .pdf. Since I have already built several coils, I cannot take new pictures of every detail. I had to scrape together some older pics to illustrate construction methods. Happy reading! Don

[KahlesMilcon]

Cannot view PDF Link.Forum will not allow.

[dfbowers]

Cannot view PDF Link.Forum will not allow.

Try again. I had to repost the attachment. It's working now.

[ashefr10]

hi Don, I made a head with two D values that you gave me at earlier data. 27 cm. I will try soon is there something special to do because at the base idx must hold a concentric head.

[dfbowers]

hi Don, I made a head with two D values that you gave me at earlier data. 27 cm. I will try soon is there something special to do because at the base idx must hold a concentric head.

I just fill the "ears" on the coil with epoxy and fiberglass.

[Jerry]

I just fill the "ears" on the coil with epoxy and fiberglass.

I have been using epoxy and thin strips of scrap cloth. Anything to give some binder to the epoxy. Works well.

Jerry

[dfbowers]

I have been using epoxy and thin strips of scrap cloth. Anything to give some binder to the epoxy. Works well.

Jerry

One problem I ran into was getting the epoxy to stick to ABS plastic.. only the encapsulating compound that I have been buying sticks well. I just bought some plumbers epoxy made for plastics at a hardware store to try. I would lke to know what solutions others have come up with.. pvc primers? Sanding??

[golfnut]

One problem I ran into was getting the epoxy to stick to ABS plastic.. only the encapsulating compound that I have been buying sticks well. I just bought some plumbers epoxy made for plastics at a hardware store to try. I would lke to know what solutions others have come up with.. pvc primers? Sanding??

Could you use the potting compound as an adhesive - now that you know it sticks!

Steve

[dfbowers]

Could you use the potting compound as an adhesive - now that you know it sticks!

Steve

Yes, that is what I have been doing but it is expensive and has a limited shelf life so I usually reserve the whole 350ml for a complete DD coil.
I was just looking for a more economical solution.

Don

[Jerry]

One problem I ran into was getting the epoxy to stick to ABS plastic.. only the encapsulating compound that I have been buying sticks well. I just bought some plumbers epoxy made for plastics at a hardware store to try. I would lke to know what solutions others have come up with.. pvc primers? Sanding??

I have been using Loctite two part epoxy. http://www.loctiteproducts.com/p/13/...a-Time-Pro.htm

It is expensive but on the plus side it works well and is available any time I need some at a store that is located less than five minutes from the house. It is also very slow curing.

I do swab the inside of the shell with PVC cleaner and also use some 150 grit sand paper for those areas where I can reach. I also cut pieces of 1/4 inch paneling to shape to fill void spaces between the coils to cut down on the amount of epoxy I use. I glue these in place along with one of the coils before proceeding with the second coil and more pieces of wood.

I have not made anywhere near as many coils as you have so my experience is somewhat limited. However I have not had any problem at all with the epoxy filler separating from the plastic shell, or separation between first and second layers of epoxy.

Jerry

[dfbowers]

I finished some "garden variety" testing today on my latest 10" coil for the IDX project. Overall it was a successful project
Some notes on performance comparisons of 4 concentrics..

1. Performance of both 10" concentrics, one for the TGSL project and one for the IDX are for all practical purposes, identical.
The IDX coil wins in air tests by a long shot but the advantage is diminished in ground test. The TGSL 10" coil wins by 2 oz in the weight category.

2. Performance of both 7.5" concentrics, one for the TGSL project and one for the IDX. The IDX is the clear winner in the depth category.. almost matches the depth of the 10" coils.. but not quite. The 7.5" for the TGSL comes out ahead in the weight department (or lack thereof) and seems to have the cleanest discrimination.

Don.

[dfbowers]

Adding a short garden test video of the 10".
http://www.youtube.com/watch?v=u4XkOegLX-w
These are ½” lead balls buried at 1” increments.
Just for comparison, I did the same test with my Shadow X5.

http://www.youtube.com/watch?v=rvyNN7jsNGw

[golfnut]

Hi Don Im going to copy what you did with your depth test set up.

Im going to get some lead shot, best I can get are 0.49", these will be similar Im sure.

I need to clear all of the iron rubbish from my lawn.

Then we can get a like for like on the IDx's. Mine is a bit messed about with, like te Tx osc is direct from batt, and Tx coil/cap give 11.5Khz.

When I get the test bed complete I can test get a result, then modify idx, who knows it may already be as good as it gets.

I want to try to boost the geb channel as this is the sensitivity bottleneck - Iva an idea in mind for this.

Steve

[dfbowers]

Hi Don Im going to copy what you did with your depth test set up.

Im going to get some lead shot, best I can get are 0.49", these will be similar Im sure.

I need to clear all of the iron rubbish from my lawn.

Then we can get a like for like on the IDx's. Mine is a bit messed about with, like te Tx osc is direct from batt, and Tx coil/cap give 11.5Khz.

When I get the test bed complete I can test get a result, then modify idx, who knows it may already be as good as it gets.

I want to try to boost the geb channel as this is the sensitivity bottleneck - Iva an idea in mind for this.

Steve

Hi Steve.
Should be an interesting test. Sorry about the details. I actually used a .58 Cal bullet for my test. If nothing else, I will get some .50 caliber lead balls and repeat your tests, although we cannot duplicate ground types.

I am probably going to start a 2nd 10" coil this week as I sold the one I posted pictures of to another member. It should take me two or three evenings to put another one together.
On another note, I was messing around one evening and decided to see if I could get one of my coils to run at 15kHz. While it did work, it seemed more noisy than at 6.59k and the Tx waveform looked a bit strange, but it did work once I figured out the phasing.
Don

[golfnut]

Ok Don Ive prepared the test bed last night and today. Clearing the mass of iron was the hardest part as I didsnt want to ruin the grass ..

I took delivery of some shot balls and I think they are lead - they seem a bit light and a bit hard for pure lead? So maybe an alloy - unclear.

Anyways they are all the same diameter/age/material/shape. So I will get a good relative, repeatable test.

If anyone wants some to try pm me.


I started my first ball at 4", then every inch to 12"


I set my disc to reject Iron as I would normally, properly rejected. First ball at 4" came thru nice, second one at 5" was ok, next one at 6" I would have missed, all of the others too.


If I back the Disc off to let everything though I get the buried targets at 6" and 7" - So what I learned..

1)Its not as good as I had hoped - I dont get coins below 4" generally.
2)To get deeper I have to open up the Disc - the problem there is, you would be seeing all of the iron - so impractical - spend all of your life mining iron scrap.


So its all to play for my IDX is a bit ~ entry level', shall I say.

Got my tesoro 8" covers now, they are really rigid covers - 3mm thick good quality. 2 back to back would make a strong coil.

I will probably make a coil using one cover. Waiting for my grahite delivery, then need some cheap paint..

When completed I will re do the test on the bed and post. If still the same, the bottleneck is the IDX.

Then its either make a new machine or redesign my IDX.

Steve