Making A Drag Coil From Scratch

[cobill]

On 5/15/2023 at 6:20 PM, GotAU? said:

How about pulling the 40x20 CT Mothership coil sideways on a little PVC pipe cart or sled?

@Northeast I'm also contemplating a cart/sled setup for deeper gold in flat areas. Here is a pic of one of Doc's designs using an SD 2100, according to Trevor @Coiltek the older ML analog SD & GP units work best with large coils. What did you decide?

Bill

[Northeast]

On 10/15/2023 at 1:24 AM, cobill said:

What did you decide?

Hi Bill, 

When I came back from W.A. I was all gung-ho about making one for myself, thinking that it would not be all that hard.  Wrong!  At least, wrong for someone with not a great deal of electronics know-how. 

I was very lucky that one of the Prospecting Australia members got in touch with me and over several emails essentially provided all of the info re: what I would need to make an Anti-Interference coil about 4 and a half feet wide.  He even kindly offered to assist with the final calibrations of the coil after I had got it to a certain point.  And I still owe him a slab of beer or some wine for his troubles!  However, I had none of the required materials and to purchase it all from scratch was going to cost more than I was prepared to fork out considering I wasn't actually sure that I wasn't going to stuff it up!  

About that time a barely used Coiltek 40" wide AI coil became available at a very low price and I thought I would dip my toe in the water with this as a starting point.  

@Jonathan Porter also advised that those coils worked better on the SD/GP models so I ended up getting a GP3500 off @PhaseTech that he had just traded back in - and actually was one of his own personal units he had previously sold.

I set up my test skid arrangement with a piece of heavy duty, folded lino (flooring material) and also set up a bit of a test bed with some different sized fishing sinkers.  

I had a lot of trouble finding any real settings online for running the big AI coil with a GP3500 so tried lots of different things and was actually a bit underwhelmed by the depth the coil achieved, especially on a quite large, solid, round sinker at just less than a foot deep.  However, I was amazed that my GPX6000 also did not pick up this particular piece so perhaps it had something to do with that.  I cannot remember the settings I ended up thinking were the best as this was a couple of months ago. 

I also might have access to a GPX5000 soon and hope to give that a trial and see if different settings might actually improve things re: depth or if the newer models indeed do not run any better (or maybe worse).  

I will take a photo of my little skid set-up when I get home tonight.  It is very light, easily dragged by me and simplistically effective in moving over sticks and rocks, etc. 

The lino was purely to see if the design will work.  I am now trying to source a piece of polycarbonate to use in place of the lino as it will be far more abrasion resistant and I think even lighter.  Bunnings (a home hardware store in Australia) have just what I need only it is not wide enough. It is only 1 metre wide which is only just the width of the coil.  I would like an extra 4 inches either side of the coil just to provide some protection.   I may just have to forego the extra width and use this in the end though.

https://www.bunnings.com.au/suntuf-5-x-1m-x-0-8mm-clear-uv2-polycarbonate-sheet-handi-roll_p1010854 

For a multitude of reasons the last few months have seen little prospecting for me.  The next few months that should change and I hope to get much of this sorted ASAP as I have just put in for 7 weeks leave next year to enable a 'proper' trip to Western Australia!

Cheers, N.E.  

[cobill]

8 hours ago, Northeast said:

I had a lot of trouble finding any real settings online for running the big AI coil with a GP3500 so tried lots of different things and was actually a bit underwhelmed by the depth the coil achieved, especially on a quite large, solid, round sinker at just less than a foot deep. 

@Northeast Thanks for your detailed reply, not much info is available online & I also found a WA post that said "the AI coil must be run in DD mode and there was a massive loss of sensitivity and depth".  Maybe better to try Woody's www.detectormods.com  concept, can change layouts, save some frustration, time and money:

Bill

[Northeast]

5 hours ago, cobill said:

Maybe better to try Woody's www.detectormods.com

When I get some more time on the current set up and if I’m not completely happy I might then explore the Woody’s loops.  At first glance they looked like exactly what I was after but I’m guessing ground noise and EMI will be more of a concern with them but I also think sensitivity and depth will be much better.

I may contact Woody and see if he would allow a ‘try before you buy’ type thing.   He likes doing YouTube vids so maybe we could run both versions over a test bed and compare 🤷‍♂️

This is how I set up the Coiltek.  It looks basic and it is!! But it drags very easily, very flat and very close to the ground  

 

[Reg Wilson]

I think you will find that the lino setup will soon wear out on the highly abrasive ground in WA. I suggest you get in touch with Jason Cornish who is the Central Vic president of the PMAV. I loaned him my sled some time back, and he may be able to give you some advice based on his experience.

From my trip to WA with the sled I found that the GPX4000 was the detector of choice for the job.

[Aureous]

@Northeast if you ever need more advice on home building it yourself, just PM me. As you may recall, I've built 5  of these. Conveyor belt mat is the best option....as Reg says, the lino will abrade to shreds in no time. I have all the wire, shielding, inductance and resistance specs at hand. SD2200 may just be the best option. A folded mono AI coil will need to be run in mono mode, not DD. The Coiltek 'Zulu' or 'Mothership' coils are wound as a DD though.

[Northeast]

2 hours ago, Reg Wilson said:

I think you will find that the lino setup will soon wear out on the highly abrasive ground in WA

Yep, the lino set-up was just to see if the principal worked.  The second incarnation is to be polycarbonate which I think should be much tougher.  

 

2 hours ago, Aureous said:

Conveyor belt mat is the best option

I will try polycarbonate first as it will be much lighter than conveyor belt.  

 

2 hours ago, Aureous said:

if you ever need more advice on home building it yourself, just PM me

Thanks, I appreciate that  😉

[Reg Wilson]

DD coils are pretty useless for sledding as the target response is far too slow. Jim Stewart found this out the hard way in WA.

[Chet]

Coiltek sold three models of the Mother Ship coil; Mono, DD Pro and a Salt / AI coil. Maybe I missed it but I didn’t notice which model you have. Each model will respond the best in the environment that it was designed for.

In perfect ground with no EMI a Mono coil will beat the DD and the AI coils.

A round lead test target will return less signal strength than an irregular shaped nugget of smaller size and weight. Try chopping up and pounding out some large irregular shaped pieces of lead and plant them in the ground as a test patch to drag your coil over.

In my opinion you have a better more stable coil than a Do-It-Yourself coil.

[Drellim]

Wow I really like the way it is protected with  the sheeting   I have herd the SD was better with those larger coils a lot to watch out for  interesting indeed   How you pay attention  to all the sounds and manage that coil  that’s a lot going on But hey you are going for the big  one  best of luck