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Making A Drag Coil From Scratch


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Big idea from a bloke with no idea!!!  Hoping that this forum can be of some assistance 🙂 

Well, with another trip to Western Australia done and dusted my last statement to my brother in law before I left was that "I don't think I will be back without a drag coil".  Aaaaaaaand I am hoping to go back next year  🤣

We did OK considering we were genuinely 'prospecting' and we knew that it may be a boom or bust type situation.  

The issue is that we passed over so much country because it is just too big.  Vast.  Expansive.  And much of that vastness looks exactly the same - where the hell do you start? 

And of the patches we did find, then gridding out from those located pieces would be far more efficient and easier on the body than the side-to-side, slowly moving forward, small step action that gridding requires. 

I'll proceed with what I want to do, what I don't want to use, what I hope I can build and then questions re: what is actually feasible.   I have looked through a few topics on here and there are snippets that can be picked up but not specifics and the cans, cants and have to's and how to's.  I am really hoping to build a thread that anyone can follow and build their own basic coil design or at least have the basic idea of where to start.   I'm hoping that @Reg Wilson @Chet @jrbeatty @Aureous @jasong @Geotech and others with technical expertise and prior experience can be helpful. 

Disclaimer - image.png.e5ebb170431188bbf8e2526082bc8ff5.png 

 

 I checked out Geotech forum and although I am sure it is a fantastic forum I am sorry to say that it is all just too far over my head.  I really need things in laymen's terms.  I guess it is a case of if you never learnt it you just don't know it and I don't have the time to go and do a diploma in electronics.  I help student/new nurses go through a step-by-step-by-step process of changing vacuum dressings on huge abdo wounds or changing PICC dressings or setting up a syringe driver for a palliative care patient.  They are technical things and they need guidance, unfortunately I am asking for the same guidance here  🙏  

 

My basic plan - to make a 5 or 6 foot wide, oval or rectangle shape, mono coil that I can drag myself - not with a vehicle of any sort.  My goal is coverage more than depth although depth is always a welcome advantage I suppose.  I would be hoping such a coil could pick up shallow gold pieces that are 2 grams and up??  

Mount the windings inside plastic tubing (inch poly??), solidify those windings inside the tubing with either some sort of foam or resin, affix that to the top of a folded piece of non-metal conveyor belt, place a solid timber on the front edge/folded edge of the belt and tow with a rope.  All connected to a GPX series (4000/4500/5000) detector that can be carried on a harness with the battery, etc.  

As I am trying to keep-it-simple-stupid I am hoping that the windings can simply be bundle wound and that a gel type resin will both provide some weight, some rigidity and keep the windings in place.  

I do not want to use a vehicle due to the extra cost of purchasing a vehicle, transporting it and the EMI complications it can bring.  

As I will be pulling the device it needs to be reasonably light weight but not so light weight that it is not durable and that it does not remain as flat as possible.  

I know there is a pre-fab ready-to-go option with an @Coiltek 40 inch drag coil but I am wanting something a little wider to really make the process efficient.  And I might learn something along the way  👨‍🎓

So before getting into the what I need and how to do it, I really need to start with 'Is it possible?'.  

Noting Reg's post below re: as things get bigger they develop more problems - is a 72 inch wide coil even feasible?  Is this why Coiltek don't make anything over 40"?  

The build itself it adaptable but I am guessing the physics is not, so that is the first hurdle I need to over come.  

 

Question 1 - Will physics defeat me before I even start? 

 

Look forward to your responses 🙂 

Cheers, N.E.   

 

 

On 5/11/2023 at 9:02 PM, Reg Wilson said:

A problem with drag coils is that the bigger you build the more that the problem develops, being that the ground balance varies from one side of the coil to the other. 

Unless you have a detector that can handle such electronic variations and still give accurate readings you will find 'sledding' (drag coils) challenging.

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I have found a few new ground patches, but in most of them only one or two nuggets would of been found with a drag coil and even less with the size that you desire, the rest you need to grid by hand. How ever you can cover a lot of ground with a machine dragged coil in shorter time in poor ground. I'm sure other will give you their opinions of what is worthwhile, best of luck. 

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  • The title was changed to Making A Drag Coil From Scratch

I've helped a couple of mates build a drag coil. Issues that arise are:

Getting the coil windings to the correct spec when dealing with large sizes.

Getting the shielding values correct.

Allowing for a longer than normal lead (which alters said specs).

Getting the ideal size calculated due to the GPX's ground tracking ability not keeping up with large coils (as Reg has said). 

Finding the ideal matting material to mount the coil to and bonding it well enuff to stay on for the duration.

When dealing with these issues, it becomes quickly apparent  that they are always towed from a quad bike or larger vehicle due to the weight of the coil and mat. The lightest one I've ever seen was about 8 kilos. The heavy rubber matting is required to sustain wear from dragging (which is multiple times more abrasive than swinging). Mounting the coil to your body and dragging will never be a comfy option. One fellow I knew even used an old Postie bike to some effect so ya dont need any large vehicle. 

So, when taking into account the fact that you need a vehicle and THAT requires the electrics of that vehicle to be nullified, you are left with an AI design. This design assists with the ground balance effect also. But a bit of sensitivity is lost.

Best option for ground coverage Ive ever seen is to get a 24" elliptical mono and train yourself to efficiently swing at a brisk walking pace. The 30x7 NF patch mono is also a great option.

Geof is correct in that a lot of great patches are missed due to the lack of sensitivity in drag coils. This is something that the large ellip monos mentioned above are great at.

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I've never built or run one myself. I hope I can meet up with Chet again sometime and check one of his out or maybe give it a go in person and learn a bit more. Until then I can't really comment with much useful.

I definitely relate to the "big country" issue though. It can be an overwhelming amount of land to cover. Barring a better solution, the only ways to tackle it for me have come down to 3 things basically: speeding up by using a lightweight, quiet, fast detector (I've posted about this technique a ton, but it's not for everyone granted). Geologic/topographic indicators. And using an ATV to speed up movement between low probability zones, as well as to do a lot of scouting by eye first.

I'd say at least 50% of my field prospecting in big country now is standing on my ATV while driving and just looking at the ground with my eyes, or getting from the most likely place to the next most likely quick without walking or detecting in between. I'm missing a lot, but I'm also usually only spending time detecting in the most probable spots when there is just too much ground to feasibly detect.

I'd love for there to be a better solution...starting to look unlikely we'll get one though. 

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One very good suggestion that Ive heard for massive ground coverage is..... <wait for it>.... Buy a QED and mount one of the affore-mentioned large ellip mono's onto it. They are the lightest PI detector out there and if you buy one for the single intention of chasing patches with one coil, its a killer outfit. No need to change the settings of the detector, just set it up once (for the one task) and use it that way always. Cheap, lightweight and ya can swing it all day long.....

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Like many others I'm sure, it's something that I put some thought into 45years ago, I was working in plastic fabrication at the time, my brother in law was an electronics wiz, I though of something with wheels and a tow line attached to a winch. I had in mind the large number of areas in W.A. that are flat, including salt lakes. Thinking about it was as far as I got. It's interesting to hear that the idea still has merit, good luck with it N/E, I hope you can make it happen, in fact I think you can.

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Thanks everyone for the comments so far and a bit of a reality check - I always knew in the back of my mind that it would not be as straight forward as I hoped  😉

 

3 hours ago, Aureous said:

hey are always towed from a quad bike or larger vehicle due to the weight of the coil and mat.

3 hours ago, Aureous said:

Getting the coil windings to the correct spec when dealing with large sizes.

Getting the shielding values correct.

Thanks Aureous - yes, the shielding will be another hurdle.   

Re: a tow vehicle - I am pretty steadfast on the need to pull this myself, for a couple of reasons.   

The first is cost - both the purchase cost, and the cost of a trailer to put a motorbike in and then the extra cost of towing, etc.  All of that is simply not an option for me for what is essentially a hobby.  If I lived in the W.A. goldfields then it would be a different scenario.   

The second is that in W.A at present there is a bit of a push from the pastoral lease holders requesting prospectors to not use combustion engine motor bikes (2 wheel or 4 wheel).  Apparently having a lot of issues with cattle.  The 3 different stations we went on this year all requested the same thing.   My brother-in-law is a member of APLA and we very much try to do the right thing and follow requests, whether they 'legally' need to be followed or not.   It hopefully means no issues for us returning in the future and we also don't need to provide any further ammunition for pastoral lease holders/mining companies to further their efforts to reduce prospector access.   

I'm a big lad and quite fit so dragging something that moves reasonably easy over the ground (even at 10 kg) should not be too hard of an ask. Although I may get some carpet, a 10 kg weight and give that a whirl before I make too many claims   😁

 

2 hours ago, Aureous said:

Buy a QED

Yeah, naaa, thanks anyway   🤣

 

A 40" X 20" Coiltek may end up being the resultant purchase but I'll tease this out as far as I practically can  👍

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You might have better luck building a unit that can be mounted to a drone. There are used commercial drone that would handle about 25 pounds, and that should be enough to handle the coils and detector that can send information to your phone.

Granted it would not get most targets very deep, but if they were large ones it will show you where to dig.

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What about towing it around behind an E-bike?

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21 minutes ago, phrunt said:

What about towing it around behind an E-bike?

Yes, we did talk about e-bikes.  My B-I-L bought one of these ( see link below) about 8 months ago as APLA has their own recommendations that you don't drive your 4X4 everywhere on a tenement - I'm not really sure why.  They encouraged the use of a 4 or 2 wheel motor bike.  Now pastoralists do not want that.  

https://fatcatbikes.com.au/

Again, initial cost of a decent e-bike, carrying it around, length of time you would get out a battery, possible EMI interactions - I'm really just happy to drag the thing  😊

 

Have also just seen these  -  https://detectormods.com/shop/77/flexible-drag-coil   

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