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munroney

Metal detector sled

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I'm wanting to construct a sled to pull behind an atv. I don't necessarily care about deep seeking but rather expanding the width of the search (2-3m) As a newbie to the world of detectors, I don't want something that is just going to confuse me. I'm hoping to spend about $1000 if possible, maybe more if I have to, but I was hoping a fairly simple machine with a longer coil would work. I am aware that some metal detectors aren't compatible with longer coils so I was hoping you guys might know what would be best for me. Any help is much appreciated ?

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The Australian have been dragging coils around for years...you might look there...also, Doc was selling a thing for that...

fred

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I don't know a thing about these things, but it seems something like the hotfootrug is what you're after..

Swamp

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What detector are you thinking about using for this venture ? 

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From the sled aspect they can be very cheap and easy to construct as they are built with white schedule 40 pvc and glued together using pvc cement and primer which is really easy to use and assemble, these products can be purchased at any home improvement or plumbing store. 

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A rough plan for PVC Sled forgive for crude but suffice pvc parts list and diagram

IMAG0268~2.jpg

IMAG0269~2.jpg

Edited by Rocky

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A sled ? without snow ? ....I dont get it :idunno:

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   The largest coil I've ever seen someone build was 1 meter mono.  The things only have like two turns of wire.  Anything golf ball size and small is not going to be detected worth a poop.

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For larger surface areas and deeper objects you can build a large non metallic search coil structure out of PVC that acts exactly like a regular coil on a detector, that works with a detector with a extra long search coil wire, you can pull it behind a atv or car or anything else, heck you can carry or drag the sled if you really wanted to and have the tenacity. so instead of having a 10 inch search coil you can have a  6ftX6ft search coil, or whatever you can demand and I honestly have no idea of the limits.

53 minutes ago, adam said:

A sled ? without snow ? ....I dont get it :idunno:

Edited by Rocky
I eliminated ordinary from detector type because I don't know how ordinary of a detector it actually needs to function properly.

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1 minute ago, homefire said:

   The largest coil I've ever seen someone build was 1 meter mono.  The things only have like two turns of wire.  Anything golf ball size and small is not going to be detected worth a poop.

this type of coil is probably only sutible searching for large irons or palasites. So OP must be on a mission!!!

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 A normal PI timing would not function on coil that size.  Tx Power On times would come to play.  Other timing issues too.  You may get away with like a Lorenz.   Or a Modified Deepers, XR-71.  

 

 

Edited by homefire
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I have designed and built metal detector electronics for my own use but never made a large coil detector.

The first issue is whether to use a VLF continuous wave, or Pulse Induction (PI) design.

Most systems like this use a PI design because the coil is just a simple loop.(mono coil). VLF systems that drive the coil continuously,  need a design where the net magnetic flux into the receive part of the coil is carefully nulled to zero within about one part per million by careful mechanical design. This usually takes the form of a double D where the loop is a figure 8 with overlapping section in the center, a concentric coil where a big transmit loop has a small reversed coil in the middle, or a design where the transmit  coil is horizontal, and the receive coil is vertical. In all cases, the strong transmit flux is approximately zero at the sensitive receive coil. In addition, there is an LC circuit added to further null out any residual flux due to phase changes.

Any mechanical flexing of a large coil mechanically nulled like this would disturb the nulling and give a false signal.

So unless you want to just line up a bunch of VLF detector coils, probably the PI approach is better.

No coil nulling is needed for PI since the large transmit pulse flux is finished when the sensitive receive section is on and the system listens for signals from the target's induced eddy currents.

If you already have a PI system, you might just be able to swap in a larger loop of similar inductance. ( Larger area, fewer loops).

 

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Since you are not interested in depth, you don't need a large (e.g. 6'x6') coil, but can make a wide and narrow coil like 6'x1'.

This should still give you about a 1' depth, be more sensitive to smaller targets (than a 6'x6' coil), and better match the inductance of the normal mono coil.

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Hi,

What kind of meteorite are you looking for chondrite or iron meteorite.I would use a Pulse detector for Iron meteorites.We have tried to build a drag for chondrites and nothing really works. I have a drag that I have built and found numerous Iron meteorites. You can see my meteorite drag on nevadameteorites.com . I have a Lorenze detector and 4'-12' drag for sale with 2meter coil and a 1 meter coil set up for ATV or tractor.

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Coils that size have issues your basic PI circuits not going to deal with so well. 

 

1.  Energizing the coil would require a longer Tx Pulse ON Time.  A single Fet like IRF9640 would most likely get too toasty give up the Magic Smoke.

2.  Longer Feed Line cause more parasitic capacitance taking longer for the Fly Back to settle down.  Some Serious Damping and Longer Sample Delay could fix.

3.  Larger Coil presents more cross section to act as a Antenna for EMI, RFI and Ground Noise ( Capacitance ) .  Most commercial PI detectors are not equipped with the Front End Filtering that would be required. 

4.  Anyone attempting to plug a coil like that into a MineLab , TDI or the Like is in for a expensive learning curve.

 

If this was my project I think I would employ a TWO BOX TR detector set up. 

 

 

 

If they only knew about PI technology in WWII !  They almost got there.  They used Magnetic Fields to Detonate Magnetic Mines with a set up almost right. 

 

 

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On 7/17/2017 at 8:26 PM, munroney said:

I'm wanting to construct a sled to pull behind an atv. I don't necessarily care about deep seeking but rather expanding the width of the search (2-3m) As a newbie to the world of detectors, I don't want something that is just going to confuse me. I'm hoping to spend about $1000 if possible, maybe more if I have to, but I was hoping a fairly simple machine with a longer coil would work. I am aware that some metal detectors aren't compatible with longer coils so I was hoping you guys might know what would be best for me. Any help is much appreciated ?

Coiltek makes a 20 x 40 coil  ....And you can have my SD2200V2 Control box for 500.00 even 

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Thanks for the reply’s everyone, that was a lot of good info to take in. I had no clue that chondrites would be difficult to detect with a wider coil. The hotfoot rug sounds interesting (and I’d definitely like to eventually try it) but I think I might just stick to a regular detector for now. I went shopping the other day and tested out a Whites GMT, M6 and a Garrett AT GOLD, and the winner seemed to be the AT GOLD. I have never heard of this machine being used for meteorites and was wondering if anyone has any feedback on it for this purpose.  The ground balancing was incredible and managed to discriminate between a 100g hot rock and a 5g ordinary chondrites. Any info would great 👍

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May I ask how you checked out these detectors? 

One thing you have to keep in mind is different detectors will produce different results in different soil conditions for different types and sizes of meteorites. 

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On 2017-11-19 at 5:18 AM, Morlock said:

May I ask how you checked out these detectors? 

One thing you have to keep in mind is different detectors will produce different results in different soil conditions for different types and sizes of meteorites. 

Good point. I was only able to wave some ordinary chondrites infront as the detector was tilted up. I just learned that having the detector on an angle may give inaccurate readings but I was told If it can detect in air then the results will be even better in the ground

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I have to ask, as a fellow Canuckistanian, where abouts in Canada do you plan to detect where you have such wide flat smooth surface that you can use a blanket or huge tow behind coil? Are you east of the Rockies?

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I’m from near Vancouver but I’ll be heading over seas to some flatter/drier ground. Might take a shot at the new bc meteorite in the spring tho 😉

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I know what he’s talking about! There was a TV show about two meteorite hunters in KS, that pulled a PI coil on a sled behind an ATV. Not sure if the coil was home-built or purchased.

Can you put a PI 1M x1M on a pvc platform sled, like the diagram??

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55 minutes ago, rrtdave said:

I know what he’s talking about! There was a TV show about two meteorite hunters in KS, that pulled a PI coil on a sled behind an ATV. Not sure if the coil was home-built or purchased.

Can you put a PI 1M x1M on a pvc platform sled, like the diagram??

I believe they used a Lorenz PI type sled searching for the Brenham pallisite. They had lots of success with it. 

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