DIY Bigfoot coil?

[multieagle]

Amazing how loose the central crossover wires appear/

[Polymer]

Thanks for posting the x-ray pics!

The guts of the Bigfoot looks quite complex and I can't make all to much sense of it for now.

You have inspired me to do the following:

I will travelling by air in Europe in the next weeks and will take my Bigfoot along with me for one purpose:

To get photos of it on the monitor when being scanned at the airport. They do have color enhanced x-rays at security
and it's amazing what they can see. I will ask nicely and it is paid for by all of us after all . So it shouldn't be a problem.

Wish me luck and I will post on my experience with this when I get back in 2 weeks.

[Davor]

X-rays reveal that Rx is wound as real figure 8. No surprise it was expensive to make. You may achieve the same effect by following no less than 3 approaches. You may successively wind figure 8 after figure 8 like Whites did, and no way you'd ever automate that. Second is to wind a large loop and twist it to form a figure 8 - it works the same as the current orientation is the same in the inner pass. The third method is to wind two loops of the same circumference and the same number of turns, join them in the middle to form a centre pass, and carefully pick the correct wires to connect to obtain the same current orientation in a centre pass. As for automation, the 3rd method would work the best. I have no idea why Whites did not go for that one.

As for phases, this concept is superb if you have a 4 quadrant Rx where phase reversal is irrelevant. The detection maximum is at the centre pass where there is double the wires than in the rest of the Rx coil. Double the wires with same orientation means double the voltage. As this nexus of wires is concentrated in a coil middle, this configuration must be very sharp for pinpointing even the smallest of objects. This is one of the reasons I wish to have a 4 quadrant rig with this very configuration of coil.

The other bonus is its immunity to EMC of any kind.

[Carl-NC]

White's never made the Bigfoot, it was a fellow named Jim Karbowski. He made them all by hand. When he died, a nearly defunct Discovery Electronics (Treasure Baron & TF900 company) made them for a short while until they finally went under.

I think the center of the coil has a weak response.

[Davor]

Sure, there is a null in a very middle, but surrounded by two highest peaks, one of which in counter-phase. Pinpointing in case of 4 quadrant rig is by finding a notch - you can't beat that.

[Polymer]

I'm back from my trip and did not get arrested at security for asking to take photos of x-ray of bigfoot.
I got some weird looks though and one employee appeared a bit stressed out by my request.

Anyway, I was not allowed to take a photo of the screen, but it was Ok to look at the monitor
until the next object passed through on the conveyor belt.

All I could definitely focus on in those short moments was the crossover at the centre of the coil.
The fine wires were very bundled and not as "spread out" or "loose" as in the x-ray pics from bklein.

I am not giving up on this and will take the bigfoot along on my next trip.
"If you don't succeed, try again"

Davor:
Yes indeed, the bigfoot coil has an extreme sharp dropoff in the middle when pinpointing. I find it fascinating.

I do not know what a 4-Quadrant rig is, but the xlt has an "absolute value" function which allows you to use
both halves of the bigfoot coil whilst pinpointing.

Thanks to all for your input so far!

[bklein]

I just got a Whites Classic SL cheap off Ebay. It has some issues... it had a bad VCC trace off the battery contact that I fixed, then it beeps continuously but does go solid sound when a target is under the coil. At first I thought it was a bad coil as when I pressed on the surface it sounded constant. That must have been a shield-related thing. (took it apart and see no intermittent issue) Anyway, the Inside Metal Detectors book gives me enough info that I should be able to figure out what's going on. There are several mods for this Classic series. Is there a mod that makes the Bigfoot work better than default? Is a bigfoot for the XLT (or any coil) for the XLT compatible with the Classic SL?

[Polymer]

There are nice pictures of the inside of several Bigfoot coils on the bay. For example this one:
http://www.ebay.com/itm/BIGFOOT-SEAR...8AAOSwNRBZlHji


Looks like the guy bought up the estate of Jim Karbowski or heirs.

Note the machine on the right hand photo for nulling the coils and all those reams of notes, gulp, is there something interesting there?

http://www.ebay.com/itm/BIGFOOT-SEAR...kAAOSwcmhZlHbE

Does anyone here live near Corvallis, OR ... perhaps you may find it interesting to get in touch with the guy.

The asking price for de coils, overblown for my taste ...

I´m in Europe, so a bit far for me to travel for now.

[kt315]

interesting... saved... thank you. i have to buy those paper folders at the right side LOL)))

[Polymer]

interesting... saved... thank you. i have to buy those paper folders at the right side LOL)))

You're welcome kt315. I'm happy to help the "Keeper of holy scripts" as I see you - Storing & organizing all those schematics & pictures ... wow!

Did you have a look at all the bigfoots and magnum offers from this guy on the bay? There are different pictures.

I did make a composite picture of one bigfoot with the magnifying function on the bay to get better resolution.
I don´t know if putting it here is a copyright problem, but I can PM it to you if you like.

Ha, the notes are up for sale now & includes all the email correspondence for reverse engineering - perhaps with whites/other entities at the time.

Here is the link in case it tickles your interest, yes you can buy, buy, buy:

http://www.ebay.com/itm/372054409056...=true#shpCntId

[Polymer]

Here some new pictures on the bay with the insides of Bigfoot coils.

https://www.ebay.com/itm/391926720369?ul_noapp=true

https://www.ebay.com/itm/372136558918?ul_noapp=true

https://www.ebay.com/itm/391926707656?ul_noapp=true

[bklein]

There is a thread on another forum where they give a bigfoot coil diagram (Russian?) with windings and configuration.
They give numbers by the coils of .35 and .22 but I don't understand what they are. Not AWG so what are they?
BTW, Bill Lahr really knows these coils. I had him repair mine for my XLT (had a bad capacitor and solder joint, causing falsing and poor ID). Now works great.

[Carl-NC]

They give numbers by the coils of .35 and .22 but I don't understand what they are. Not AWG so what are they?

mm
0.35mm = 27awg
0.22mm = 31awg

[kt315]

we here in EU and Russia too in metric system. so GB is gone on metric too but i do not remember when.
inch system is something crazy for me, 2,54cm is 1 inch. if i see 1/8' or 3/4 i bore in a stupor.

[BenGadget]

So....

I know this is an old thread, but I would love to make a BigFoot for my Dad to use in his MXT Pro.

I have 3D printers, and I am pretty good at designing in Fustion 360. Has anyone come up with a solution yet?