Chance PI coil...

[baum7154]

NEW TEST RESULTS FOR 3DSS RACETRACK COIL ON MODIFIED CHANCE PI

This is a partial repost of the 3DSS RACETRACK COIL test results on simulated ground from the 'Chance PI Build' thread in the TECH FORUM.

I decided to run some target sample tests as a comparison point to previous tests for First Detection & Detector Tone Lockup with the standard being three consecutive passes to validate the distance. The problem is air tests are inaccurate for determining true depth in soil. The second problem is that everything here is covered in a foot of snow. Forum member ANDY (6666) suggested another test method a while ago placing the coil on the ground and passing the standard targets over the coil. This has the effect of reducing the detection distances of air tests and is more realistic in its results I believe. Since doing the tests outdoors in this season is not possible I found a quiet spot in the concrete floor of my basement where fortunately no steel re-bar has been placed and set up the detector with the 3DSS coil resting flat on the carpet and began passing the targets over the coil with a plastic ruler vertical in the coil, for distance measurement. I took the extra step of placing two packets of black sand 2" over the search coil, equivalent to about 2 teaspoons spread over 5 square inches. The following are the test results:

TARGET-----------------------1st DETECTION-------------------------------TONE LOCKUP

ALUMINUM SODA CAN---------20"--------------------------------------------15"

STEEL BOTTLE CAP-------------14"--------------------------------------------9"

US NICKLE----------------------10"--------------------------------------------8"

US SOLID COPPER PENNY------7"---------------------------------------------5.5"

US SILVER DIME----------------7.75"------------------------------------------5"

8.5 grain DENTAL GOLD--------3.75"------------------------------------------3"

4.5 grain 14kt GOLD HEAD-----3.0"-------------------------------------------2"

1/4" X 1/4" SODA CAN WALL---2.75"-----------------------------------------2.25"----Note: Solid tone detection distance has improved 1.5" from similar over soil test of last summer.


I believe these modifications have improved the performance of the CHANCE PI and enable the 8" 'blade' search field of the 3DSS Racetrack coil to better detect small gold even though it is only 4" wide.

Regards,
Dan

[Darin]

Thanks for the info Dan, that gives me something to compare my coil to.
Was going to try the damping tool tonight and see if I could get better depth with mine but seems like my threashold pot is not working. I checked it with my meter and its intermittent and the audio is just a high pitch tone. Have to get another 220 pot and see if that's what it is.

[EasyX]

Hi, i am thinking about making 1 or 2 coils like described here.

What i am confused about are the total coil sizes. Somewhere i read about 4" x 12.5" But which size? Inner? Outer? or Middle? What is the commen sense to use, if not mentioned?

And another question, would it make sense to make a big (~11") coil with this 3DSS pattern? Or would a simplier design fit for that purpose?

And a third question, would i need to make any change on my MiniPulse Plus (Rev D)? Because somewhere i read something about making an adjustment for using fast and/or slow coils. (actually i dont even now what defines fast an slow coils)

Greetings

Isaak

[baum7154]

Hi, i am thinking about making 1 or 2 coils like described here.

What i am confused about are the total coil sizes. Somewhere i read about 4" x 12.5" But which size? Inner? Outer? or Middle? What is the commen sense to use, if not mentioned?

And another question, would it make sense to make a big (~11") coil with this 3DSS pattern? Or would a simplier design fit for that purpose?

And a third question, would i need to make any change on my MiniPulse Plus (Rev D)? Because somewhere i read something about making an adjustment for using fast and/or slow coils. (actually i dont even now what defines fast an slow coils)

Greetings

Isaak

------------------------------------
Hello Isaak,

The size of the Racetrack 3DSS coil is 4" X 12.5" measured to the center of the coil bundle. This made the most sense to me since the coils tend to spread out and it seemed that these dimensions most closely represented the point of greatest coil density.

The 11" coil make sense for general detecting for coins but it should be 8" or smaller for smaller gold

You will always need to set critical damping for any coil change to get best performance.

Hope this helps,


Dan

[EasyX]

Thanks for your answers!
Just build a 11" coil today, probably going to build a smaller one soon. How does the 4*12.5 behave compared to a 8"? Is it nearly the same depth in general, but has th he advantage of a blade shaped magnetic field?

[baum7154]

PERFORMANCE OF 3DSS RACETRACK COIL VS 3DSS 8" ROUND COIL

Thanks for your answers!
Just build a 11" coil today, probably going to build a smaller one soon. How does the 4*12.5 behave compared to a 8"? Is it nearly the same depth in general, but has th he advantage of a blade shaped magnetic field? [ATTACH]36002[/ATTACH]

--------------------------
Hi Isaak,

You have built a beautiful coil!
As my test results posted in this thread indicate (post #179 & most recently #271), the Racetrack does give up a small bit of depth (about 1" on the small gold target I seek.) owing to its 4" coil width. That is offset to some degree in having a fairly constant sensitivity about 8" long, down the coil center, allowing the coil to cover ground much more quickly. Also this coil fits into tighter spaces. The detection blade field of the Racetrack coil is quite 'sharp' so a rapid search sweep speed is not desirable when using it.

Round coils have greatest depth and sensitivity at a pinpoint about 1 radius out from the coil center. On an 8" coil that pinpoint would be at about 4" out. By the way, in my tests I use the standard of three consecutive detected passes for the 'first detection' and the 'tone lockup tests' on my modified Chance PI. My detector/coil does see targets at greater distances but it can be inconsistent so I don't use those test results . However when in the field if I get sporadic 'hits' over the same spot 5 out of 12 passes I'd probably dig the target up.

Regards,

Dan

[EasyX]

Thanks for the explanation Dan!

Just build a 4"*12.5" coil. I used a little different wiring technique, just 2 instead of 3 steps forward each time. This results in making the extra single step forward every 3 instead of 5 turns. I didn't consider that I need much longer cuts, so I had to stabilize everything with some tape. At the end I made 30 turns. Optical it looks good, nearly all crossings are rectangular, but I will see if it's good in real.

[baum7154]

Hi Issak,

Have you tested your coil yet? It will be interesting to see how it performs compared to the original pattern especially on a 1/4" square piece of a soda can cut from the middle of the side wall.

I look forward to your test results.

Dan

[Matt_Rowe]

Basic same design as the bigfoot coil by Jimmy Sierra.

[baum7154]

[QUOTE=baum7154;216971]Hi Issak,

Have you tested your coil yet? It will be interesting to see how it performs compared to the original pattern especially on a 1/4" square piece of a soda can cut from the middle of the side wall.

I look forward to your test results.
----------------------------------------------------------
Issak
Have you done any testing on your coil yet?

[Tauc]

I will probably be building a Mirage PI over the winter and this coil to go with it (or maybe i should build the chance PI? has anyone tested both and can recomend one?). The "original" Mirage search coil is rated 300uH so i want to match that when building this one but im not sure how to achieve that while not having an oscilloscope. how do i know what AWG the wire should have and how many turns to get 300uH (or at least close to it)? I plan to make the 8" "spider" coil.

[baum7154]

I have built and done modifications to the CHANCE PI for the past 4+ years and have spent about the same amount of time on the
3DSS coil detailed in this Chance PI COIL thread . Many test results for the CHANCE PI detector are detailed in the Chance PI Build thread and in this Chance PI Coil thread as well.

An 8" spider coil, a spiral coil, or a basket weave coil is not the same as a 3DSS coil because it does not self shield. I would use 24awg or 26 awg 600volt teflon insulated stranded wire with the feed line being a continuation of the coil wire but twisted at about 3 turns per inch. This twisting is easily accomplished by chucking the ends of the coil wires in a drill chuck and giving them a spin with gentle tension at each end of the wires. There are details for the number of turns on an 8" 3DSS coil in these threads.

I hope this helps.

Dan

[dantech]

.

[cabla33]

i have read the complete thread, butl i wonder how to calculate this coil?
do you simply use the coil-calculator for this? if so what about the inner and out diameter?
an example for calculation of 5''-circle-version would be nice.

[homefire]

I use the coil housing as a guide . Outer diameter is what will fit within the outside walls of the form. Inner the same. Pick your wire size and target uH and run it. Remember to leave room for Wrapping and Shielding.