M11 Coil Mod, Cut Out Struts, Light And Fast Underwater

[TTT2866]

11 minutes ago, Tony said:

Xrays of the coil. I can see the bits you were referring to on the right hand side of the coil.

Hard to know where the problem might be....others might spot something though.

I wonder why those two struts that were removed had epoxy ?

More likely you nicked an artery off to one side (probably the Rx side on the right), especially if the windings weren't central and were to one side a bit when potted.

 

That's a great image, I'll do a side-by-side tomorrow and see if I can find where it went wrong. Cheers!

[fishersari]

20 minutes ago, Tony said:

I wonder why those two struts that were removed had epoxy ?

I think the epoxy helped with the robustness/minimizing bump effect on the tx side or it needed stronger frame for tx since it has much more coil winding than rx .. i dont know.. lol

[PimentoUK]

A few observations from an electronics guy:

Re: X-rays: The chunky bundle of wire is the transmit coil, which connects directly to the screened cable integral to the coil cable, you can see the two solder-joints. The thin wire bundle is the receive coil, which connects with two wires to the small vertically-mounted PCB, but there will almost certainly be a shield wire wrapped around the RX coil in some way, that also goes to the PCB [based on how the Eqx is wired up ]

There shouldn't be any other wires anywhere else - the general idea is the wiring is kept very short, for techy reasons. The PCB is half-way down the coil length so that any electrical 'imbalances' are symmetrical. [ notice the Eqx has the PCB offset down one end in the fat spoke - I suspect ML decided this wasn't good enough for the Manti ]

It could simply be a mechanical problem that's caused the coil to no longer function. Removing the ribs allows the coil to change shape, there will be stresses inherent in the structure, the coil is assembled and fine-tuned with those stresses. Subsequent modifications can then ruin this fine-tuning.

Example: Take a flat piece of sheet steel 1.6mm ( 1/16" ) thick, put it on a surface grinder and machine off 0.3mm from  one face. Remove it from the grinder, and you will find its quite significantly curled up, not at all flat. This is because the rolling process stresses both outer skins of the steel. Both are the same, so the steel is flat. Remove one skin, it's all out of balance, one skin is 'tight', the middle section is 'neutral', the bend is the resultant.

Unfortunately, trying to 're-fit' the ribs adequately would be a heck of a job, you would need to observe the coil output signal ( eg. on an oscilloscope ), and see what insertion/removal changes do anything worthwhile.

 

[Caliche]

Are the spokes with light grey interior simply filled with epoxy, or are there also strips of sheet metal in there?  I'm no expert at reading X-rays.

[Johnnysalami1957]

Minelab took the ribbing idea from another product because it implies "pleasure" to some users.

[Tony]

9 hours ago, PimentoUK said:

The chunky bundle of wire is the transmit coil,

Good to know.....for some reason I thought the Rx was on the right. Must have been one of those generic pictures showing Tx / Rx

[Tony]

11 hours ago, TTT2866 said:

That's a great image, I'll do a side-by-side tomorrow and see if I can find where it went wrong. Cheers!

.......we all love a good autopsy 😑

[TTT2866]

On 12/5/2024 at 9:39 PM, fishersari said:

Would love to see your custom made skidplate

 

23 hours ago, fishersari said:

Oh no.. is it possible for you to attach pictures of the coil? would love to find out the source of the problem.. maybe the epoxy has micro crack due to vibrations while sawing the ribs and exposed the coil inside.. do you submerge the coil at the beach?

There was a thread by @strick regarding coil xray.. if I remember correctly there was nothing such as coil wire or antenna near the ribs or inside the ribs

Edit : found it 

https://www.detectorprospector.com/topic/10222-whats-in-your-coil/page/7/#findComment-222123

Here's a photo of the custom skidplate plus the cut-off pieces. I made the skidplate using a wooden mold/copy of the coil and a heat gun.  I had a pretty close look and couldn't see any copper pieces sticking out of any cuts. 

 

Thankfully my old colleagues are hooking me up with a discounted replacement coil at a pretty good price. 😄 

[fishersari]

Welp I'm bowing out from coil mods too.. its seems to me there are nothing wrong from your mods from my naked eyes except maybe the the epoxy cant withstand the vibrations/pressure from the rib cut, maybe in between the exposed epoxy from the cuts and the coil casing itself has micro air gap and let water sip in as you said the coil has no issue on your testbed.. problems occurred at the beach.. 

Did you use hot gun for the skid plate on the coil itself? If yes I wonder how high was the temperature needed to bent the skid plate