Electronics > Projects, Designs, and Technical Stuff
"No-crimp" connector idea
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tooki:

--- Quote from: ElectronicSupersonic on September 16, 2019, 05:49:02 am ---
--- Quote from: Gyro on September 15, 2019, 09:12:16 am ---Maybe I'm just not getting it, but I don't understand what stops individual strands from squeezing out into the open side of the 'omega' when compressed?  That would spoil the 'perfect fit'. Wire diameters will be subtly different between types too.
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Most multi-stranded wires are twisted, thus form sort of single core (especially when twisted some more, at least what's what I do before applying solder to the wire ends). Anyway in IDC connectors (say AVX Series 9176 http://datasheets.avx.com/StandardIDC_00-9176.pdf ) the slot for wire strands is open from one side (top) and strands going loose through that opening doesn't seem to be an issue. More other since the opening is omega shaped, the open part of it is somewhat narrower, thus to a degree should prevent strands from squeezing out. Another feature that could be done to enhance retention is an waist-like indentation perpendicular to the axis of a wire made in the middle of the contact "barrel".

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No, only the plastic housing is wider. The contact blades remain parallel.

I don't think you really understand the forces at work, namely, that you need REALLY significant forces on a wire to make a reliable connector without solder, which is why crimping is hard to do without the right tool. A proper crimp creates a cold weld; it's not just wires casually hanging out with the contact. That you are even thinking about strands "squeezing out" indicates that you don't understand how wire attachment works. If the wire is loose enough for strands to be able to work loose, then you are orders of magnitude away from the grip forces needed for a reliable connection.



--- Quote from: ElectronicSupersonic on September 16, 2019, 06:32:42 pm ---
--- Quote from: Simon on September 16, 2019, 09:01:33 am ---But this is still all relying on moderate friction?

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To a degree. It's more "the bite" that would provide retention in this instance.
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Yyyeah, no.



--- Quote from: ElectronicSupersonic on September 16, 2019, 06:32:42 pm ---
--- Quote from: ebastler on September 16, 2019, 10:33:04 am ---But then, why do you need the narrower opening of the Omega shape? If that is needed to stop the wire from slipping out of the eyelet, then you are obviously not holding it tight enough for good contact. So omit the narrow opening, and shape your contact as an steep "groove" with two parallel side walls. That will also accommodate stranded wire bundles of slightly varying thickness, which will fill the groove to varying height, while always being squeezed tightly in the lateral direction.
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The "bottle neck" is there for several reasons. One is to assist assembly — while inserting the conductor in to the contact, it spreads the thing apart (slightly) thus guiding it through.
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Huh? How does narrowing it "guide" anything? That makes no sense. There's a reason why the openings to so many things are funnel-shaped.


--- Quote from: ElectronicSupersonic on September 16, 2019, 06:32:42 pm ---Another function would be to affix it in the housing with dedicated protrusions. Plus it can serve as a spring to provide more pressure (provided the right shape of the contact and the housing).
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The force of a bit of springy metal is simply not enough to hold tightly.


--- Quote from: ElectronicSupersonic on September 16, 2019, 06:32:42 pm ---
--- Quote from: ebastler on September 16, 2019, 10:33:04 am ---Oh, now you have reinvented the IDC contact geometry.  ;)

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To an extent. IDC (as I understand it) solves two issues at once 1) No need to stripe the wire — thus no special tools required 2) No crimping needed (just a press-fit action) — thus again no special tools required. In IDC it's accomplished via blade like geometry that both cuts through the insulation and "bites in" in to the core.
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While IDC tooling is simple, it still needs special tools to do reliably. That's why there are IDC crimpers and presses for typical IDC ribbon connectors, and punchdown tools for the punchdown terminals which are omnipresent in telecom, which are also IDC just under a different name.


--- Quote from: ElectronicSupersonic on September 16, 2019, 06:32:42 pm ---With the contacts in question only the second one is true since a wire does need to be striped. Plus there is a larger area that comes in contact with the core (albeit a secondary contact).

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Except it's probably not as large a contact area as you think. With the insignificant pressures involved, there will be substantial air gaps (meaning not only air in there, but also formation of oxides over time). A proper crimp connection has a much larger contact area, since it squeezes out the air and actually cold welds the metals together!


Also, think about this: while the mating surfaces of connector contacts have continued to evolve continuously since, well, forever, the kinds of wire attachment to connector contacts have barely changed at all: we still use soldered, screw terminal, crimped, or IDC, for the most part. The fundamental geometry of each type of wire attachment side haven't changed much, either. (Nor do they vary much in principle between manufacturers, other than minor size changes to force you to buy expensive proprietary tooling.) So why haven't they changed? Could it be because we fairly quickly figured out what does and doesn't work?

I don't want to squash your enthusiasm, but this omega idea just doesn't make any sense to me. On the one hand, it's trying to solve a nonexistent problem. And on the other hand, the design seems to almost deliberately avoid firm pressure on the wire, insofar as it actually widens exactly where the wire needs to be squeezed the hardest. Again, I think there's some kind of fundamental misunderstanding about what the forces are that you need to design for.
ElectronicSupersonic:

--- Quote from: tooki on September 17, 2019, 08:38:29 pm ---...I don't want to squash your enthusiasm, but this omega idea just doesn't make any sense to me. On the one hand, it's trying to solve a nonexistent problem. And on the other hand, the design seems to almost deliberately avoid firm pressure on the wire, insofar as it actually widens exactly where the wire needs to be squeezed the hardest. Again, I think there's some kind of fundamental misunderstanding about what the forces are that you need to design for.

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It's quite possible that this design idea is a complete and utter BS since I'm not an engineer (I have a degree in design — not engineering). My intention was merely to share the idea. Whatever comes out of it (if anything) is OK with me.  :)
ebastler:

--- Quote from: ElectronicSupersonic on September 18, 2019, 03:26:51 am ---Whatever comes out of it (if anything) is OK with me.  :)

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I'm afraid that would be the wire, coming out of the contact clamp.  ;)
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