Author Topic: Idea for a switch  (Read 472 times)

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Offline Kevadu

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Idea for a switch
« on: Tue, 06 February 2018, 21:56:04 »
As the title implies this is really no more than an idea right now.  But it's something I've been thinking about and I thought I would share.

Here's a crappy diagram of what I have in mind:


The actuation method is about the simplest, dumbest thing imaginable.  There are two contacts near the bottom of the housing and a plate near the bottom of the slider that's either made out of or coated with something conductive, so when it hits the contacts it completes the circuit.  Now ordinarily this would be a dumb way to do things because then you're actuating when you bottom out, but bear with me for a minute.

What I have in mind is that the bottom plate is not fixed.  Instead it can move independently from the rest of the slider.  There is a second outer spring that normally keeps it pressed down (that is supposed to be one spring that wraps around the slider, think of the diagram as like a cross-section) and a small lip on the bottom part of the slider to keep it in place.

I hope you can see from this how since the bottom plate can move you're not actually actuating on bottom out anymore, as you can continue to push the slider forward.  But make this transition from pressing on one spring to two springs, which will produce a kinked force curve like:

Where the kink happens exactly at actuation, since before that you're only pushing on one spring.

This funny-looking force curve was actually my true objective in this design.  I'm looking for a tactile switch where the force actually increases at/post actuation.  In most approaches to tactile or clicky switches there is a bump in the force curve prior to actuation and then a sudden drop around actuation.  This makes it easy to overshoot the actuation point and bottom out.  Indeed there are a lot of switches where the peak of the tactile bump is close to bottom-out force.

I want some tactility so you know by feel where the actuation point is, but I want to strongly discourage bottoming out at all.  My experience with Halo True switches has convinced me that this is a good idea.  Indeed they're very close to what I'm looking for.  But I still wish they had sharper tactility, so the actuation point was instantly recognizable.

Which can be achieved here by preloading the outer spring.  See in the above force curve I assumed that the outer spring's rest position is naturally the distance between the two plates.  The result is fairly subtle, a change in the slope of the force curve but no distinct bump.  But what if the outer spring was already partially compressed?  So there's already a force on it but it's held in place by the lip on the slider.  Well once it hits the contacts you have to first exceed that existing force before you can move it any further, leading to a clear bump in the force curve:


That's just the general idea.  The exact shape of the force curve can be altered significantly by adjusting the weight of the two springs and the amount of preload.  A very light outer spring with no preload would feel almost linear, with just a subtle change in slope at actuation.  A heavy outer spring would produce really heavy bottom out forces without necessarily requiring any more force for actuation.  And of course the amount of preload would affect the size of the jump in the force curve at actuation, though I suspect this wouldn't need to be large at all to be noticeable.

But this is all academic at this point because I'm no switch manufacturer.  I do wonder how difficult it would be to build a switch like this.  Of course the whole dual spring and slider on top of slider thing sounds like it would significantly complicate things, but on the other hand you do with a fair bit by having such a dead simple actuation mechanism.  And while the design is quite different I don't see any fundamental reason you couldn't fit this inside a MX housing for compatibility.

Thoughts?

Online suicidal_orange

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Re: Idea for a switch
« Reply #1 on: Wed, 07 February 2018, 03:08:39 »
I like the look of those force graphs and love the story like description of how it works but am struggling to think through how this is put together.  I guess you take the green bit, add the sliding plate, put two outer springs on the red spikes in the inverted switch lid (which has the fixed plate as part of it) then insert the green bit?  This would mean you have to hold the stem poking through the lid to put it on once the switch is installed in a board, which is tricky.

Or maybe you were thinking one big outer spring around the green bit?  That would be easier to fit (could balance it on the inner spring as with Cherry switches) but it would put constant pressure on the middle of the moving plate meaning it would need to be thicker so it doesn't deform.

I also worry about the mechanics of repeatedly bashing a conductive strip onto two conductive spikes - assuming they're metal won't that be noisy?  Will the contacts wear away?

Interesting idea, thanks for sharing :thumb:
                               
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Offline sinusoid

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  • fd > ESC
Re: Idea for a switch
« Reply #2 on: Wed, 14 February 2018, 13:07:48 »
If you swapped the contacts for springs, perhaps on a leading rod, you could achieve the same result without added complexity of the suspended contact plate.

I like this, it looks like a non-membrane tactile variant of Cherry MY.

Online BlindAssassin111

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Re: Idea for a switch
« Reply #3 on: Wed, 14 February 2018, 13:43:03 »
It is similar in concept to a switch design I have seen somewhere before, but I can't remember what it was sadly... And it isn't a bad thing that it is similar.

Only input I have is that your force curve would not have a "bump" feel when using it, it would just suddenly feel heavier. A bump for tactility requires a drop in force after to be something you can feel as such. So you would have a progressive switch, not linear which increase force linearly, so it would just be a different "linear" switch type feel.

Offline E TwentyNine

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Re: Idea for a switch
« Reply #4 on: Wed, 14 February 2018, 13:52:36 »
I think you might be able to accomplish the force curve you want simply with a progressive spring.

Softer part compresses first, tighter wound part compresses later.
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Online Kavik

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Re: Idea for a switch
« Reply #5 on: Thu, 15 February 2018, 10:16:24 »
If you swapped the contacts for springs, perhaps on a leading rod, you could achieve the same result without added complexity of the suspended contact plate.

I like this, it looks like a non-membrane tactile variant of Cherry MY.

I've thought of something like that which uses four guide rods on the corners to reduce wobble. I'd be concerned about increased friction and fragility though.

Offline sinusoid

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  • fd > ESC
Re: Idea for a switch
« Reply #6 on: Thu, 15 February 2018, 11:08:15 »
Whipped this up really quick for sh&ts & giggles
188943-0

.blend file here:
* GH_Kevadu_linear_sw.blend

@Kavik
- Cherry MY solves side wobble by having a square profiled teflon-ish stem.

@E TwentyNine
- this is a great idea, made me think of two co-centric springs of different diameters.

@BlindAssassin111
- yeah, I swear I've seen a mechanism like this somewhere before.

Offline ErgoMacros

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Re: Idea for a switch
« Reply #7 on: Thu, 15 February 2018, 11:14:06 »
Beautiful render.  :-)

So, activation happens when the bottom of the white piece shorts out the 2 side springs?
Might this (contact based upon springs) extend the "bounce" time for the contacts?
Today's quote: '...“but then the customer successfully broke that.”

Offline Leslieann

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Re: Idea for a switch
« Reply #8 on: Thu, 15 February 2018, 19:53:52 »
Start with Blues and do the o-ring mod but with the softest o-rings you can find (foam or sponge might be better).
Filco MJ2 L.E. w/Vortex case, hand milled case, custom feet, custom paint, Klaxxon key caps, lubed and o-ringed Jailhouse Blues made from vintage Cherry MX Blues, HID Liberator, stainless steel universal plate, 3d printed adapters, removable cord, sound dampened. Winkey blockoff plate | Magicforce 68 w/Outemu Blues |KBT Race S L.E. w/Ergo-Clears, custom WASD keyset | Das Pro w/browns (Costar model) | IBM Model M (x2)