QTC Flashlights - Any problems in real world use?

Noob here. Stumbled across QTC lights such as the ones by Peak and Kuku and I'm wondering if anyone here has had first hand experience on the reliability of such things.

Mainly looking for the cons for QTC tech such as if the material wears out quickly/gets sticky/breaks down/etc. And would like to know if people prefer the infinite variable UI (just the concept) or would rather just prefer distinct modes (McGizmos piston drive) for a twisty/momentary switch combo. I'm thinking about maybe making custom lights in the future.

I don't like qtc lights. I haven't tried many of them but that's just my preference. Sometimes after i turn my light off and walk away, a few minutes later it will be back on, very very dim, but back on none the less. I have to remove the head when not in use so i can be sure it won't come back on. Also it only works really well when it's cold. Meaning if i pick it up off the shelf and turn it on slowly it ramps up nicely. But after it's been on for a minutes or so, it loses it's precision. No matter how slowly i tighten the head it seems to go from barely lit to high or max almost instantly.

I think the pros for QTC is that it is in a sense more reliable since it isnt mechanical and if it does "fail" the light will still work as a high only . Seems like there are many instances of mulitmode mini twisty lights having electronic failures over time.

Its also fun to play with and technically the output is infintely variable if you have the patience.

Cons are as mentioned above and also that if you dont do what Peak did and just throw a piece unprotected in your light it will wear out pretty quickly since it is delicate when exposed to twisting/grinding pressure like you get in twisty lights. Peak made a nice pill that protects the QTC in their lights and prolongs its usefull life

QTC material is spongy and doesn't expand back as fast as you untwist the light therefore you twist it till it's 'just' off and a few seconds later it's expanded to fill that gap thereby turning it on again albeit very dimly. The solution is simple. If you twist it half a turn to turn on, you should twist it half a turn to turn it off. Then you'll be past its maximum expansion and it won't come on again.
This is also the reason why it's more adjustable from a 'cold start'. Adjusting it from an already compressed state doesn't allow time for the materials natural expansion speed.

I think it's gimmicky. It jumps output when it wants to, same thing when it wants to ramp. It works fine for the first few days, then you get a hidden bonus strobe feature included in your light. Woohoo!

Some great comments on here. Looks like QTC isn't quite up to quality standards yet. I definitely won't be looking into building custom lights with this tech yet.

Ideally it would be a great material for flashlights, but it still has quite a ways to go.

QTC is ready for primetime
Battery-crusher technology is not the best way to use it methinks

QTC ramps up it's electron flow in an exponential fashion
the problem is, battery-crusher tech is linear

need some type of alternate method to squeeze the pill
maybe a watchmaker could design a rotational switch/mechanical gear system that will fit in the
light and squeeze a pill with ultimate precision, and unload it when done...
would cost far more than a driver though

would be an engineering marvel if a prototype was made

and I know there have been crazier things done with lights
---
or, ultra-uber never-before seen, fine thread pitch. twice as fine as Ti-Killer threads

I haven't gotten a hold of any of this material yet, but I'm thinking that a large ring of the material, sandwiched inside of a thin brass top and bottom ring would work better than a 'pill'. It would sit at the rim of the battery/light engine junction. By having a large area of QTC material to be compressed, there should be less compression required, more resistance to compression and so a little more tactile feedback, as well as more durability due to the pressure and current being spread across more material. -and the brass or whatever chosen metal top and bottom should take up most of the wear and tear, especially if these surfaces and the flashlight body surfaces were lapped to a nice polish to minimize friction.

I wouldn't build and sell product with it in for all the reasons noted above. However, I have it in a couple of applications, and absolutely love it. First is the Lummi Wee on my keychain. I can't say how convenient it is to have low through high. The other is as a control for a ~700 lumen headlight. Also very useful, but on the bad side, it adds weight and doesn't go to full power. Find it (with my username) on mtbr dot com forums. You might have to register to see pictures.

borrower said:

I wouldn't build and sell product with it in for all the reasons noted above. However, I have it in a couple of applications, and absolutely love it. First is the Lummi Wee on my keychain. I can't say how convenient it is to have low through high. The other is as a control for a ~700 lumen headlight. Also very useful, but on the bad side, it adds weight and doesn't go to full power. Find it (with my username) on mtbr dot com forums. You might have to register to see pictures.

Click to expand...

did this to my Wee too. had to thin-slice the QTC in half to make it fit reasonably

and to make sure the Wee is OFF, instead if simply unscrewing, I press the two halves together
(which brightens the light since the tiny gap between threads is enough to activate the QTC)
and unscrew until the light is off. then let go, and this ensures the QTC will not be compressed and bleed the batt.

but man it is nice to have a variable Wee

The QTC technology was made for variable-pressure touchscreens. I think the ideal interface would be as follows:

A microcontroller watches current flow through a QTC switch. An Analog to Digital converter turns current (from no touch to hard press) into a number that is used for exponential light output selection. This seems like a wonderful addition to click-to-pick multimode lights. ie, click = mode change, click+hold = infinite variable select.

Or it turns on as bright as you squeeze it. Harder press, brighter setting. All possible, right?

I'm tellin ya...

someone needs to carve a thin tube inside the barrel walls somehow
make it plastic, non-conductive
one end is a contact
inside is a pill, or even crumbled QTC inside this tiny 'cylinder'
the other end is a conductive piston head driven by a small gear
or threaded thingy

you dial up the pressure on the QTC. QTC cannot crumble and become
ineffective because it is inside this chamber. if it crumbles so what ? it is contained.
when the light is off the pressure is unloaded 100%.

it would take some time to engineer this but completely doable

battery crush QTC tech is just not the way to use QTC

127.0.0.1 said:

I'm tellin ya...

someone needs to carve a thin tube inside the barrel walls somehow
make it plastic, non-conductive
one end is a contact
inside is a pill, or even crumbled QTC inside this tiny 'cylinder'
the other end is a conductive piston head driven by a small gear
or threaded thingy

you dial up the pressure on the QTC. QTC cannot crumble and become
ineffective because it is inside this chamber. if it crumbles so what ? it is contained.
when the light is off the pressure is unloaded 100%.

it would take some time to engineer this but completely doable

battery crush QTC tech is just not the way to use QTC

Click to expand...

127, this post of yours has caused me to go from lurker to my first post. I've built a prototype that works similar to what you've described. It works great in this way, however it did take a bit of time and effort to get it working right. And now I am working on ironing out the kinks. I am planning to post the build on here in it's finished state.

Anyway, your insight inspired me to post Glad to meet you.