This would be a great change.
The L8 uses a 1.5mm diameter spring because its current is as high as 25A.
The maximum current of the M3 M3-C is only 10A, so it is not necessary to use such a thick spring.
Not thinking about current, just about the past discussions in this thread about the spring being too weak in the M3 lights - they will turn off or cut out/blink when bumped softly. The 26650 and 26800 cells seem to be too heavy for the single tail spring but we thought a stiffer one would be a good solution (that or two springs in the light instead of the brass post on the driver). The spacer boards don’t fix that problem even with 2 or 3 of them (too much). So far the best solution has been to add an old P60 drop in spring (just sits on top of the retaining ring loosely, in addition to the stock spring…sort of works). One guy used a short piece of rubber hose as a cushion inside the stock spring. So I was hoping this new thicker spring might be the answer for the M3/M3C. 
This is because the battery tube in the middle of the flashlight is too long.
you can solder a spring on the spacer board
As long as strobe mode with mode memory is still possible, and it is a 10Hz strobe.
Sadly too many flashlights now have hidden, and alternating frequency strobes.
On these newer designs with only one side having a spring, the slightest shock load interrupts current flow. Traditional springs on both sides allowed cells to bounce back and forth without loss of contact. Traditional double ended springs also kept the positive side of the battery from hard impacts into the bottom of the circuit board. If that brass contact stud is denting batteries on impacts how far away is board damage. Granted newer boards have little space left of springs. These impact interruptions on current cause mode changes, or lights to go off. The more important the lights use the more critical an issue this becomes. When I did traffic control just waving some of the newer lights made them unusable from constant mode changing. A dropped light can be picked up, a dropped light that just turned itself off has to be found.
It’s very annoying. Was thinking of the FC40 1800K as a nightlight. But this is a no go for tail buttons flashlights. You turn it on, switch to the level you want and put it down. And it switches level! Have a M21B and S11 and both are not suitable for tailstanding because of this. The M21B is not too bad, but the S11 is unusable for this purpose. Which is a shame, because the thicker S11 makes it more stable. Don’t get me wrong, they are nice lights, just not for tailstanding. I’m putting my hopes on the upcoming side switch lights.
Thank you for posting that 1800-2000K measurement Simon. Looks good and I’m really looking forward to it. Also, the colour temperature in that measurement is my birth year. A must buy 
Yup, in a M21B. But it’ll take a while to arrive.
I think that would be excellent as well! If all the blinky modes including strobe could be enabled or disabled, you could remove several of the duplicate mode groups as well. I think that would be a significant improvement!
I’d look forward to a newer UI. Having a double click to max would be so much better – keeping a ceiling of 60% or so in the main sequence. As for the fixed frequency strobe, that 4th option would be best for some light painting (more so if it can be also memorized) and at the same time remove some of the redundant mode settings.
But I won’t get ahead of myself as there’ll be many cooks that will chime in. Simon did rightfully say “this may cause disputes”.
There are now only a handful of tailswitch 18650/21700 tube flashlights suitable for light painting (or at last creating light trails). So, if Simon can have a memorized 10Hz strobe, that would result in quite a few extra sales.
There are red osrams on stars in the convoy store at the moment:
https://www.aliexpress.com/item/4001334292126.html?spm=a2g0o.store_pc_groupList.8148356.2.54de24bfT0p4JK
These are Vf ~ 2.5V and I ~ 2.5A max LEDs.
Datasheet:
But the current convoy drivers seem to bottom out around 6A.
Is there any chance of convoy adapting some existing 12mode drivers to 2.5A drive?
So for me, the biggest missing UI feature is a way to configure the group you’re using to hit the LED’s sweet spot. When I swap the LED, chances are the sweet spot is not at 50% (groups 7,8 and 9) or 100% (all other groups).
For example, my L21B with 8A driver: swapping in an osram w2 or a 519A: I would either miss out on a lot of performance at 4A (groups 8 and 9 at 50% max) or I would overdrive it at 8A… I’d rather use around 6-7A.
—> How about a new config menu to just scale the current group to a % of max, say, by 5% increments (20 steps) (or maybe 10 steps between 50% and 100%… something like that):
- If I want 6A on group 6 (100, 20, 1) : scale to 75 of max = click 16 times (out of 20) in the config menu
- If I want 5A max on group 2 (.1 1 10 35 100): scale to ~60% of max = click 12 times
- If I want 5A on group 12 (100% only), scale to ~60% of max = click 12 times
This would allow to hit the sweet spot of any compatible LED without changing driver. Actually, I guess I’d have to buy new flashlights with this new driver…
The light this emitter produces looks fantastic!
Very much looking forward to purchasing a couple of M21F units that I will be running continuously as interior lighting off the USB charging cable, without batteries inside (no worries about the battery degrading/overheating when there is no battery inside to begin with).
Running only off the USB cable, at 2A over 5V means 10W power per M21F unit, ceiling bouncing a couple of units and any small room will have a super cozy quality of light (for night use) that is very hard to obtain, I have never seen a high CRI 2000K light bulb if one exists in the first place.
Sure, but it’s 17mm only, and the new red is on a 20mm star. To be fair, I have not searched very wide for non-sofirn red drivers yet.
Simon, I’ve noticed the exact same behaviour on my L6 GT-FC40. Same included Liitokala Lii-50A batteries, currently 3.8V. Unfortunately I don’t have any other 26650 cells lying around to try with.
I haven’t been able to always trigger it on command, but I did manage to film it. It took about 10 attempts before it finally showed up when filming. Start with 10% mode and then it blinks and goes to 1% mode (seems to memorize the changed mode). It seems to occur more when the flashlight was unused (so it’s room temperature).
Do you have access to youtube there? If you do, maybe this short clip helps identify the problem; https://youtu.be/NuawEqGuNgk
It is more likely that the battery voltage drops a lot under high current.
Figured as much, that’s why I didn’t report anything until I saw there are more people having the exact same issue. Maybe the Lii-50As are not the best choice to include in this specific setup. It’s always when the flashlight was just turned on, I’ve never seen it otherwise. If it does I’ll let you know.