Mine did that one night as well, where it would turn off or blink twice from slight bumps to the tail. I thought to myself “gee, when I first got this light I was amazed at how unaffected it was to bumps.” The solution is to just tighten the tailcap more.
OMG!
Have the hardware designers learned nothing ? It is not as if they haven’t been told, repeatedly, by me, and Flashy Mike. And the fix is so easy.
This really is inexcusable.
I could rant on, but they just don’t listen. They just regurgitate the same old sad designs, no innovation, no progress.
I despair.
So I just hit the very tightened tailcap of my light and the problem is still there. 
Maybe Fireflies should be notified about how to fix it.
I don’t think they consider it a problem. In fact most flashlights do this. Part of the reason the ROT66 does this is it because it doesn’t have springs on both ends of the battery carrier. A longer battery, like a protected cell, will put more tension on the springs and make it less likely to be bumped and lose contact.
As far as modding the driver by adding a capacitor you would need to speak to Lexel about that.
Wasn’t that in reference to the xpl-hi being crushed? That has now been sorted.
I don't know, was it?
Well, Vinh has put this quote on his advertisement for his modified ROT66 on his website.
https://skylumen.com/collections/v54-lights/products/fireflies-r0t66vn
He also sells the ROT66 with Samsung LH351D.
I‘m quite surprised that Vinh has the guts to put such a statement on his advertisement for his modified ROT66vn. If I was Jacky from Fireflies I would not be amused at all to read “Poorly assembled from factory (Email 4 info)“ publicly, especially if there’s an official/unofficial business relationship between Vinh and Fireflies. For what it’s worth, there‘s nothing worse one could do to harm the reputation.
I ordered the SST20 6500K / 4000K with AUX Lantern, which is expected to arrive before next Wednesday. 
Vinh was the first one to report the problems with the xpl hi version onA CPF. Thats what he meant in the description
I have had my ROT-66 for about a week and have been testing it in the growing dark hours here in Alaska where I live. Here are my thoughts about this light:
Unboxing: A nice gift-worthy box with a magnetic close.
Size and weight: Compact: ¾ scale soda can format. About half the weight of my BLF Q8
Aesthetics: Champagne color. It is elegant. It looks like jewelry. A welcome alternative to basic black.
Emitter/Color: Mine has 9 XPL HI V3 3A. Natural White: I like it. Excellent color rendition. It’s like the noon sun is out.
Brightness: This is a ridiculously bright floodlight. It is the brightest light in my collection that includes Emisar D1, D1S and D4 lights as well as the BLF Q8. How many lumens on Turbo? I don’t know. But it is considerably brighter than my BLF Q8. (Both are powered by new button top Orbtronic ORB-3120 batteries – rewrapped Sony VCT6 - which each kick out 30+ amps for a few minutes.)
Throw distance? Definitely not a throw light. Yet with this much brightness, useable light reaches out a couple hundred yards – only slightly less distance than the Q8.
User Interface: I only use ramping or two-click Turbo. It is intuitive. When ramping up there is a quick blink when it reaches maximum brightness.
Carrying ease: If I am wearing baggy jeans or an overcoat, it is pocketable where the Q8 is not. It also comes with a substantial lanyard which screws into a tripod hole. The lanyard color is also champagne.
Heat management: It gets hot quickly on Turbo. Any longer than 60 seconds requires gloves. During winter in Alaska this heat can be useful. At lower brightness, heat is not an issue.
Fun feature: A glow-in-the dark ring surrounding the LEDs is activated by the brightness of the light. It glows a very attractive blue.
Summary: This is an elegant, small soda can light. This is a ridiculously bright floodlight. This is a useful and well-built light. It will live in my Bentley’s glove box.
Did anybody notice that batt+ goes to the bottom of the battery carrier through one of the three rods? Its the one whose screw is sealed on the top (edit: probably just a rubber plug without screw). So we might get USB charging with an extra tailcap one day.
Or I build a light like my Q8 Janus with less effort …
I suspect there is a major flaw in the battery carrier.
Did some measurements and this are the results:
67 mm is the space between positive cell contact and fully compressed spring at the negative end.
63.7 to 64.7 mm is what I measured with uncompressed springs.
I used this light for about one day mostly with only 1 cell (30Q with flat top), I guess this cell sat where I measured 64.7 mm which means this spring is already worn out a bit (after one day of usage).
According to datasheet a Samsung 30Q may be as short as 64.7 mm. My button top 30Q has 67 mm length, so I can’t use either of them reliably.
With this findings I even doubt a buffer cap alone will help in the long term against power loss on bumps, this light needs better springs (if my light isn’t just an isolated case).
Would anybody measure the named dimensions as well and post his results?
I measure 63.1 to 64.1 mm with uncompressed springs.
The batteries I’m using are 65.2 mm long.
I can’t get mine to interrupt power by bumping the tail of the light.
I intend to try the buffer cap mod but I can’t open the driver retaining ring. My Camera Lens Opening Tool doesn’t grip in the strange conical holes. Is the retaining ring glued? I thought only the driver itself has glue. Are this lefthand threads?
Any help appreciated!
Yes Vinh was referring to the crushed emitters and/or misaligned emitters he got when talking about poorly assembled. He loves the design and quality of components on the light otherwise.
The driver retaining ring is threaded normally, not reverse. However, it is a bit stiff. I don’t know if it’s normally glued, but I asked specifically for a light with no glue anywhere, because the whole point of me having one was to open it up for development purposes. Glue would defeat the point.
Thanks!
I’m not sure if I should heat the head with heat gun. There is plastic inside. Don’t want to destroy anything. Since I’m not in a hurry I might wait for someone else taking the risk 
.
But I might drill two smaller, not conical holes into the retaining ring for more grip with my tool.
Btw., there have been some strange inconsistencies in lumen measurements done by members. Might these have happened due to poor battery contact?
i just saw the movie (again), 30 days of night…makes me want to visit. with a months worth of batteries, of course
SST20 95 cri version ordered. Will have to have a nice little bout between the Nichia SW45k R9080 version, Samsung LH351D+804 filter from Vinh, and this SST-20 version.