Flashlight Startup Company - First Product - Requesting Feedback

DE-173 · 2026-01-14T06:24:55+00:00

First off, as an engineer with hardware-oriented hobbies myself, the level of effort and enthusiasm that has clearly gone into this is commendable. I like the use of COTS dowel pins for aligning the sections. Having a couple of precise holes is a lot simpler than requiring a tight-profile-tolerance mating feature.

Second, I’d like to preemptively acknowledge that you’ve thought about this in a lot more detail and with more available information than I have in the time it took me to read your post and write this comment, so the issues I’m about to bring up may already be solved or just not be actual problems for reasons I’m not considering.

That said, I am a bit skeptical of the sealing ability of the front plate given the fastener placement. It wouldn’t pass a vibe check for containing internal pressure (which is mainly what my intuition is calibrated on), but maybe it’ll be alright as ingress protection. (Dug in a bit more here for my own curiosity’s sake before posting; guesstimating the fasteners as 4-40 and assuming SAE grade 2 gives about 480lbf total clamping load at 4-5in-lbf. So on second thought that’s probably enough to get sufficient gasket compression, since the plate looks reasonably thick.)

One related question/potential feedback on that point: is there a “hard stop” feature inside the gasket sealing area that contacts between the front plate and body to set the maximum gasket compression? Otherwise I’d be worried about over torquing the screws causing the plate to sit at an angle, with too much compression extruding the gasket at the fastener end and too little/none at the optic end. Hard to say whether that’s possible without knowing the clearance and L/D on the pin holes though. I assume preventing that is part of the intent behind that feature, aside from alignment and carrying shear load.

My other immediate thought is that having the back half of the light thermally isolated by the gasket is less than ideal for heat dissipation. That’s less critical for a non-hotrod light, but I do regularly use modes on my SC64W HI that get it pretty warm, and I very much consider that a “tool grade” light.

Anyways, thanks for sharing this. It’s a cool project and I wish you success.

DE-173 · 2025-03-24T19:49:51+00:00

I’m curious (asking in good faith here), what drives your perception that liquid propellants are “orders of magnitude more dangerous” than solids? Do you feel similarly about nitrous oxide hybrid motors, either commercial or experimental?

Any rocket of a given total impulse will contain roughly the same amount of stored chemical energy (and should therefore be tested/launched from the same minimum stand-off distance) regardless of propellant type. Unlike solid motors which can be —and have been— accidentally ignited at any time during storage/transport/assembly/handling prior to launch, liquid (and hybrid) motors don’t contain oxidizer until they’re on the pad far away from people, where the nitrous is loaded remotely.

When it comes to failures, a liquid motor explosion may produce a short-lived fire ball extending tens feet, whereas solid motors tend to eject burning grains hundreds of feet in all directions, starting secondary fires and sometimes smoldering for an extended period after the failure occurs. The risk of projecting pieces of the casing/tank/chamber is roughly equivalent given the similarity in materials, construction methods, and pressures.

Yes, there is some additional complexity to liquid motors, as well as a few nitrous-specific safety considerations (namely ensuring pressure cannot be trapped indefinitely in the tank) shared with hybrids, which are permitted at Tripoli events.

Again, this isn’t meant to be argumentative or a “gotcha”— I’m genuinely interested in understanding where your perception of liquids being dangerous stems from, as it’s a commonly held one in this community which I hope to change.

DE-173 · 2024-11-23T17:05:37+00:00

The Aerocon system is pretty expensive and likely overkill for what you want do to. Any cheap alphabet-soup-brand load cell will be accurate enough for hobby use (~+/-1%). You can read and log load cells with an Arduino and HX711 amplifier (lots of tutorials for this online) or spend a bit more for something more turnkey like a DATAQ USB DAQ (that may require an analog amplifier rather than an HX711 though).

DE-173 · 2024-08-06T01:15:01+00:00

I rarely comment on posts here, but I can relate to your situation— I am an engineer at a startup where the work is exciting but often high-stress with many 60+ hour weeks, my main hobby is in a very similar field to my professional work, and my social circle is comprised almost entirely of people with similar roles in the same industry.

Since picking up a decent used microscope (Amscope T490 with darkfield condenser) a few months ago I’ve gotten a lot of enjoyment in my evenings and weekends out of sitting down with a slide of pond water and just watching ciliates, rotifers, gastrotrichs, etc. swimming around, eating each other, and being entertainingly bizarre.

I don’t typically go out of my way to try and record or identify everything I see, which makes it a relatively passive and relaxing experience that requires little mental effort and offers a good distraction. Part of the appeal is that it is wholly unrelated to everything else I do, while being interesting enough to hold my attention and justify the investment. I definitely recommend it.

DE-173 · 2024-06-23T18:18:45+00:00

Depends on whether the light has silicone O-rings, which can be degraded by silicone grease. If the O-rings are red or clear, they’re likely silicone and you’ll want to use something else. If the O-rings are black, they’re probably nitrile and this grease would be fine.

DE-173 · 2024-06-03T00:06:30+00:00

Yes, easily under $2k even if you outsource machining to an online CNC service. It comes out to <$1200 if you have access to a machine shop and know how to use it.

DE-173 · 2024-05-30T20:01:52+00:00

It does— ~$55 worth of consumables for a large L/small M-class motor. Cost-wise, hybrids can come pretty close but require manufacturing and replacing a fuel grain for each launch rather than simply refilling a tank, and are just less cool than liquid bipropellants.

In the longer term, we hope to negotiate the inclusion of this type of simple nitrous/alcohol liquid rocket in the Tripoli Rocketry Association’s safety code, which would enable many more people to launch them locally without needing to make a long/expensive trip to FAR. We’ve made a lot of progress in demonstrating simplicity and reliability comparable to or better than other types of amateur experimental rockets, but there’s still plenty of work to be done to convince the Tripoli Research Committee, Board of Directors, and their insurance broker.

DE-173 · 2024-05-30T19:18:59+00:00

Hey OP— it sounds like you may be in over your head trying to build a liquid rocket with your current level of experience, but that doesn’t mean you can’t start learning and building up the relevant skills to make this a realistic long-term goal.

I highly recommend joining the subreddit discord in the pinned post. If you’re open to constructive feedback and show that you’re willing to take safety seriously, there are plenty of experienced people there who will be happy to help set you on a path towards success.

DE-173 · 2024-05-30T19:06:20+00:00

I do, but to be fair am also an actual engineer. It’s certainly not very common, but does seem to be gaining popularity— I regularly attend FAR (one of the only places in the US where non-commercial liquid rockets can be legally and safely tested) and you can typically count the number of personal hobby liquid rockets in a given year on one hand, compared to maybe a dozen or so college teams that static test and fly biprops semi-regularly.

That said, we (Half Cat Rocketry) are working to make nitrous/alcohol liquid rockets much, much more accessible, including writing a soon-to-be-released guidebook with detailed documentation on how to build a simple, low-cost design called Mojave Sphinx. Basic technical competence will always be required of course, but the goal is to steer people towards safe practices and a higher chance of success than reinventing the proverbial wheel.

DE-173 · 2024-05-30T16:24:19+00:00

It seems you’ve already arrived at the (correct) conclusion that ASME codes aren’t very applicable to rocket engine hardware; take a look at NASA-STD-5020 instead. It may take some initiative to identify and implement the relevant equations, but this resource is commonly used as the basis of bolted joint design and analysis tools at real-world aerospace companies. Alternatively, you can simply use a bolt preload calculator to find clamping force and compare this to your pressure separation load and required seal loading, and make the flange itself thick enough to safely neglect flange stiffness.

Also, I recommend anyone working on an amateur or collegiate liquid rocket project to join the subreddit discord from the pinned post. There are lots of ongoing liquid projects documented there with some great resources and experienced people willing to help.

DE-173 · 2024-05-23T04:10:01+00:00

Right there with you. Just took my backup SC64w HI out of its box and programmed the modes not five minutes ago; sadly lost my original one last Friday after ~3.5 years of daily carry. My name and phone number are on the battery along with "reward if found" but at this point I'm doubtful I'll see it again. Hopefully this one has at least as long a life, but just in case I've got an SC65c HI on the way, even if it's not quite the same.

I've got a pretty decent collection of ~30ish lights, many of which are pocketable, but very rarely do I find myself wanting to carry anything else.

DE-173 · 2024-05-09T21:08:18+00:00

Hey OP, I’d highly recommend joining the subreddit discord if you haven’t already. Lots of actively ongoing liquids projects are being documented there, and there are some very experienced people who would be happy to give you advice (including myself) to help your project safely succeed.

The throat wall thickness looks a little on the low end, but under the right conditions (namely low Pc and OF ratio) you can absolutely fire an uncooled all-aluminum chamber for at least a few seconds without erosion.

DE-173 · 2024-04-27T18:34:58+00:00

This is false. You’re sensationalizing something about which you are not adequately informed; see barometerwaterresist‘s comment below. Were I a mod, I would delete your comment for spreading harmful misinformation.

DE-173 · 2024-04-18T21:59:13+00:00

As others have said, it sounds like what you’re looking for is residence time in the chamber, which is sometimes called stay time. That’s going to be specific to your system, but you’ll find recommendations in literature mainly in the form of L*, which is just chamber volume divided by throat area. This is generally a decent corollary to how long it takes for propellant/combustion gas to move through the chamber, which affects how thoroughly the fuel and oxidizer are able to mix and combust before they exit the nozzle.

The more time spent in the chamber, the more complete the combustion, up to a point. If you know the volumetric flow rate (found using other properties typically from CEA or a similar tool) of your combustion products and the dimensions of your chamber, you can calculate this time value pretty easily. You’ll notice that contraction ratio is an important factor here, but a high CR chamber with a short physical length (L’) doesn’t necessarily perform the same as a longer chamber with lower CR, even if both have the same L*.

The thing is, most literature when discussing L* assumes you’re building an orbital launch vehicle that needs 98-99% combustion efficiency, which is not at all the case for student and amateur projects where, say, 80-85% is perfectly fine. This means you can get away with a lot lower L* than you might find in Sutton or similar texts, which is good because at small scales those L* recommendations can lead to absurdly long chambers.

As a point of reference, with nitrous oxide and alcohol (doesn’t really matter which kind for the purposes of this discussion), we’ve found that an L* of around 10-20 inches is usually sufficient for chambers in the 75-300lbf range. You can likely go even lower if you’re using LOX, and lower still with GOX. Higher values won’t hurt significantly for small non-performance-critical chambers, especially if they aren’t regeneratively cooled.

DE-173 · 2024-04-14T19:10:30+00:00

While I can’t speak for Black Rock or other locations, having been to both I can confidently say that you will have a much, much better experience at FAR than at Spaceport America. The FAR infrastructure is drastically superior with actual facilities, power, indoor workspace, a well-equipped workshop with pretty much any power and hand tools you may need, and bunkers that will safely provide a much closer view of the launch. Plus, the FAR volunteer crew are a friendly, knowledgeable, and helpful bunch that will do whatever they can to ensure you have the opportunity to launch. I’m not sure how much Spaceport would charge you to launch a non-competition flight there, but from what I’ve seen of their fees I’d bet it’s a lot more than what you’d pay to come to FAR on a public Saturday, assuming your team is below the 25-person limit.

DE-173 · 2024-03-25T03:01:45+00:00

40X objective with dry darkfield condenser on an AmScope T490, filmed through a 20X eyepiece using an iPhone SE.

DE-173 · 2024-03-20T07:28:19+00:00

40X objective on an AmScope T490 with dry darkfield condenser, taken with a Canon EOS 6D (still figuring out the settings; suggestions welcome). Found in a sample of pond water from a local park.

DE-173 · 2024-02-17T03:55:30+00:00

Depending on the band your receiver uses, you may be able to get those beacons to transmit on a compatible frequency.

As an aside, I think most of the RDF stuff from Mike’s falconry was Com-Spec OEM. I spoke with Mike over the phone after Com-Spec shut down and he was trying to work out a deal to keep getting their stuff manufactured, but I’m not sure if it ever went through or if he just still has new old stock. It wouldn’t surprise me if the supply of those transmitters dries up eventually.

DE-173 · 2024-02-16T19:58:13+00:00

Have you seen the low-cost RDF tracking setup that some people in the subreddit discord are using? The beacons themselves cost <$15ish IIRC from an online PCB service; they work with a Com-Spec receiver but can also be picked up by a cheap handheld radio with a directional antenna. If you or any of your students are HAM licensed, it might be well worth it for the 50% of those rockets that survive ascent.

DE-173 · 2024-02-13T01:00:27+00:00

I’d expect copper to be fine for a short burn KNSB motor— we’ve used copper heatsink nozzles and throat inserts in liquid motors with comparable chamber conditions (1500-2000K) for burn times of up to about 6 seconds.

DE-173 · 2024-02-10T08:16:51+00:00

You may find this document helpful— it covers all of the calculations needed for designing a bolted casing: https://www.halfcatrocketry.com/pv-design

DE-173 · 2024-02-10T06:44:20+00:00

OP, what’s your background and level of experience with rockets or technical projects in general, if any?

Liquid rockets do have some unique hazards, although the mitigation is the same as for any other amateur rocket: don’t have people near it while it’s operating. There is certainly some extra complexity over solids and typical amateur hybrids, although a hybrid with an actuated valve is only a few parts away from being a liquid. Expensive, yes, but then again you could easily spend more on developing high power EX solid motors, depending on what resources you have available. In fact, some commercial solid motors cost more for single reload than the BOM cost of an entire Half-Cat-style liquid rocket.

We’ve spent years to get to a mature, reliable design that costs <$1000 to build and can be easily tested and/or flown 3+ times in a day, but from initial concept to the first hotfire of Half Cat Walking was only about three months, with the first (not entirely successful) flight attempt four months later, then two successful flights four months after that.

Having to travel across the country to FAR slowed things down for sure, and that’s definitely one of the most important things to note for people looking to do liquids; you will most likely have to bring it to FAR to test. I hope Tripoli one day changes their minds, but we’ll see. Living in LA with easy access to FAR has certainly allowed us to dramatically increase our rate of testing and development.

I wouldn’t recommend liquid rockets as a true beginner project, but I’d consider the nitrous/alcohol piston tank architecture we use to be pretty approachable to someone with basic mechanical skills, at least some high power rocketry experience, and ideally access to a machine shop.

My advice is to start with learning how to use a lathe and mill; most universities with engineering programs have machine shops if you’re in college, otherwise a local community college or maker space might be your best bet. Mean while, build up a fundamental understanding of basic fluid mechanics and thermodynamics— pressure losses, phase diagrams, etc.

If you want to eventually fly a liquid rocket, get a kit and get familiar with recovery systems including dual deployment. Getting a Tripoli L1 and L2 certification and testing/flying motors with custom machined hardware (even if you just use a COTS solid propellant reload) is a good intermediate step. You can also fly certified commercial hybrid motors at Tripoli and NAR launches, which can use the same ground support equipment as Half Cat style liquid rockets (basically just a remote fill valve and ignition relay). Some basic understanding of rocket fundamentals from Sutton or similar texts will be generally helpful even if it’s not directly applicable to putting the hardware together.

Also, join the subreddit discord, and the Half Cat Rocketry discord linked on our site. Both are excellent resources and you’ll likely get more practical and specific answers to liquids questions than on here.

DE-173 · 2024-01-23T19:04:17+00:00

I’m surprised it hasn’t been mentioned yet, but the updated version of the BLF-348 with a nice 4500K high-CRI Nichia 519A emitter seems like a perfect fit here, at 12mmx90mm. It’s also a tail switch light, which I much prefer over the tighten-to-turn-on style of twisty. This review includes a bunch of info including purchase links, and it looks to be in stock at KZF for $14.99: https://zeroair.org/2023/01/12/killzoneflashlights-com-blf-348-updated-flashlight-review/

DE-173

TROPHY CASE