Embedded Files
I set out to build what I believed could be the world’s smallest wrist-mounted, and most importantly, functional flamethrower. The journey was long but rewarding. I began the design at the end of my freshman year and reached a satisfactory version about a year later.
Integrating flammable pressurized gas into a 3D-printed mechanism that releases pressure at a controlled rate and along a specific trajectory, while igniting reliably and keeping both the user and the device safe, turned out to be a complex challenge.
First "Functional" Model
It started with the first “functional” prototype, which I put together in about a month. It used a miniature one-way valve for gaseous or liquid butane, manual ignition with a lighter, and a rough throttling system. A spring-loaded cylinder holder kept a tight seal between the valve and the cylinder outlet and also helped with throttling. The main drawbacks were gas and flame leakage at the valve, a time-consuming equipping process that used strings, a bulky and uncomfortable design, and an unreliable throttling and loading mechanism.
Forearm Molded Design
The next major model followed the shape of my forearm and combined elements from the previous version. In theory that shape should have been sturdy, but it limited my range of motion. I upgraded the ignition to a manual switch that triggered an electric arc, but the old nozzle assembly remained and still leaked.
First One-string Automated Design
In the following iteration I designed a custom momentary switch that latched onto the throttling string and actuated the electric discharge. This was the first version to automate all processes. The nozzle assembly used a TPU-printed interface and an ASA plus alumina high-voltage electrode holder. I tuned the throttling system with custom springs to deliver the force I wanted. The main problems were inconsistent arc timing and occasional jams at the cylinder nozzle.
Fine Ignition Initiation Timing
By changing how the arc was actuated, I could control exactly when it started, either before gas exhaust or during it. For safety I set the arc to start well before gas release. That helps prevent any buildup of flammable gas and gives a clear visual “armed and ready” cue.
Nozzle Assembly
The TPU and gas-cylinder valve interface went through the most iterations, since it is critical to safe operation. The internal geometry had to be snug enough to prevent pressurized gas from leaking at the sides, but loose enough to allow quick cylinder changes. It also needed to withstand about 150 N (1.5 kg) of force during full-throttle operation. During use, decompression chills the nozzle assembly and the TPU interface, which causes thermal contraction and loss of elasticity, so I factored that in as well.
Another issue was frosting along the path to the nozzle. That increased liquid carryover, reduced throttle control, and hurt safety and reliability. To improve heat transfer, I built an all-copper heatsink with a series of small-diameter tubes to increase thermal mass and surface area, which improved cooling of the surrounding air.
To maximize flame length, I aimed for flow that was as laminar as possible at this scale. I mostly used repurposed brass 3D-printer nozzles with a nominal 0.4 mm tip ID, then ground and re-drilled the internal cavity to tune the cross-section in pursuit of longer range.
The Current Version
The current version brings together the best iterations of each subassembly in a compact, safety-focused housing. A main kill switch cuts power to the entire system to prevent accidental ignition. The arm mount uses two adjustable Velcro straps and a thin foam pad for comfort. A single control string, connected to a ring on my finger, starts the electric-arc ignition with a light tug and gradually opens the cylinder valve as I pull harder.
Photo Gallery
What I Learned
Laminar flow optimization
Imbedded electronics
Compact design
Material compatibility
Mechanical automation
Heat transfer optimization
Future Work
Changing the high voltage generator module to produce higher frequency, higher voltage discharge which should be more resilient toward strong winds.
Experimenting with a series of custom SS nozzle assemblies aimed at achieving "true laminar flow".
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