Alright, here it is. The culmination of 8 years of messing with fire in the garage. My third and final (?) pass at a wrist-mounted flamethrower!
This thing is crazy dangerous, and, I cannot stress this enough, crazy fun.
After my last backpack-based version I brought to New York Maker Faire 2014, I had a laundry-list of changes I wanted to make. The whole thing was controlled using a knock-off Arduino Uno with header pins gracefully hot glued into their headers, a perfboard abomination on my forearm for control, and a lead-acid battery (no I’m not kidding) attached to the already heavy aluminum backpack. Oof.
Since then, I’ve learned a tremendous amount more about how to make things, so things get less sketchy from here on out. This version does away with the entire backpack (and yes, the lead acid battery as well), instead favoring an approach where everything is mounted on my right arm. My method for analog gas control gets more reliable, and a custom PCB controls the whole shebang.
After doing some prototyping and testing with gas flow, I started fabricating the exo-skeleton-esque frame to hold all the components. I did all the CAD in Fusion360, sliced the 3D printed parts in Lulzbot Cura, and printed them on a Taz 5 with the stock extruder in Verbatim black PLA.
After I had something to mount everything to, I started work on the PCB. The board had to control the servo for analog gas control, the solenoid valve, the taser for ignition, read inputs from the control switch on my hand, plus an OLED and a few buttons for mode selection. I went with a Atmel 32u4 for the Arduino IDE compatibility, relatively low cost, and native USB support.
The result is beyond satisfying. And bringing this crazy thing to New York Maker Faire 2018 was even more so. The NYC Fire Marshals responsible for making sure I didn’t kill anyone or myself were beyond cool. Thanks Bob and Rob!
Not sure if I’ll ever dive back into the flamethrower game, but if I do, I’ll probably make a custom tank so I can dump the whole thing at once for a HUGE burst, and redo the palm piece. I might replace the taser for some nichrome wire or a pilot light as the taser was fairly unreliable.
This model of the flamethrower is controlled with an Arduino microcontroller, unlike the previous model that was completely mechanical. This version has a forearm component and a backpack component. The backpack has a propane tank mounted to it, and gas flow is controlled with a servo-actuated pinch valve.
The onboard Arduino knows how much gas to release based on the position of a linear potentiometer. The potentiometer is mounted on the inner wrist of the gauntlet. When the hand is pulled back, the slide potentiometer slides position. The resulting analog signal is then sent to an Arduino analog pin. Based on this signal, the Arduino changes the position of the servo. When the servo spins, it pulls down on a 3D printed part that pinches the fuel tube, allowing different amounts of gas to flow.
There is also a modified taser incorporated in this version that is used for ignition. The 5v battery pack and voltage increasing circuit are mounted on the back panel of the flamethrower. Because the Arduino can’t source enough current to run the taser on its own, a digital pin on it has been allocated to activate a relay that connects the dedicated battery to the taser circuit. From there, the two wires that have the high voltage are run up my arm and into the hand piece so that they may ignite the propane.
Above is a schematic of the basic electronics of the flamethrower. All of the inputs and outputs are connected to the Arduino, and the specific pins they are connected to are indicated in the schematic.
This is how the gas flow is controlled. The tubing is wedged between the two 3D printed parts connected by a hinge, and the servo pulls one end of the top part down, pinching the tubing off to varying degrees.
Here, all of the components can be seen attached to the aluminum backing.