Wrist Mounted Flamethrower

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!

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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.

Old Versions


While on StumbleUpon, I came across a video of a man named Everett Bradford who built a flamethrower to go along with his Halloween costume of the super-villain Pyro. As soon as I saw this, I began drawing sketches, ordering parts, and began building a prototype just to see if it was even possible.

Basically, Everett’s design consists of a main fuel canister on the inner wrist. When the hand is bent backwards, a control line pulls down on the nozzle, releasing fuel. A tube is attached to the nozzle and the butane is carried to the palm piece, where the fuel is expelled through a brass nozzle. On the side of the forearm, there is a jet lighter which has had the fuel line and the two wires coming from a piezo-electric igniter extended to the palm piece. The jet lighter flame is angled over the main fuel line so that the butane will ignite when the jet lighter is on. What follows are all the versions of my take on Everett Bradford’s design.

Version 1.0

My first version. This was crudely built out of a modified wrist guard, the cap to a medicine bottle, some hemp cord, a butane canister, and duct tape. This version never produced more than about six inches of flame, due to the fact that it would put itself out if the butane gas was coming out too fast. The palm piece didn’t fit right, and required my hand to be in an awkward position for any fuel to come out. However, this first version showed me that it was possible to achieve flame, and that it could be improved to get a more favorable result.

Revision Notes:

  • Modify palm piece so it is comfortable to wear
  • Find a safer material for the palm piece
  • Refine gas release system
  • Allow gas canisters to be removed and replaced easily

WMFT v1.0

Version 2.0

A few major revisions were made between versions 1.0 and 2.0. The medicine cap palm piece was the first aspect to go. It was replaced with a custom made piece, consisting of three layers. The bottommost layer was a piece of plastic taken from the lid of a peanut jar. Mounted on that was a layer of heat-resistant circuit board, then a layer of sheet metal. Three holes were drilled in the piece; one in the middle for the main fuel line to pass through, and two others at opposite ends of the piece for attaching control lines.

This version also included the ability to replace empty butane canisters easily. I took a soda can and cut the top and bottom off, leaving me with a rectangle of thin metal. I then curled this into a circle with the same circumference as the canister, and duct taped it in place. Now butane cans can easily slip in and out of this metal sleeve.

However, there were still a few problems with this design. First, if I released too much butane, it would begin to come out in droplets because of it’s rapid decompression, leaving me with burning drops of butane all over my hand. Also, the flamethrower had to be lit from an external source, such as a lighter.

Revision Notes:

  • Find a way to keep butane droplets from lighting/landing on my hand
  • Build an integrated ignition system to prevent the fire from going out
  • Continue to refine gas release system

 

v2.0

v2.0

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v2.0


Version 2.1

There were very few changes between versions 2.0 and 2.1. Aside from minor adjustments to the paperclip that releases gas from the nozzle, the only other change was an aluminum foil hand guard that strapped onto my hand.

Revision Notes:

  • Find a way to keep butane droplets from lighting/landing on my hand
  • Build an integrated ignition system to prevent the fire from going out
  • Continue to refine gas release system


Version 2.2

In Version 2.2, all components were removed from the modified wrist guard, then reattached with greater accuracy. However, the wrist guard holding the entire assembly to my arm could not be tighened enough to keep it in place when the control lines were pulled.

Revision Notes:

  • Find a way to keep butane droplets from lighting/landing on my hand
  • Build an integrated igntion system to prevent the fire from going out
  • Continue to refine gas release system
  • Keep modified wrist guard from sliding down my forearm when it is pulled forward

Version 2.3

Version 2.3 has a new aluminum foil palm piece cover to keep the hot glue from melting, and an added arm band to help keep the modified wrist guard in place when the control lines are pulled and gas is released from the canister. However, this method did not only fail to work well, but also restricted my movement a great deal. Also, everything attached to the wrist guard was removed and reattached with better placement.

Revision notes

  • Find a way to keep butane droplets from lighting/landing on my hand
  • Keep the modified wrist guard from sliding down my forearm without restricting movement
  • Build an integrated ignition system to keep the flame from going out
  • Continue to refine gas release system

v2.3

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Version 3.0

In this version the arm band was removed. No variation of that idea could give me the stability I wanted and mobility as well. Instead I moved the wrist guard so that the end of it sat right where my wrist is. The size difference between my forearm and my hand held the flamethrower firmly. Then I moved the canister slot accordingly. With these modifications, I didn’t have to worry about the entire assembly sliding down my arm, keeping me from releasing gas.

Revision Notes:

  • Develop integrated ignition system
  • Find a way to keep decompressing butane from landing on my hand
  • Continue to refine gas release system

Version 4.0

The major advancement in Version 4.0 was the addition of the jet lighter ignition system. The first thing I did was took the jet lighter apart and extended the fuel line and positive and negitave ends of the piezo electric igniter so that they would reach the palm piece. After the lighter was put back together, I mounted the torch nozzle and the two wires on a piece of wood attached to the palm piece. Now, when I turned the jet lighter on (still manually at this point), I did not have to light the main fuel externally. The gas lighted immediately due to the jet lighter. However, I was still having quite a few problems with droplets of butane lighting and landing on my hand. Also, I needed to find a way to light the jet lighter without the help of my other hand.
Revision Notes:

  • Find a way to prevent butane droplets from landing on my hand
  • Find a way to ignite the jet lighter with only wrist motion

v4.0

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Version 4.1

Minor changes were made between versions 4.0 and 4.1. Assorted components were adjusted, the pilot light mounting was readjusted, and all tubing connections reinforced. I also came to the conclusion that my troubles with catching myself on fire had to do with the quality of butane I was using.

Revision Notes:

  • Continue to refine main fuel release system
  • Find a higher quality brand of butane canisters
  • Find a way to ignite the pilot light with one hand


Version 4.2

The main change between version 4.1 and version 4.1 was the removal of the pilot light. The electrical connection was faulty, and would short out occasionally. The pilot light assembly needs to be reassembled. Secondly, a larger gas nozzle was used for this version. This allows a much larger amount of gas to come out at once, meaning a much larger flame, and a flame that does not put itself out. Although it currently needs to be lit externally, the result is much more impressive in this version than the last.

Revision Notes:

  • Begin plans for a second device for my other hand
  • Find a higher quality brand of butane canisters
  • Rewire and reattach the pilot light assembly


Version 5.0

This is the final version of this model of the flamethrower. I completely started from scratch when building this version. The modified wrist guard was thrown out, and replaced with a baseplate of sheet metal and straps from an old backpack. The holster that contains the butane canister was instead made from a bent piece of sheet metal welded onto the baseplate, as opposed to scraps from an aluminum can. A swing arm was welded onto the the side of the holster that depresses the nozzle of the fuel canister, releasing gas. A piece of paracord travels through two steel loops welded to the baseplate and connects to the far end of the swing arm. The other piece of paracord is connected to the palm piece, allowing the amount of fuel released to be controlled by wrist movement. Lastly, a piece of clear plastic tubing goes from the butane canister nozzle to the underside of the palm piece, and up into the spout of the flamethrower.

Revision Notes:

  • None – Final Version


Model 2

Version 1.0

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.

flamethrower

 

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.

gauntlet

 

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.

wmftm2_wiring

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.

pinchvalve

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.

backpack

Here, all of the components can be seen attached to the aluminum backing.

 

flamethrowerdemo

Press

MAKE: Live Feed Demo

 

Hackaday Article

 

Popular Mechanics

 

Gadgetify Article

 

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