28th September 2023
Flame gun
Introduction
Recently I've been thinking about how to spice up Tesla coil shows. Other musical shows likes festivals or concerts are using all sorts of visual effects like lasers, LED screens, CO2 jets, flame guns, confetti guns, fireworks, cold spark guns, etc.. From this list I was most interested in flame guns. After checking how pricey (and probably not available to ordinary people) those festival style flame guns are, I quickly decided to build my own. I have discovered one flame gun somewhat cheaper than others on eBay.
img.1. - DMX Fire machine, ebay listing
This flame gun looks well built and it has some industry standard "DMX" control option. Thanks to some Youtubers showing the insides of the machine, I quickly realized how this works and stared on building my own. Building my own has a few advantages, I can build it cheaper, optimized for my needs and you learn much more this way.
vid.1. - DMX Fire machine, YT video
vid.2. - DMX Fire machine, YT video by Bigclive
The working principle behind those is very simple. You simply load a can of either starting liquid or lighter fluid into a holder that is pressed into a normally closed solenoid valve with some springs. After a starting pulse is applied, the solenoid valve opens and the high pressure liquid shoots out of the can. Above the can, high voltage electrodes are placed to arc over and combust the shooting liquid.
img.2. - Starter liquid, springs
img.3. - Can on the spring platform
img.4. - Solenoid valve
I got myself some springs, can of starting liquid and a small solenoid valve. There was a big problem though. I need some reliable way to mount the can into the solenoid valve and this ended up being much harder task than I thought it will be. I have found some M5 nut which I glued to the valve in which I placed some teflon tape to seal the pressure. Looking backwards this was a naive approach. The pressure in the can is quite high (over 100PSI) and the liquid finds even the smallest gaps and leaks. I ended up buying 2 different solenoid valves to see if I can find some way to mount the can in them. Unfortunately I wasn't able to find any solution that would be reliable and most importantly allow for easy can replacement. This is when I settled for a dirt cheap, easy but somewhat inefficient solution; electromagnets.
img.5. - Flame gun construction
img.7. - Flame gun construction
img.6. - Flame gun construction
img.8. - Flame gun construction
On the pictures above you can see I've build a base on which 6 M8 threaded rods are placed which will hold the entire construction together. I've designed a PCB which contains an Arduino Nano which is a brain of this entire machine. The PCB also contains a tiny ZVS driver power supply with a transformer from old CRT TVs. There is also a big 20A bridge rectifier and about 27mF of input capacitance. It is powered from an iron core transformer which delivers about 15V after rectification. During the fire pulse the electromagnets and the ZVS power supply are activated. The electromagnets pull a little bridge between them with a small hole for the liquid to shoot out from.
A very simple mechanism, yet I don't like it as much as the solenoid valve mechanism, since this is quite inefficient. The electromagnets consume about 40W of power just to push the liquid out of the can.
40W is unfortunately just a smaller part of the power consumption since the ZVS driver draws about 100W of power. Funny enough is that I'm using only 50VA transformer for the job! But since the flame gun is running very small duty cycles and the "stand-by" consumption is only about 4W, the transformer does the job well and it only heats up very slightly even after half an hour of operation.
img.9. - Flame gun design
vid.3. - Flame gun first tests
I am quite happy with the first test of the flame gun I designed. It shoots about 1-1.5m long flames. I also equipped the gun with multiple temperature sensors and accelerometers for safety. Temp. sensors are monitoring the temperature of the can and if it reaches too high, the device shuts down. The same goes for the accelerometers which are detecting the angle of the device. You don't really want the device to shoot flames into the audience in case the machine falls down.
The machine really only has 2 problems; The body of the machine is made out of flammable plastic and sometimes some liquid falls back into the machine and ignites. That's why a 120mm fan was placed in the back of the machine to constantly blow air on the top of the can.
Would I mark this as a success? Well that's though to say. Although it was cheaper to build than commercial product, it lacks the build quality. If the flame machines on ebay were slightly cheaper and featured an optical input as mine does, I would probably not choose to DIY this.
img.10. - Flame gun finished
img.11. - Top view (no can loaded)
This was one of the funnier projects, it was relatively quick to build and it works the way I wanted it work. If it wasn't for the struggles with the solenoid valve, it would also be dirt cheap. There is also something amazing about having a huge flame available on a single button push. I'm looking forward for my next Tesla coil show where I can integrate 2 of these flame guns into.