In this Instructable I will show you how to build a flamethrower from inexpensive materials found in your local hardware store and hobby shop. With a very simple frame made from 15x15 square wood, brass tubing as the exhaust pipe and a powerful servo to activate the butane flask, makes this device very reliable due to minimal number of parts. The servo and igniton source is then controlled by a controller powered from a small battery, and a receiver bound to a transmitter your inputs will control the device from a distance up to 1 kilometer!
Step 1: Materials
The estimate cost for this project is around 40$ and most hardware can be found in your local home electronic store, also hardware shops.Here's all the parts you'll need:
- Ignition system (see Instructable below)
- 15x15 square wood
- Butane flask
- Screws, rubber bands, etc.
- Battery eliminator circuit (http://www.ebay.com/itm/Hobbywing-3A-RC-UBEC-5V-6V...)
- Servo (http://www.ebay.com/itm/High-Speed-3kg-cm-Torque-S...)
Before you can start building your remote controlled flamethrower you need an ignition system. This Instructable will give you detailed instructions of how to build one: https://www.instructables.com/id/Remote-Control-Ign..
Step 2: Frame
We need a frame for which the butane flask can rest, and mount the servo to dispense the fuel upon our command. With a 300ml container of butane I made a frame from 15x15 square wood. I cut 2 pieces with a length of 220mm, these will be the directional bars. 2 pieces, 40mm each, is the crossing bars. However, the crossbars length depends on the diameter of the butane flask.
Once the frame is assembled, using either screws or glue, you'll need a piece of wood as shown in picture number 3. The dimension to take in account is the thickness (depth). You want it to be thick as we will rely on the brass tubing to fit in there by friction. Also this chunk of wood can be glued in place, I always use hot glue.
Step 3: Servo and Dispensing System
Begin with drilling a hole smaller (<1mm) than the brass tubing. For example, if your brass tube has an outer diameter of 4mm, you should drill a 3mm hole. This will ensure we have tight fit, which is important for a functional dispension of the butane.
Increase the inner diameter to match the diameter of your butane adapter, only a few millimeters is fine. Push the brass tubing through the chunk of wood and insert the flask. It should be a snug fit between the brass tube and adapter, if too much of a gap you will experience a lot of butane leakage. You can use tape to reinforce/seal the gap if you find yourself in that situation.
The most important purchase you will have to make is the servo. Don't cheap out buying a 9g servo, it won't work! You need the strength only the higher >30g servos can achieve. I use a super powerful Traxxas 45g servo with almost 10kg of strength, even though it might be a little overkill you should follow my advice and get a stronger servo than you might realize.
Don't use hot glue for the servo as it will break easily due to the high force from the servo. For the push rod I used a nail, and I highly recommend using a steel rod with no flexibility. Make a Z-bend in one end and make it a tight fit through the servo horn. With that done your last step regarding the servo and dispensing system will be to lock it down with zip ties or rubber bands.
Step 4: Electronics and Ignition System
If you haven't made the ignition system yet, now is the time! Follow this video and come back to this step when're done:
I assume by this point you have a working ignition system, great, now we are going to add a component. The BEC, also called battery eliminator circuit, will protect the electric speed controller (ESC) from overwork. Usually the ESC is perfectly capable of providing the servo with power. However, since we are using a much larger servo than usual with a peak current of 2amps, we have to install the BEC to handle the current. The ESC can only manage a current of 1amp, compared to 5amps for the BEC.
Connect the BEC (+ and -) to the corresponding wires from the ESC. Remember to always make a solid solder joint and use shrink tubing! The BEC connects to the port named "Batt" on the receiver, the ESC to the throttle port and the servo to the steering port.
Connect the battery and make sure that when applying throttle the kanthal wire heats up properly, and the servo pushes the butane tank so butane is dispensed. Use a cable tie to hook the heating element in front of the exhaust.
You are now done, let's go out and test it!
Step 5: First Test
First test was a success! The heating element reached very high tempereature very quickly, even though it was only a couple of degrees outisde! Once the ignition wire is glowing red I make the servo push the butane flask forward in order to dispense fuel, once the fuel hits the heating element it ignites. Once it ignites you can turn of the heating element and the butane will "self-ignite".
If you wish to make the flame smaller you can adjust this by squishing the brass tube, this will limit the amount of fuel, and therefore make the flame smaller.
A tank contained with 300ml butane will last for about 30 seconds, with a pipe fully dilated. If you limit the fuel consumption it will last longer.
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