The core of the flamethrower mechanism is a a bottle of WD-40 that sprays oil at a lit candle/lighter and acts like a flamethrower. This project is a good combination of rapid prototyping + some basic power electronics.
This project was a joint project with Victor Rodriguez and Candace Chen.
Step 1: Get the Materials!
1. WD-40 Can
A can of WD-40 (get a 12oz can) This should be readily available at your nearby hardware store.
Get a "door-lock actuator", these are linear actuators that sometimes are put on cars to automate the door locking mechanism (they press the button down for you when you hit a button on the driver side). These should be available from Amazon or Ebay, here is an example:
Anything that looks like the above should be fine (they normally run on 12V because that is what the low voltage system of a car runs at).
3. Some hot glue and hot glue sticks (any should work)
4. A piece of hanger wire or welding rod.
5. RC Car from Radioshack
Buy the cheapest RC car from Radioshack (should be about 15 bucks or less)
6.A n-channel mosfet and a diode and a 1k Resistor (these from sparkfun should be fine but you can probably use any power FET + diode you have laying around)
https://www.sparkfun.com/products/10969 (you can probably use any value between 500-10k Ohm so don't feel obliged to buy a pack of resistors.
7. Cardboard, or Acrylic or Sheet metal, anything to make your box enclosure
I used acrylic to laser cut a box for the assembly but you can use anything you want.
8. Tape and/or Acrylic Cement
To fasten your box together.
9.Solder Board or Bread Board
10. Quick-disconnect or any kind of connectors
11. AA Batteries + Battery Holder
12. Candle and a lighter
Step 2: Get the Electronics in Order!
Use the batteries or a power supply at 12V to test the actuator and make sure which connections will make it extend and which connections will make it retract. You want it such that when you activate the actuator it will retract. When you find the right connections make sure to mark them! You'll eventually put connectors at the end of these two lines.
Next is to open up your new RC car and find out where the motors are connected. Disconnect the motors but keep the entire circuitry including the battery holder. The two leads where the motors get connected get 5V applied to them when you hit a button/joystick on the RC remote. We are going to use this 5V signal to drive the MOSFET to drive the actuator. Solder two wires to the pads where the motor was connected and use a multimeter to verify it gets around 5V when you press a button/joystick in the remote.
Lets fill up the battery holder with batteries to create 12V.
Next put a together a control board with the following schematic. The control board will have several connections to the "outside" (actuator, batteries and ex-RC car). I suggest you put quick-disconnect connectors at the end of these lines (like Deans connectors, or headers or spade connectors)
[schematic goes here]
In case you are wondering the resistor is a "pull down" resistor it makes sure that when you are not applying voltage the FET discharges, if you don't put this resistor then your actuator will behave very weirdly. The diode is a flyback diode commonly used when dealing with inductive loads (like solenoids or motors etc). Here is more info: http://en.wikipedia.org/wiki/Flyback_diode
When you are done connecting everything, double check it and then connect it all up and make sure the actuator moves reliably with the remote input.
Step 3: WD-40 Spraying Mechanism
You can tape the actuator to the side of the can. Next use a piece of hanger wire or welding rod to connect the moving part of the actuator to the spray button of the WD-40. You can use hot glue to do this and it works quite well (i'm sure there are better ways of doing it though).
Use your electronics to test if your spraying mechanism actually sprays WD-40 upon command with the RC remote. (don't make a mess!).
Next get a candle and do a test!
[video goes here]
Step 4: Package the Electronics!
Me and my friends used a laser cutter to cut a puzzle box for the actuator. You can make this box out of anything really... (cardboard, wood, sheet metal etc)
This box makes it easy to transport the fire-breathingness everywhere!
Step 5: Test the Fire-breathing!
Other possible uses include pumpkins for halloween, reindeer/santa claus for christmas, etc etc.
Have fun with it but first of all be VERY VERY VERY safe about it. Obviously make sure no one gets sprayed with fire! Safety First!
And after you are done... please share your creation with others! We would love to see what kind of fire-breathing things you come up with!