This instructable is done for the completion of the final deliverable for the FALL 2014 MAKE course. (www.makecourse.com)
By: John Pierce
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Step 1: Getting Started
In the beginning god created Auto CAD.
I first drafted the parts that I needed in Auto CAD.
I have attached the full assembly and all of my custom parts that i designed.
I have also included the .stl for 3D printing
Step 2: The Plan
The idea behind the auto cannon is have a cannon that can locate a target and fire upon it. How exactly are we going to be doing this one might ask?
Well here's the answer
The plan is use a ping sensor attached to a servo so it can move back and forth. For those of you who don't know what a ping sensor is its a echo location device. Meaning that it send out a wave, this being the ping, and listens for the echo. With a little bit of math and knowing the speed of sound you are now able to tell how far away an object is.
Servos.... servos are basically motors with a limited range of motion. they can also be told where to go. This comes in handy later on in the project.
WHATS Actually happening.
The ping servo goes to angle one and the ping sensor then sends out a ping and listens for the return.
If the ping sensor doesn't find an object inside the specified range then it proceeds on to the next angle
If it finds an object inside the specified range, it checks again to make sure its not an error and if the object is still present then it tells the cannon servo to go to angle one and fire in that direction
Step 3: The Wave of the Future: 3D Printing
Three dimensional printing has changed the world for inventors. You can have custom built pieces that you designed in a matter of hours and for significantly less money. It takes an .stl file and prints in plastic.
Step 4: Arduinos
The Arduino is arguably the biggest advancement for inventors. The Arduino is microcontoller that is easily programmable and easy to write in. This provides easy inputs and outputs that can be easily defined and implemented.
I had to write a custom library for this project. It controls the sonar functions. I have included said library as well as the Arduino sketch.
You must add the library to you Arduino libraries.
For those of you who don't know how to do that here is a link on how to do it.
Step 5: The Cannon
Getting this cannon to fire was arguably one of the hardest parts of this project.
First I tried firework, but this did not work at all do to the lack of gunpowder in the fireworks I bought.
So then I bought shotgun shells and took them apart. The gunpowder in the shells was very course so it did not ignite very well, providing a less than spectacular shot. After doing a little bit of research I found that adding a few cap gun caps would provide a more energetic shot. This proved to be true, when i added 8 caps and a pea sized amount of gun powder.
While not being lethal it does hurt a significant amount. As one of my brothers found out.... Thank you Alberto.
Step 6: The Assembly
First thing that is needed is a board that is cut to the same size as the top of the box.
Then you needed to cut 4 pieces of threaded rod, also know as ALL Thread.
Next you need to cut holes for the servos where the horn will be on the center line of the box. The hole needs to be in the same place on the top of the box and board.
Then you need to 4 drill holes in the top of the box and the board. These are for the bolts.
Next you bolt the two pieces together, forming the upper assembly.
After that you mount the servos in the board and box top.
Step 7: The Wiring
The wiring for this project is pretty straight forward.
Servos need a 5v, signal, and a ground. The signal is what controls the servo and the 5v and ground power the servo. the servos are connected to 10 and 11 pins on the arduino.
The ping sensor required 4 wires. A 5v, ground, echo pin, and trigger pin. The trigger pin and echo pin are connected to the arduino pins 8 and 9 respectively.
The hardest part of the wiring was the ignitor. It requires an 2n222 npn transistor. The base of the transistor is tied to pin 13 of the arduino, the collector is tied to 5v through the ignitor and emitter is tied to ground. Over all still straight forward.
Step 8: The Ignitor
The ignitor was a problematic portion of this project. I was originally using model rocket ignitors but the were relatively expensive in comparison to the amount you get. While my roommate and I were putting up Christmas lights at our apartment i had an epiphany. Christmas lights work on a similar principle as the model rocket ignitors. They are also significantly cheaper on account that they come 100 to a pack for $2.50 American. All you have to do is break the bulb off leaving the exposed filament and apply power.
Step 9: The End Result
The final project leads to a cannon that is able to find a target inside a range a fires upon it.