Making World's Smallest Potato Cannon

In this video I will show you how to make a Mini Potato Cannon.

#potatocannon #minicannon#cannon
0:00 Intro
0:05 Design
0:20 Combustion chamber
1:51 First test
2:14 Fuel Chamber
2:42 Air Pump
3:35 Assembly
4;30 Final test
5:03 Outro
5:25 Thanks

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Hello and welcome to another video. In this video we are going to make a mini potato cannon. In a potato cannon projectile is loaded from the front and air pressure or combustion of a flammable gas is used to launch projectiles at high speeds. Here I am going to use butane as fuel. A spark ignites the fuel and fires the projectile. My plan is to use a glass tube for the chamber so that I can see the combustion. I will be cutting a glass tube from an old Kjeldahl flask. I made this 3D printed jig for cutting glass. On the bottom we have two rollers to support the tube. And on the top a Stanly roller glass cutter is fixed on a 3D printed part. Two stainless steel rods are used to guide it. Length of the glass being cut can be adjusted by moving the stopper at the end. Once everything is tightened pressure is applied from the top and glass is rotated to score it. Ends can be wet sanded to finish it. I have started with 80 grit and finished with a 220-grit sandpaper. Barrel is made from a pen body. Closing end of the chamber and the part joining the chamber and the barrel are 3D printed in ABS. I will glue the end plug of the pen to the ABS part so that I can remove the barrel if needed. All the parts are glued with CA glue. Since the combustion is only momentarily it won't affect the 3D printed parts and the plastic barrel.
Too little or too much fuel won't give a proper combustion. In this case it has to be 1:15.6. So, I have to find a precise way to supply fuel to the combustion chamber. My plan is to use a cylinder filled with fuel. And by moving the piston a measured length I can supply a precise amount of fuel. Cylinder is made from an aluminum tube and the piston is made from an O-ring sandwiched between two plastic rings. End caps are 3D printed and glued with epoxy. A little silicone grease inside the tube will give better seal and reduce friction. After firing the ambient air will rush into the chamber but that is not enough for the succeeding firing. So, I have to find some way to supply more air into the chamber. My idea is to make a pump from a glass syringe. I have cut the syringe barrel and plunger to the correct size using the glass cutter. A hole is drilled on the bottom of the plunger using a diamond bit for the air to enter. Also, I have to make a one-way valve. I am using the rubber valve material from a 3M mask to make a one-way valve. Valve material is attached to a 3D printed part and inserted into the plunger. When the plunger is pushed forward, a one-way valve opens and lets air into the pump. Most of the air enters through the valve since the other side is a restricted flow path. And when the plunger is pushed back the valve closes and the air is pushed into the chamber. Now we need a body to hold all these components together. Body is split into different parts and printed on ABS. First, I am fixing the piezo igniter from the lighter. Handle is made from a 3D printed part and two stainless steel tubes. All parts are glued with CA glue. Part holding the combustion chamber is made as small as possible so that it won't block our view. I am using a stainless-steel needle for connecting the pump and the combustion chamber. Needle will be work hardened by extrusion so it is annealed by heating and bent to form the connection. My first plan was to use paper clips to make the high voltage connection from the piezo igniter. But I was having a high voltage leak, so I used copper wire covered with a thick tube as the conductor. Ends of the wires are connected to the terminals of the piezo igniter and a spark gap of five millimeters is kept inside the combustion chamber. A small stainless-steel tube is bent to make connection between the fuel cylinder and combustion chamber. Connections are press fitted so that I can remove it to refill the fuel cylinder. I am filling the fuel cylinder with butane from a lighter. As per my testing I have to supply two milliliters of gas for a single shot. Now everything is ready First the pump is used to fill the chamber with air.
I am using a pipe to cut the potato to the exact diameter. Projectile is loaded into the barrel. Finally, the piston is moved marked length to supply fuel, it can hold fuel for ten shots. Now we just have to press the piezo igniter.