Rocket Launcher With PET Bottle

The goal of this project is to build a cheap paper rocket launcher.

We will use a PET bottle of 1.5 liter of sparkling beverages such as Coca-Cola or Pepsi Cola. This is because a bottle for sparkling beverages can withstand much higher pressure than a bottle for still beverages.

1 x 1,5 liter PET bottle

1x adapter 1/2" to PET bottle (3D-printed)

1 x electro-valve (1/2", power supply 12 Volt )

1 x pvc 90 elbow

1 x adapter 1/2" (external thread) to 20 mm

2 x pvc tube diameter 20 mm - length 35 cm

1x wooden launch platform

1x pvc tube diameter 20mm - length 15 cm

1x 9V - battery holder

1x push button

1x adapter push button

1x cable adapter - fire handle

1x 2-wire cable - length 2 m (2 x 0.75 mm2)

1x 9V - battery

1 x red electrical wire of 8 cm (0.75 mm2)

2 x crimp spade terminal

cable straps

sticky tape

paper

decoration material

pvc glue

wood glue

Teflon tape

The basis for the launch platform is made out of 6 mm multiply wood.

It consist of 4 parts that need to be glued together with wood glue.

A DXF-file is attached which can be used to cut the wooden parts. If needed, we can also supply a DIY-kit with all the required parts.

The thread on the PET bottle is different from the thread on the pvc elbow or the electrovalve.

To be able to connect the PET bottle to the electrovalve, an adapter is needed. This adapter can be 3D-printed with the provided STL-file. Material: PLA, infill 50%.

The fire handle requires 2 adapters, one to fix the push button on the fire handle, and one adapter to guide the electrical wires through the fire handle. These adapters can be 3D-printed with the provided STL-files. Material: TPU, infill 10%.

We will place a small valve in the bottom of the PET bottle. This valve can be purchased at the local car/tyre shop. It is also available in our DIY-kit.

First, we will drill a small hole in the bottom of the bottle with a diameter of 3 mm. Then we will make the whole bigger by using a drill of 8 mm. Finally, we will use a drill of 10 mm. If there are any burrs, remove them with a cutter.

Next step is to insert the valve into the hole. The valve contains : 2 nuts, 1metal washer, and 2 rubber washers. Remove the 2 nuts, 1 metal washer and only 1 rubber washer from the valve. Keep one rubber washer on the valve. Now you can insert the valve with one rubber washer into the hole in the bottom of the bottle. This needs to be done from the inside to the outside of the bottle. This becomes an easy task when you put a stiff metal wire in the valve, to guide the valve through the bottle.

Now put the second rubber washer, the metal washer and one nut back on the valve. Tighten the nut.

Put the second nut on the valve and turn both nuts against each other. Use two wrenches.

Next step is to install the electrovalve.

Put some Teflon tape around the 1/2" threads of the electrovalve. Be sure to wind it in the correct direction = clockwise.

Also put a good amount of Teflon tape around the thread of the PET bottle.

Screw the PET bottle into the 3D-printed adapter as far as possible. Next screw the electrovalve into the other side of the 3D-printed adapter as far as possible. Be careful to screw the inlet side of the electrovalve into the adapter. The inlet side of the electrovalve can be recognized by the presence of a filter. Also on the backside of the electrovalve an arrow indicates the direction of the flow: inlet to outlet.

Before we continue we will test if the set is airtight.

We will use a small bicycle pump with pressure indicator. We will inflate the PET bottle with 2 Bar (= 29 PSI).

Check if all connections are airtight. If not, try to screw the bottle or the electrovalve a little harder and check again.

If still not airtight, unscrew the leaking component and put more Teflon tape to make it airtight.

Glue the 1/2 inch adapter onto the 'PVC tube diameter 20 mm - length 35 cm' (i.e. launch tube) with some PVC glue.

Put the 90 degrees elbow on the outlet of the electro valve.

Glue all the wooden parts together with wood glue as shown in the picture. Wait until the glue is dry.

Then place the PET bottle in the wooden holder and use some straps to fix the neck of the bottle to the wooden holder.

Also use some straps to fix the electrovalve to the wooden holder as shown in the picture.

In this step, we will make the fire handle of the rocket launcher.

First, we will make the red wire of the 9V-battery holder longer. Therefore, solder the red electrical wire of 8 cm to the red wire of the 9V- battery holder. Use some isolation tape to protect this soldering or use some heat shrink tubing.

Put the push button in the 3D-printed adaptor. Only one of the adapters will fit. And make sure that the 'collar' of the adapter is in the right direction as in the figure.

Remove the cable jacket of the 2-wire cable of 2 m for about 15 cm. Secondly, strip the 2 wires.

Now, we will solder one wire of the 2-wire cable to the black wire of the 9V-battery holder. Use some isolation tape to protect this connection or use some heat shrink tubing.

Put the wires of the 9V-battery holder together with the 2-wire cable through the second 3D-printer adapter. Note that the adaptor has a 'collar' on one side. Make sure to use the adapter in the right direction. The collar needs to be on the side of the 9V-battery holder as shown in the picture.Make sure that the 2 free wires are long enough and come out of the PVC tube.Use a cable strap to keep the cables in place just below the adapter as shown in the picture.

Push the wires through the PVC tube diameter 20mm - length 15 cm (i.e. the fire handle) so that the red wire of the 9V- battery holder and the second wire of the 2-wire cable come out at the other side of the fire handle, as shown in the picture. Now push the adapter in the fire handle so that the tube is closed at that side, as shown in the picture.

Solder the red wire of the 9V-battery holder and the remaining wire of the 2-wire cable to the push button.

Now we can push the push button with the adapter in the fire handle.

Glue the 9 V-battery holder on the PVC tube diameter 20mm - length 15 cm.

In this step, we will connect the fire handle to the launcher.

Therefore, remove 5cm of the cable jacket of the 2-wire cable coming out of the fire handle.

Strip the 2 wires and connect a crimp spade terminal on both wires.

You can now connect the fire handle tot the electrovalve as shown in the figure.

Use some straps to secure the cable.

Now we will make a paper rocket.

First put some sticky tape around the remaining PVC tube of diameter 20 mm and length 35 cm.This will make the paper rocket a little bit bigger in diameter then the launch tube.

Next wrap a sheet of paper around this tube and put sticky tape on it so that you obtain a paper roll. The most important thing to do, is to make your paper roll airtight at one side. Use some sticky tape to do this.

Now you can start decorating your rocket by adding a nose cone, boosters,... Use your creativity to make a nice paper rocket.

Place your rocket launcher on a flat surface.

Put your paper rocket over the launch tube.

Use the bicycle pump to put 2 bar ( 29 psi ) of air into the PET bottle. Do not exceed this value.

Countdown 3 - 2 - 1 and press the fire button!

Try different types of rockets, try some wings, put some extra weight, change the angle of the launch tube (45 degrees, 30 degrees, 60 degrees and see how far your rocket can fly.

Have fun!