Step 1: Collect the Materials
You'll need to purchase the following parts to get started:
- 2 five foot pieces of 1/2" PVC pipe
- 4 PVC 1/2" 90 degree elbows
- 2 PVC 1/2" T fittings - all solvent weld joints
- 2 PVC 1/2" T fittings - base of T is threaded, 2 ends are solvent weld
- 1 PVC 1/2" cap
- 1 PVC 1/2" threaded male adapter
- 1 PVC 1/2" coupling (optional)
- 1 pipe clamp, 1-1/4" minimum
- 1 standard valve stem
- 15 cable ties - 6" length
- Teflon pipe sealing tape
- PVC cement (may also require PVC primer, depending on cement type)
- soda bottles for launching (2 liter bottles work well, most 1 liter will also work)
- small candle, and a means by which to ignite it
- 2 - 6 rubber bands, ponytail holders, or the like
- 2 #6 machine screws 1" or longer
- 2 #6 flat washers and nuts (optional)
- 3D printed latching mechanism (4 pieces) from my Kickstarter, again HERE or HERE
- 20 - 30 feet of heavy synthetic cord (such as mason's twine)
Step 2: Gather Tools
You'll also need:
- hacksaw, or miter saw
- drill bit - 37/64" preferred, but 9/16" will work, and 1/2" in a pinch
- channel lock pliers (or gloves and a strong grip)
- rubber headed mallet
Step 3: Start Assembling the Base
Create 2 identical T assemblies for the base. You need:
- 6 pieces of pipe, cut to 9"
- 2 T connectors, both of which have 3 solvent weld connections
- Apply PVC cement to one opening of a T connector, and then to one end of a 9" piece of pipe. Press the two glued pieces together with a slight twisting motion. Be sure the pipe is fully seated into the T connector by tapping it with the mallet.
- Continue assembly by gluing the remaining 5 pieces into the other openings of the 2 T connectors as in step 1.
Step 4: Complete the Base
Complete assembling the base of the launcher. For this step, you'll need:
- 1 T connector, which has 3 solvent weld connections
- 1 T connector, which has a threaded base connection, and 2 solvent weld connections on the "ears"
- 2 pieces of pipe, cut to 9"
- 4 elbows
- EITHER one piece of pipe, cut to 19 1/4" OR 2 pieces of pipe cut to 9 3/8" plus the coupler. It is simpler to use the single longer piece of pipe, but you may need to couple shorter pieces, depending on how you have cut up your pipe so far. Make certain to reserve one section of pipe 18" to 22" long for the launcher tube in a later step. The launcher tube must be constructed of a single length of pipe, with no couplers.
- Glue the T connector with the threaded base to the sub-assemblies from the last step, forming a capital "H". The "bases" of the T sub-assemblies should be inserted into the "ears" of the T fitting. Once glued, make sure that both sub-assemblies lie flat (check it on the floor or a table) and that the threaded port of the T connector is pointing directly up. This will ensure that your rockets will be launched directly skyward. For future reference, we'll call this the "H" assembly.
- Glue one elbow onto each of the remaining 9" pieces of pipe. Glue the other end of each piece of pipe into the "ears" of the remaining T connector with the 3 solvent weld ports. Once glued, make sure that the elbows lie flat, while the base (unthreaded) port of the T connector is pointing directly up. This port will become the air fill port, in later steps.
- Glue the two elbows into the two lower legs of the "H" assembly. Work quickly, ensuring that the entire assembly lies flat once assembled.
- Complete the upper legs of the "H" assembly with the remaining 2 elbows, and EITHER one 19 1/4" piece of pipe, OR two 9 3/8" pieces of pipe and the coupler.
Step 5: Build the Launch Tube
Build the vertical launch tube and latch that holds the rocket in place. For this step, you'll need:
- 1/2" PVC male threaded adapter
- 18" to 22" section of 1/2" PVC pipe
- 1-1/4" hose clamp
- 10 to 15 cable ties, 6" long
- electrical or other tape (helpful, but not necessary)
- small candle
- 1 2-liter soda bottle for test fits
- Teflon pipe tape
- Light the candle, and allow it to pre-heat.
- Mark a line around the perimeter of the 1/2" pipe, 11" from one end.
- Hold the pipe over the candle, and gently heat the line you just marked. Continuously rotate the pipe, "rotisserie style" so that it doesn't scorch or burn. Continue heating until you feel the pipe start to bend, which means that the area has softened.
- Remove the pipe from the heat, and compress the length of the pipe, forcing the heated section to gently bulge outwards. Only a slight bulge is necessary - aim for an increase in diameter of 1/32" to 1/16". Sight down the center of the pipe and ensure that you have not introduced a bend. Allow the pipe to cool until it has hardened.
- Test the fit of this tapered bulge by inserting the 11" section into a 2 liter bottle. The opening of the bottle should gently jam against the bulge such that the tip of the pipe is about 1" from the inside bottom of the bottle. This arrangement will allow air to pass into the bottle, but prevent the backflow of water. The jam of the taper against the bottle opening will prevent the water from leaking from the rocket. Make any necessary adjustments by repeating steps 3-5 above.
- With the bottle in place, arrange the cable ties such that the heads latch into the rim around the neck of the bottle. Temporarily tape the tips (opposite the heads) of the cable ties in place to hold them.
- Install the 1-1/4" hose clamp around the tips of the cable ties, such that it is approximately 15" from the end of the pipe that is inserted in the bottle. Tighten the clamp firmly to secure.
- Glue the threaded male adapter onto the pipe on the end opposite the bottle.
- After the glue cures, wrap the male threads with 2-3 layers of Teflon tape, and screw it firmly into the threaded T fitting in the center of the launcher base. Use a gloved hand or channel lock pliers to secure the joint, but do not over-tighten. This joint can later be disassembled to make the launcher easier to transport.
- Blow out the candle, lest you burn down your abode.
Step 6: Add the Air Port
Add the air port to the base. You'll need:
- tire valve
- 4" to 6" piece of 1/2" PVC pipe
- 1/2" PVC end cap
- Drill a hole into the center of the 1/2" end cap with the 37/64" drill bit. It's an odd sized bit, so if you must, drill the hole smaller, and then enlarge it a bit with the tip of a knife or a rotary tool.
- Check the fit of the tire valve, by inserting it into the open end of the cap, pulling the stem through the hole. Pull the stem gently until the valve base seats correctly. Make any adjustments to the hole size, as needed.
- Remove the tire valve, apply glue to the inside of the hole in the cap, and reinsert the valve.
- Cut a piece of 1/2" pipe to a length of 4" to 6". Glue this pipe into the cap.
- Glue the air port assembly into the T connector (that has the solvent weld port) on the outer rim of the base. This extra pipe creates an air chamber in the launcher, which will help keep water away from the valve as it occasionally leaks into the base of the launcher.
Step 7: Assemble the Latch
This step adds the latch mechanism, which completes the launcher. You'll need these parts:
- 2 3D printed stopper clamp pieces (bottom right of photo)
- 1 3D printed cable tie retainer tube (left of photo)
- 1 3D printed firing chock (top of photo)
- #6 fasteners
- rubber bands or ponytail holders
- pull string
- Remove the bottle from the launcher.
- Using the #6 screws, attach the 2 stopper clamp pieces around the base of the cable ties, just above the hose clamp. The screws will thread into the holes of the stopper clamps, but you may wish to supplement this connection with the optional washers and nuts.
- Slip the cable tie retainer tube over the top of the launcher, and over the heads of the cable ties. The 4 square projections should be pointing upward.
- Reinstall the bottle on the top of the launcher. Make any necessary adjustment to the position of the cable ties such that they engage the rim of the bottle, while the bottle is wedged on the tapered section of the launcher tube.
- Slide the retainer tube upward so that it neatly collects the heads of the cable ties around the upper opening. The 4 square protrusions on the top of the retainer tube should gently touch the curved top of the bottle.
- Any time a new bottle is used, steps 4 and 5 must be repeated to re-calibrate the latching mechanism.
- Stretch the rubber bands or ponytail holders around the ears of the stopper clamp, and up to the ears on the retainer tube. Use one or more bands on each side, as needed, to ensure the retainer tube is reliably retracted away from the bottle.
- Thread one end of the pull string through the hole in the firing chock, and tie it firmly. Use several knots to ensure the line is firmly fixed.
- Insert the firing chock between the stopper clamps and the retaining tube so that the tube is held upward against the bottle. If necessary, adjust the position of the stopper clamps so that there is a total of about 1/16" play between the 3 pieces.
- Test the latching mechanism before pressurizing the system. Quickly tug the pull string so that the firing chock is completely removed from the launch tube. The retainer tube should then drop downwards (assisted by the rubber bands) and allow the cable ties to open freely.
Step 8: Wait
Allow the entire assembly to cure for a minimum of 24 hours before pressurizing. If you do not, joints are likely to blow apart, ruining your assembly, and possibly injuring someone.
Step 9: Check for Leaks
- Install the bottle and set up the latch mechanism by installing the firing chock as was done during the previous steps.
- Attach the bicycle pump to the tire valve and inflate to a pressure of 20 PSI. Remove the pump, and listen carefully for any air leaks. Watch the pressure gauge on the bicycle pump for 5-10 minutes to verify that there is no loss in pressure. Remember - your system is pressurized - treat it with the full respect of a loaded weapon, and do not leave it unattended.
- If any pipe joints leak, repair them immediately, and do not pressurize the system further until the repair is verified with another leak test.
- If air is leaking around the base of the bottle, gently depressurize the system, make the necessary adjustments to the latch mechanism, and then retest.
- Once a pressure test is completed successfully, gently depressurize the system and prepare for the launch...
Step 10: T Minus 9...8...
- Fill the soda bottle about 1/3 full with water.
- Lean the entire launcher to one side, so that you can insert the bottle over the launch tube, without spilling much of it.
- Set the latching mechanism and insert the firing chock so that the bottle is latched in place.
- Set the launcher upright, and be certain that the rocket is pointing directly skyward. Consider the direction of the wind, your immediate surroundings, and likely locations where the rocket could get stuck in a tree, break a window, or injure someone. Plan accordingly.
- Place the pull string in a location where it will not be accidentally triggered.
- Place 10 - 20 pounds of weight around the base of the launcher so that it does not tip over when the pull string is activated. Sandbags are the optimal choice, but large logs or large flat rocks will also work. Place these weights gently, so as not to damage the pipe around the base of the structure.
- Attach the bicycle pump, and begin pressurizing the system. Eye and face protection are strongly advised.
- It is recommended to begin with modest pressures of around 20 PSI until you are confident with the system, and you know what to do if and when a jam occurs.
- Gently stretch the string until all of the slack is removed.
- Begin your count down - the big moment is now here!
- Tug the string sharply to remove the firing chock, but not with excessive force. A quick snap of the wrist is all that is needed. Do not pull too slowly, or the launcher may begin to lean towards you. A misfire at this point could send a rocket directly at you.
- Have fun, and don't get cocky. 60 PSI is more than enough pressure to create an impressive launch. Work up to this pressure slowly to be sure your launcher is working well. Use extra caution as pressures increase, as the potential for a mishap increases dramatically.
- Seriously, DO NOT GO OVER 60 PSI, or you're risking life and limb. It's all fun and games until someone loses an eye. Or kidney.
Step 11: Rocket Level: Expert
Add a nose cone, parachute container, or stabilizer fins by helping me reach my stretch goals. Once more, that Kickstarter project is here: SHAMELESS PLUG
Good luck with your build!