We were using the same 9v batteries for many days. We took them to quite a few airshows where they were used all day (over 7 days) and I haven't had to change the batteries in any of them. I did notice that you are using an Orbit sprinkler valve, and I have only used the Rainbird valves. That's all that I can think of for the difference in run times. Might be worth trying a Rainbird valve if you build another? (I can't imagine they would be that different though). I modified the input side to connect a pop-off and the valve stem. Doing it this way allows the rest of the design to stay the same, but it does make the design more expensive and larger. Glue one of the elbows to the Tee and while pushing the pieces firmly together, and make the launch tube parallel with the 13 inch tube. Since the launch tube essentially multiplies the angle at the T and elbow joint, you should be able to get them lined up closely. Drill a hole in a the 1.25 inch PVC cap for the button. The size needed will be different for whichever button you use.

Very similar indeed! If you'll notice in my pictures I had a _small_ accident with the primer (and lost many of the numbers on my square). My would kill me if I brought that stuff anywhere near the dining room table, protective covering or not! ;D Screw the launch tube into the 3/4 inch Tee before gluing the T assembly to an elbow. Use this to make sure the Tee is lined up with the 13 inch tube correctly.If you're using a 3/4 inch sprinkler valve, then use a 1 inch threaded PVC plug. If you are opting for a bigger 1 inch sprinkler valve, then use a 3/4 inch threaded PVC plug. Start by finding the center of the PVC plug and drill a hole with the smaller drill bit. The size doesn't matter, it is just to keep the bigger drill bit from walking. But that's for new well care for pipe, not something that is getting bumped around constantly, pressurized and depressurized, and worst of all - left out in the sun to deteriorate the PVC. Sadly, as with all things, the integrity of your launcher will eventually deteriorate until it fails. So we take steps to lengthen the time to failure and reduce the hazard when that failure occurs. Do NOT use the launcher in the cold. PVC becomes brittle when it gets cold, and it does not fail in a graceful way. Fantastic instructable! Thanks for taking the time to put all this together. I really appreciate all the shared learnings from your experiments. I can't wait to put this together for all our nieces and nephews at the family reunion. I usually refrain from interfering with students' designs, however if a student has created a poorly built fuselage I will step in and help them. Making a new fuselage after attaching everything else can be a hassle.

Yes, that's a great idea! I looked at them, and the price was the main reason I didn't include them in this build. All of the bike pumps we've been using have gauges built in, so we have the students use them (also the younger groups we always have an adult helping them). The sprinkler valve is the weak link for this size pipe, and it is rated for 150 PSI I think. Never allow students to use the launcher unsupervised. Disable the launcher by removing the battery (or pump or launch tube) if you have to leave the launcher unsupervised. The valve brace relieves any stress that might happen to the sprinkler valve connections, and will help make the launcher last longer.

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I made a very detailed video on how to build a launcher, but since it is such a long video, I made this tutorial as well since seeing the steps one at a time is sometimes easier. If you have any questions, more than likely they are in this video. Or if you just prefer video instructions, take a look here: I'd love to see more on how you built your buttons. I'm looking at finding a cheap NO momentary button wired to a few 9v bats in a 3d printed case. Take the solenoid off of the sprinkler valve (just unscrews by hand, see the photos). If you don't do this, the solenoid will hit the frame body and won't screw onto the frame. AFTER a few hours, the glue should be fully set. It only takes a couple minutes for the glue to hold, but it doesn't hurt to be cautious. I usually wait a full day just in case. A final update here: we had two launch events and the new launchers were wonderful! they upped the fun factor by like 3-4x! Thanks so much for your work here!

Don't forget to sand about an inch on one side of the launch tube, and then sand the inside of the 3/4 inch to 1/2 inch connector. Hold the pieces together firmly for 10 seconds while the glue sets. If you don't hold the pieces pushed together, they will push apart! Have a countdown before each launch as a way to alert people in the area (and to make each launch more exciting!) Connect the speaker wires to the sprinkler valve. The positive and negative do not matter for the valve. After gluing the second elbow to the Tee, I pushed the "mouths" of the elbows flat onto the table to try to get them as parallel as possible. If they aren't parallel, it will be very hard to fit this Tee assembly onto the rest of the launch tube.

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For the valve stem plug, you say to use a 1in threaded plug I f there is a 3/4in sprinkler valve; or use a 3/4in threaded plug if you use a 1in sprinkler valve. Why is this? I realize you went all 1in outlets in latter designs. I will continue with this build for now, anticipating that it will be for lower-pressure launches for fun and teaching, and not high-pressure launches to impress the neighbours. Glue one elbow to the Tee making sure that the threaded Tee opening is facing the same direction as the elbow opening.

As for the residual charge, any kind of load should eat the voltage (such as a light bulb, but just make sure a resistor is used to drop the voltage so that the bulb won't be blown out).If using an electric miter saw, we found it best to put the PVC in place, start the saw off of the PVC, bring the saw down through the pipe, and then leave the saw down until the blade has stopped. Otherwise the blade could chip the pipe. This is an optional step, but adding it prevents users from over-pressurizing the system to a point of failure. Thanks to aaron.linker for suggesting it! If the pressure goes over the max set on the relief valve, it will "pop" to relieve the pressure and then close again.