3D Printing Compressed Air Tanks

Using PVC pipe as a pressure vessel for compressed air can be a fun and enjoyable hobby. It’s safe, too: while there are are reports of PVC pipe being the cause of accidents, these accidents include a black powder potato gun[1], and welding too close to a PVC pipe containing compressed air[2]. Compressed air stored in a PVC pipe is never a proximal cause in any accident, and the OSHA’s Fatality and Catastrophe Investigation Summaries bear this out; there was no industrial or occupational accident recorded in these summaries where a pressure vessel made out of PVC was the cause of any injury or death[3].

Although PVC pipe can be a perfectly safe, effective, and cheap pressure vessel for hobby applications, it’s not always the best choice. A group of students in Renens, Switzerland are building autonomous robots for the Eurobot competition, and this year’s robot uses pneumatics. That means compressed air, and that means a pressure vessel. Since just about everything else on this robot is 3D printed, they asked the obvious question. Is it possible to 3D print a tank for compressed air?

The tank for this robot would only be used up to about 4 bar (400kPa), and after a few quick calculations, the team discovered the wall thickness – even in a pressure vessel with corners – would be pretty low. The first prototype, a 40mm cube with 20% infill and a hole drilled in the side, held 6.5 bar (650kPa) for an hour. This success didn’t last, though: he second prototype, a 65x40x80mm rectangular prism printed without as much infill, exploded at 5.5bar (550kPa).

The third time’s the charm, and with filleted ribs inside the tank, the third prototype was able to hold pressure up to 6.5 bar. Of course no 3D print is perfect, and the third prototype did leak, but a bit of acrylic spray paint applied to the outer surfaces held the air in.

While it’s not as fun, easy, cheap, rewarding, or safe as using PVC pipe as a pressure vessel, the team did manage to build a 3D printed pressure vessel with a custom shape. You can’t do that very easily with round pipe. And 3D printing opens up all manner of internal structure to experiment with. We’d like to see this developed even further!

Sources: [1], [2], [3]

Feeding The Cat, Reinventing the Wheel

There are few projects that we see as many iterations of as the pet feeder or the plant waterer. (What is it with you people? Are you all as forgetful as we are?) Still, the fun is in the details of the implementation. Or at least that’s the case with [Emmaanuel]’s cat feeder.

The writeup is split into three parts: the worm-drive, the electronics, and the housing (here in English: worm, electronics, housing). And of course, there’s a video inlined below.

The auger and motor housing make great use of PVC pipe and 3D printing, and the dispenser unit looks quite professional. There’s not all that much to say about the electronics — an Arduino clone, an LCD, and a cheap gear motor do just about what you’d expect.

The CNC’ed case with spring-fit tabs steals the show, however. It’s made out of MDF, which doesn’t take well to screwing or glueing. With carefully routed pins and tabs that have a little spring in them, [Emmaanuel] was able to take the pieces off the mill table and just snap them together. Awesome.

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Feed the Fun with a Semi-automatic Cheesy Poof Rifle

At Hackaday we think that hackers have the power to make the world a better place with their builds. This air-powered cheesy-poof rifle is not one of those builds, unless making the world a little more fun and slightly messier makes it a better place.

The principle of [NightHawkInLight]’s design is simple – an electric leaf blower provides the power, and a big vat o’ poofs provides the ammo. Getting the two together and providing a barrel is a matter of some simple plumbing with 1″ PVC pipe and fittings. But wait – lest you think this hack, like the ammo, is just a delicious bit of fluff, there’s something to be learned about fluid dynamics here. With a plain tee fitting, the leaf blower would only pressurize the magazine, making it difficult to chamber a round. But by adding a small restriction to the incoming air flow, the Venturi effect actually sucks ammo into the chamber and down the barrel, to the delight of hungry wildlife for yards around. Science!

There’s plenty of room for improvement to the design – something along the lines of this gas-powered, tube-fed snowball gun would be keen. As it stands, the cheesy-poof gun seems like good, unclean fun.

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A Structural PVC Cyr Wheel

PVC is a great building material that can be used for everything from yurts and geodesic domes to pressure vessels. One thing we haven’t seen a lot of is bending PVC pipe. [Lou] wanted to build a Cyr wheel for his daughter, and instead of shelling out five hundred big ones for an aluminum version, he build one out of PVC using techniques usually reserved for woodworking.

A Cyr Wheel is usually a large aluminum hoop built for acrobatic performances. These performances are pretty impressive and look like a lot of fun, but the wheels themselves are rather expensive. Figuring PVC was a good enough solution, [Lou] built his own Cyr wheel for $50 in materials.

The build started off by laying out a jig on the floor. Two sheets of plywood were laid out, a radius for the wheel traced, and a bunch of blocks were glued to the perimeter of this mold. With the mold in place, a few pieces of PVC were flexed into position, clamped, heated with a hair dryer to relieve stress, and glued to a second course of PVC.

The process [Lou] used to build his Cyr wheel isn’t that different from extremely common woodworking techniques. In fact, it wouldn’t be unreasonable for [Lou] to build a wooden Cyr wheel with the same jig. We’re wondering how well this project will stand up to abuse, so if you have any insight to the uses of structural PVC drop a note in the comments.

Air Rocket Launch Pad UI Entertains Eager Kids

Last spring [Mike] built a foam rocket launchpad which was a hit with the kids in his neighborhood. But the launch system was merely a couple of buttons so the early enthusiasm quickly wore off. He went back to the drawing board to make improvements and really hit the jackpot!

The original launch system had one button for building up air pressure with a second big red button of doom for launching the rocket. The problem was a complete lack of user feedback; all the kids could do is guess how long they needed to hold the button to achieve the highest launch. This revision adds flashing LEDs to hold the attention of the wee ones but to also function as a gauge for the new pressure control system. The visually fascinating control board also includes a removable key to prevent accidental launches.

The particulars of this are as you’d expect: it’s a bunch of plumbing to manage the air pressure, an Arduino to control it all, and additional electronics in between to make them work together.

We’re especially impressed by the leap in features and quality from the first version to this one. It’s a testament to the power of quick proofs-of-concept before committing to a more involved build. Great work [Mike]!

We’ve seen rocket launchers for adults and some neat mission control panels but [Mike’s] kid friendly launch controller really is out of this world (sorry, couldn’t resist). You’ll find a video demo of this launcher after the break.

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How to Rescue Your Quadcopter from a Tree

Whether it’s a new rocket, your latest quadcopter, or [Charlie Brown]’s kite, it always seems like there’s a tree waiting to catch and eat airborne projects. Sometimes you get lucky and find a way to climb up the tree to retrieve your wayward build, but most times you’re reduced to looking for rocks or sticks to fling up there in an attempt to shake it loose. But if you want to improve your chances of getting your stuff back, [U.S. Water Rockets] has a build for a retrieval tool made mostly from scrap bin parts that will help.

All you need is some PVC tubing, an old fishing reel and line, some latex surgical tubing, and a few dowels for projectiles. You can tell everything about the build from the BOM and stills, but the video after the break gives detailed instructions and shows it in action. Adding some fins to the dart or even substituting a cheap arrow from the sporting goods department of your favorite retailer might help with your aim. Even without fletching, the accuracy of the launcher is pretty good, and the range isn’t half bad either. Once the fishing line is over the branch that ate your quad it can be used to haul up successively stouter ropes, and pretty soon you’ll be shaking the tree like a boss.

Even if getting stuff out of trees isn’t on your immediate to-do list, this little hack could be put to other uses. Hams will use it to loft antennas up into trees, and tag-line placement for tree removal could be simplified with this tool. But if you still find yourself needing to retrieve stuff, you might want to be proactive and make your aerial robot tree-proof. That still won’t eliminate the need for drone-on-drone rooftop rescues.

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Thar be Beer in These Walls

When you need a cold one and walking downstairs to your twin-keg refrigerator just won’t do, it’s time to break out the tools to deliver that frothy goodness where it’s needed. And so began [DaveLondres’] inspiring tale of piping beer through the walls of his home.

Now we know what you’re thinking… that beer is going to get mighty warm sitting in long lines from the fridge up to the ground floor. [Dave] thought about that too and designed a double-pipe system to overcome the issue. A run of PVC pipe for each keg connect the in-wall taps to holes drilled in the side of a second-hand fridge. An ingenious branching job yields an extra port for each run which was fitted with computer case fans to keep the cold air circulating. Plastic tubing is snaked inside of the PVC to carry the beer.

Rounding out the craftsmanship on this one is the inclusion of a plumbed drain to whisk away the drippings. If you’re not going to have a beautifully adorned chest-freezer-gone-kegerator in your livingroom this is the best alternative we’ve seen.

[via reddit]