Raspberry Pi Opens Doors

The Raspberry Pi is a cheap credit card sized computer that has opened the doors of embedded Linux to millions of people. But in this case, it’s literally opening a door. The Computer Club at Western Michigan University had to move to a different room which brought with it a new challenge. The door handle was more difficult to turn than the old one. Nothing that a NEMA 17 stepper couldn’t handle, however.

After printing a few gears and wiring up an Easy Driver board between the Raspi and stepper motor, they had the basics of a door opener in place. A 5v relay is used to keep the power off the stepper when not in use, and a limit switch is used to monitor the position of the door handle while a Hall Effect sensor tells when the door is open and shut.

Be sure to check out the project as all source, parts list and schematics are available in case you have a simliar door that needs amending.

Full Size Custom Claw Machine Built with Parts on Hand

You know how it goes – sometimes you look at your social calendar and realize that you need to throw together a quick claw machine. Such was the dilemma that [Bob Johnson] found himself in during the run-up to the Nashville Mini Maker Faire, and he came up with a nice design that looks like fun for the faire-goers.

Seeking to both entertain and enlighten the crowd while providing them with sweet, sweet candy, [Bob] was able to quickly knock together a claw machine using mainly parts he had on hand in the shop. The cabinet is nicely designed for game play and to show off the gantry mechanism, which uses aluminum angle profiles and skate bearings as custom linear slides. Plenty of 3D printed parts found their way into the build, from pillow blocks and brackets for the stepper motors to the servo-driven claw mechanism. A nice control panel and some color-coded LED lighting adds some zip to the look, and a Teensy LC runs the whole thing.

Like [Bob]’s game, claw machines that make it to Hackaday seem to be special occasion builds, like this claw machine built for a kid’s birthday party. Occasion or not, though, we think that fun builds like these bring the party with them.

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Simple, Cheap Nitrate Tester is Open Source

Too much of a good thing can be a bad thing, and nitrate pollution due to agricultural fertilizer runoff is a major problem for both lakes and coastal waters. Assessing nitrate levels commercially is an expensive process that uses proprietary instruments and toxic reagents such as cadmium. But [Joshua Pearce] has recently developed an open-source photometer for nitrate field measurement that uses an enzyme from spinach and costs a mere $65USD to build.

The device itself is incredibly simple – a 3D printed enclosure houses an LED light source and a light sensor. The sample to be tested is mixed with a commercially available reagent kit based on the enzyme nitrate reductase, resulting in a characteristic color change proportional to the amount of nitrate present. The instrument reads the amount of light absorbed by the sample, and communicates the results to an Android device over a Bluetooth link.

Open-source instruments like this can really open up educational opportunities for STEM groups to get out into the real world and start making measurements that can make a difference. Not only can this enable citizen scientists and activists, but it also opens the door for getting farmers involved in controlling nitrate pollution at its source – knowing when a field has been fertilized enough can save a farmer unnecessary expense and reduce nitrate runoff.

There are a lot of other ways to put an open-source instrument like this to use in biohacking – photometery is a very common measuring modality in the life sciences, after all. We’ve seen similar instruments before, like a DIY spectrophotometer, or this 2015 Hackaday Prize entry medical tricorder with a built-in spectrophotometer. Still, for simplicity of build and potential impact, it’s hard to beat this instrument.

Open Source, 3D Printed Rocket Engines

A liquid-fuel rocket engine is just about the hardest thing anyone could ever build. There are considerations for thermodynamics, machining, electronics, material science, and software just to have something that won’t blow up on the test rig. The data to build a liquid engine isn’t easy to find, either: a lot of helpful info is classified or locked up in one of [Elon]’s file cabinets.

[Graham] over at Fubar Labs in New Jersey is working to change this. He’s developing an open source, 3D printed, liquid fuel rocket engine. Right now, it’s not going to fly, but that’s not the point: the first step towards developing a successful rocket is to develop a successful engine, and [Graham] is hard at work making this a reality.

This engine, powered by gaseous oxygen and ethanol, is designed for 3D printing. It’s actually a great use of the technology; SpaceX and NASA have produced 3D printed engine parts using DMLS printers, but [Graham] is using the much cheaper (and available at Shapeways) metal SLS printers to produce his engine. Rocket engines are extremely hard to manufacture with traditional methods, making 3D printing the perfect process for building a rocket engine.

So far, [Graham] has printed the engine, injector, and igniter, all for the purpose of shoving oxygen and ethanol into the combustion chamber, lighting it, and marveling at the Mach cones. You can see a video of that below, but there’s also a few incredible resources on GitHub, the Fubar Labs wiki, and a bunch of pictures and test results here.

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3D Printed Surfboard

You whippersnappers these days with your 3D printers! Back in our day, we had to labor over a blank for hours, getting all sweaty and covered in foam dust. And it still wouldn’t come out symmetric. Shaping a surfboard used to be an art, and now you’re just downloading software and slinging STLs.

Joking aside, [Jody] made an incredible surfboard (yes, actual human-sized surfboard) out of just over 1 kilometer of ABS filament, clocking 164 hours of printing time along the way. That’s a serious stress test, and of course, his 3D printer broke down along the way. Then all the segments had to be glued together.

But the printing was the easy part; there’s also fiberglassing and sanding. And even though he made multiple mock-ups, nothing ever goes the same on opening night as it did in the dress rehearsal. But [Jody] persevered and wrote up his trials and tribulations, and you should give it a look if you’re thinking of doing anything large or in combination with fiberglass.

Even the fins are 3D printed and the results look amazing! We can’t wait for the ride report.

Shaka.

A Cute Little 3D Printed Skateboard

[Julian] has been wanting a tiny little skateboard for a while now, and decided to make something useful on his 3D printer. A little more than twenty hours later a tiny and cute printed skateboard popped out.

[Julian] got the files for his 3D printed skateboard from Thingiverse and printed them off on a MakerGear M2. The parts printed easily, each part taking about six hours to print. The parts are bolted together with five threaded rods, the trucks were screwed on, and the wheels popped into place.

While a normal skateboard probably wouldn’t stand up to the 3D printed parts and threaded rod construction, this Pennyboard is tiny, and most of [Julian]’s weight is right over the trucks at all times. This is also not a board that’s going to see a lot of tricks; it’s basically a micro longboard for moving from one place to another, not something you’ll need to find an abandoned in-ground pool to use properly.

You can check out the video below.

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