Hackaday Prize Semifinalist: An Affordable Robotic Arm

Industrial robot arms are curious devices, found everywhere from the back of old engineering classrooms where they taught kinematics in the 90s, to the factory floor where they do the same thing over and over again while contemplating their existence. For his Hackaday Prize entry, [Dan] is building a big robot arm. It’s not big enough to ride on, but it is large enough to automate a few processes in a reasonably well-equipped lab.

This is not a tiny robotic arm powered by 9 gram hobby servos. For the bicep and tricep of [Dan]’s arm, he’s using linear actuators – they’re high precision and powerful. A few months ago, [Dan] tried to design a hypocycloid gear but couldn’t get a $3000 prototype to work. Although the hypocycloid is out, he did manage to build a strange differential pan/roll mechanism for the wrist of the arm. It really is a thing of beauty, and with the engineering [Dan] has put into it, it’s a very useful tool.

If you’d like to meet [Dan]’s robot arm in person, he’ll be at the 2015 NYC Maker Faire this weekend. Check out [Dan]’s Hackaday Prize video for his robot arm below.

The 2015 Hackaday Prize is sponsored by:

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Fully-Automatic CD Launcher Looks Dangerously Fun

When [JZSlenker] was challenged to find a creative way to destroy a bunch of compact discs that were burned incorrectly, he did not disappoint. He came up with a rather simple but fun contraption that launches the CD’s at high speeds and with a fast rate of fire. He doesn’t share many details about how this machine was built, but the 18 second video makes it pretty obvious how it works.

The CD gun is built mainly from a piece of plywood. This provides a flat base with which to mount the other components. A stack of compact discs is held in place by what appears to be a metal cage that was welded together. An inexpensive angle grinder is used as the propulsion mechanism. The grinding wheel is mounted just in front of the stack of CD’s in a vertical orientation. The wheel must be placed just high enough above the plywood base for a CD to fit in between the wheel and the base. This design is remarkably similar to the Sticker Gun which our own [Brian Benchoff] is building.

Some type of linear actuator is used as the firing mechanism. The actuator is hooked up to a thin piece of metal, cut into an L shape. It almost looks like a reaper tool. When a button is pressed, the actuator fires instantly. This pushes the metal hammer into the CD on the bottom of the stack. The CD is pressed forward into the grinder wheel which then shoots the CD into the air. Based on the below video, it looks like [JZSlenker] is able to fire at a rate of about three CD’s per second with this rig.

This has got to be a super-villain weapon for an upcoming movie, right? Maybe AOL-man?

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Secret Attic Library Door

We have a pretty good guess where [Krizbleen] hides away any seasonal presents for his family: behind his shiny new secret library door. An experienced woodworker, [Krizbleen] was in the process of finishing the attic in his home when he decided to take advantage of the chimney’s otherwise annoying placement in front of his soon-to-be office. He built a false wall in front of the central chimney obstacle and placed a TV in the middle of the wall (directly in front of the chimney) flanked on either side by a bookcase.

If you touch the secret book or knock out the secret sequence, however, the right-side bookcase slides gently out of the way to reveal [Krizbleen’s] home office. Behind the scenes, a heavy duty linear actuator pushes or pulls the door as necessary, onto which [Krizbleen] expertly mounted the bookcase with some 2″ caster wheels. The actuator expects +24V or -24V to send it moving in one of its two directions, so the Arduino Uno needed a couple of relays to handle the voltage difference.

The effort spent here was immense, but the result is seamless. After borrowing a knock-detection script and hooking up a secondary access button concealed in a book, [Krizbleen] had the secret door he’d always wanted: albeit maybe a bit slow to open and close. You can see a video of its operation below.

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DIY Linear Actuators For A Flight Sim


[Roland] has already built a few very cool and extremely realistic flight sims, but his latest project will put his current rig to shame. He’s building a six degree of freedom simulator based on homebuilt linear actuators of his own design.

The actuator is powered by a large DC motor moving timing belts along the length of the enclosure. These timing belts are connected to a shaft that’s coupled to the frame with a few bungee cords. The bungee cords are important; without them, the timing belts would be carrying all the load of the sim – not a good thing if these actuators are moving an entire cockpit around a living room.

Also on [Roland]’s list of awesome stuff he’s building for his flight sims is a vibration system based on the BFF Shaker. This board takes data in from sim software and turns it into vibrations produced by either unbalanced DC motors or one of those ‘bass kicker’ transducers.

It’s all very cool stuff, and with all the crazy upgrades [Roland] is doing to his sim rig, he’s doing much better than paying $300/hour to rent a Beechcraft Baron.

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Fail of the Week: Physical Pixel Display


This physical pixel display reminds us of a couple of different hacks that we’ve seen over the years. It looks impressive, but [Matt] couldn’t quite get it to work. It wasn’t the Kinect sensor and image interpretation that was the problem. It was a failure to get the hardware components seen above to perform reliably.

If you can’t figure out what this is supposed to do, take at look at the inFORM morphing table or the pixel wall installed at the Hyundai expo last year. [Matt’s] attempt is much more modest with a grid of just 10×6. The pixels themselves are ballpoint pens (he gets bonus points for cheap and easy materials). The pens move in and out thanks to some Bowden cables connected to hobby servos. The mechanical engineers have probably already figured out the fail… the pixels seem to get hung up and despite several revisions in the materials used , it couldn’t be fixed.

The hobby servos were chosen because they are much less expensive than proper linear actuators. We thought maybe [Matt] should build his own solenoids but that’s not a great idea because you can’t have variable depth that way (can you?).  Perhaps the pens should be vertical and the servos could pull on a string attached to the pen via a pulley with gravity to return them to the starting position? There’s got to be an inexpensive and relatively simple way get this thing working. Let us know how you’d get the project back on track by leaving a comment below.

2013-09-05-Hackaday-Fail-tips-tileFail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.

Super Angry Birds is a physical controller for the game

This role reversal is quite entertaining. While the game Angry Birds is a virtual realization of knocking over stuff with a sling-shot, Super Angry Birds adds a physical control element back to the virtual game. It’s silly, but well-executed. The main controller takes advantage a part which we don’t see used very often. It’s a motorized linear actuator which would most often be seen on a high-end audio console.

Check out the video after the break to see the controller in action. The linear encoder is used to simulate pulling the rubber sling shot back. It uses the motorized feature to spring back in place, but we’re not sure whether or not the motor also provides resistance during the pull. The laser cut case also includes a companion in the form of a TNT trigger box al-a Wile E Coyote.

If this isn’t real enough for you perhaps this slingshot controller will suffice.

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An easy to build cat feeder driven by a DIY linear actuator


[Will Finucane] of Revolt Labs/Mad Science Blog was looking for a way to keep his cats happily fed while away on a short vacation, so he put together a cheap and easy automatic feeder to ensure that his pets didn’t go hungry while he was away.

We’ve seen different iterations of automatic pet feeders here before, some relying on rotating false bottoms, while others use crank-style feeders to get the job done. [Will’s] solution is a bit different, employing a cheap linear actuator to deliver feedings.

He emptied out a glue stick, replacing the glue with a brass tube. This gives him the rigidity that the glue lacked, allowing him to easily move a platform full of cat food up and down. He mounted the glue stick on a continuous rotation servo, installing the actuator and a feeding platform inside a cardboard box.

Using an Arduino, he lowers the movable platform every 12 hours, allowing a bit of cat food to fall from the hole he cut in the side of the box. While his creation might not stand up to years of use, it’s a quick solution that can cost very little, depending on what you have sitting around.

Check out the video below to see [Will’s] cat feeder in action.

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