A Tutorial On Using Linux For Real-Time Tasks

April 25, 2014 by 15 Comments

[Andreas] has created this tutorial on real-time (RT) tasks in Linux. At first blush that sounds like a rather dry topic, but [Andreas] makes things interesting by giving us some real-world demos using a Raspberry Pi and a stepper motor. Driving a stepper motor requires relatively accurate timing. Attempting to use a desktop operating system for a task like this is generally ill-advised. Accurate timing is best left to a separate microcontroller. This is why we often see the Raspi paired with an Arduino here on Hackaday. The rationale behind this is not often explained.

[Andreas] connects a common low-cost 28BYJ-48 geared stepper motor with a ULN2003 driver board to a Raspberry Pi’s GPIO pins. These motors originally saw use moving the louvers of air conditioners. In general, they get the job done, but aren’t exactly high quality. [Andreas] uses a simple program to pulse the pins in the correct order to spin the motor. Using an oscilloscope, a split screen display, and a camera on the stepper motor, [Andreas] walks us through several common timing hazards, and how to avoid them.

The most telling hazard is shown last. While running his stepper program, [Andreas] runs a second program which allocates lots of memory. Eventually, Linux swaps out the stepper program’s memory, causing the stepper motor to stop spinning for a couple of seconds. All is not lost though, as the swapping can be prevented with an mlockall() call.

The take away from this is that Linux is not a hard real-time operating system. With a few tricks and extensions, it can do some soft real-time tasks. The best solution is to either use an operating system designed for real-time operation, or offload real-time operations to a separate controller.

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3D Printed Hydrofoil Boat RC Flies

April 25, 2014 by 20 Comments

hydrofoil boat

[Wersy] has been trying out different designs for 3D printed RC boats — his latest is a hydrofoil!

He’s using a high power RC plane out-runner motor, which he found is simply… too powerful. It would cause his first boat to flip and sink if he opened the throttle up too much! To counter this — and make full use of his motor — he’s made new two boats; a hydrofoil, and a dual-hulled  air(?) boat.

He based the hydrofoil’s profile off of NACA 63-412, a typical profile for sailboat hydro foils like the Moth. What he found was it’s still extremely difficult to get the right balance between the pitch of the wings, and the throttle output to hit a steady condition for driving smoothly. It works, but it will still needs a few more iterations!

His other solution, a quasi-jet engine-dual-hulled-boat is pretty fun too — he’s 3D printed a large impeller for his motor, and strapped it in between two of his boats! It’s quite a bit more stable to drive, and looks pretty unique!

Stick around after the break to see both of them in action.

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Sci-Fi Contest Roundup: I Am Iron Man

April 25, 2014 by 5 Comments

Back when Iron Man 2 and The Avengers were out in theaters, the Hackaday tip line couldn’t go a week without an arc reactor build being submitted. In keeping with the Internet’s fascination with blinkey glowey things, we expected a huge influx of arc reactors for our Sci-Fi contest. We were pleasantly surprised: all the submissions from the Marvel universe are top-notch, and the two Iron Man entries we have are simply amazing.

Motorized Helmet

1[James Bruton] is working on a replica of the Iron Man movie helmet, complete with a motorized face plate, light up eyes, and an OLED display for a reasonable facsimile of the horribly unrealistic on-screen heads-up display.

While a few bits and bobs of the mechanics were 3D printed, [James] is making the majority of the helmet just as how the on-screen version was made. The helmet was first carved out of sheet foam, then molded and cast into very strong rigid fiberglass. [James] put up a great tutorial series on how he did this and other parts of his Iron Man costume.

Anamatronic

2The other Iron Man costume from [jeromekelty] and [Greg Hatter] doesn’t stop at just the helmet. They’re doing everything: shoulder-mounted rocket pods, hip pods, forearm missiles, back flaps, and boots with a satisfying electronic kerthunk sounding with every step.

Inside the custom molded suit are at least four Arduinos, four XBees, an Adafruit WaveShield, and at least 20 servos for all of the Iron Man suit components. The mechanics are actuated via RFID with a tag in a glove; when the wearer waves their hand over some part of the suit, one of the mechanical features are activated.

It’s impressive to say the least, and one of the best documented projects we’ve seen in the Sci-Fi contest.

There’s still time to put together your own Sci-Fi project for the contest. Grab your soldering iron and fiberglass resin, because there’s some seriously great prizes up for grabs.

 

A High-Speed Logic Gate Board For The Easy-Phi Project

April 24, 2014 by 16 Comments

A (long) while ago I presented you the Easy-phi project, which aims at building a simple, cheap but intelligent rack-based open hardware/software platform for hobbyists. With this project, you simply have a rack to which you add cards (like the one shown above) that perform the functions you want.

During these last months my team has been finishing the design and production of several different boards so I’ll start showing them off during these next weeks. Today I present you the High Speed Logic Gate Board, a quantum-physicist requested easy-phi module that can perform logic AND/OR functions at <2GHz speeds. This quite technical write-up is mainly about the constraints that high-speed signals pose for schematics design but is also about the techniques that are used for HS signals termination and monitoring. I hope, however, it’ll give our readers a nice overview of what the insides of a high-speed system may look like. All the files used for this board may be found on the official GitHub repository.

HexDrake — A Low Cost 2-DOF Hexapod

April 24, 2014 by 6 Comments

hexdrake low cost hexapod

[David’s] been making robots since he was 16. After conquering the basics, he wanted to build something a bit more interesting than a simple wheeled-robot — he wanted to buy a hexapod but they were too expensive — so he decided to design his own low-cost version!

It’s made out of hand-cut wood, SG90 servos, an Arduino and a 16-channel servo controller. A 2.4GHz remote control sends commands to the Arduino which then communicates to the USC servo controller, allowing for intricate control of the 14 servos that make up the HexDrake.

He’s also added a few LED arrays for the eyes of his robot, which in the future will be animated to give expression to his little hexapod.

It’s an extremely well built little bot, and [David’s] made a very in-depth Instructable for anyone who would like to follow in his footsteps. Stick around after the break to see it scurry around!

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Building EL Displays On A PCB

April 24, 2014 by 26 Comments

ELElecrolumiscent displays have seen a huge swing in popularity recently, but only in limited forms like EL wire or flat EL panels. You can, of course, cut and bend these wires and panels to suit any purpose, but custom shaped EL displays are just the bee’s knees. They’re not hard to fabricate, either: with cheap custom PCBs, all it takes to make custom EL panels is just a few chemicals.

[Nick]’s method of fabricating custom EL displays uses an exposed copper layer on a PCB you’d pick up from OSHpark or any of the random board houses in China. The process consists of designing a display – be it a few letters, pixels, or a seven-segment arrangement. The display ‘stack’ is a layer of painted-on dialectric, a phospor, and finally a translucent conductive ink that connects the display segments to ground. It looks like an extremely easy process, and from the pictures it looks like [Nick] is making some EL displays of reasonable quality.

[Nick]’s work was inspired by the grand poobah of homebrew electrolumiscent displays, [Jeri Ellsworth], who managed to make a similar EL pixel on a PCB. [Nick]’s display looks great, though, and with a little work some custom segment displays should be very possible.

Morphex Ready To Roll

Sphere Morphing Hexabot Takes On The Wilderness

April 24, 2014 by 16 Comments

[Zenta’s] sphere morphing hexabot, the MorpHex, continues to impress us. He’s just released a video showing it off — by having it roll down a hill!

We’ve been following the MorpHex since 2011, and it really is an amazing project — especially when it started to roll around on its own! In this latest update, [Zenta] was trying to get a good outdoor test video, as he’s never seen a hexapod robot roll down a hill. The video (and rolling) goes smoothly until about 3 minutes 36 seconds in, when the MorpHex experiences a catastrophic inner body servo failure!

Surprisingly, it didn’t fail during its tumble down the hill, but when it was just walking around afterwards. [Zenta] attributes it to a poor quality servo and had bad feelings about it breaking previously. Not fixing it earlier resulted in having to spend 10 hours of his Easter holiday taking Morphex apart and repairing it! Just goes to show… don’t wait until it’s too late to fix something!

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