DIY Magnetic Actuator, Illustrated And Demonstrated

Electromagnetic actuators exert small amounts of force, but are simple and definitely have their niche. [SeanHodgins] took a design that’s common in flip-dot displays as well as the lightweight RC aircraft world and decided to make his own version. He does a good job of explaining and demonstrating the basic principles behind how one of these actuators works, although the “robotic” application claimed is less clear.

It’s a small, 3D printed lever with an embedded magnet that flips one way or another depending on the direction of current flowing through a nearby coil. Actuators of this design are capable of fast response and have no moving parts beyond the lever itself, meaning that they can be made very small. He has details on an imgur gallery as well as a video, embedded below.

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A Stepper Motor for Two Dimensions

We’ve all heard linear motors, like those propelling Maglev trains, described as “unrolled” versions of regular electric motors. The analogy is apt and helps to understand how a linear motor works, but it begs the question: what if we could unroll the stator in two dimensions instead of just one?

That’s the idea behind [BetaChecker’s] two-axis stepper motor, which looks like it has a lot of potential for some interesting applications. Build details are sparse, but from what we can gather from the videos and the Hackaday.io post, [BetaChecker] has created a platen of 288 hand-wound copper coils, each of which can be selectively controlled through a large number of L293 H-bridge chips and an Arduino Mega. A variety of sleds, each with neodymium magnets in the base, can be applied to the platen, and depending on how the coils are energized, the sled can move in either dimension. For vertical applications, it looks like some coils are used to hold the sled to the platen while others are used to propel it. There are RGB LEDs inside the bore of each coil, although their function beyond zazzle is unclear.

We’d love more details to gauge where this is going, but with better resolution, something like this could make a great 3D-printer bed. If one-dimensional movement is enough for you, though, check out this linear stepper motor that works on a similar principle.

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Hackaday Prize Entry: Adaptive Guitar

Due to a skiing accident, [Joe]’s new friend severed the motor nerves controlling her left arm. Sadly she was an avid musician who loved to play guitar — and of course, a guitar requires two hands. Or does it? Pressing the string to play the complex chords is more easily done using fingers, but strumming the strings could be done electromechanically under the control of a foot pedal. At least that’s the solution [Joe] implemented so beautifully when his friend’s family reached out for help.

There are just so many things to enjoy while reading through [Joe]’s project logs on his hackaday.io page, which he’s entered into the Hackaday Prize. He starts out with researching how others have solved this problem. Then he takes us through his first attempts and experiments. For example, an early discovery is how pressing the strings on the fretboard pulls the string down where the picks are located, causing him to rethink his initial pick design. His criteria for the pick actuators leads him to make his own. And the actuators he made are a thing of beauty: quiet, compact, and the actuator body even doubles as part of a heat sink for his custom controller board. During his pick design iterations he gets great results using spring steel for flexibility leading up to the pick, but thinking of someday going into production, he comes up with his own custom-designed, laser-cut leaf springs, different for each string.  Needing Force Sensitive Resistors (FCRs) for the foot pedal, he iterates to making his own, laying out the needed interlinked traces on a PCB (using an Eagle script) and putting a piece of conductive rubber over it all. And that’s just a sample of the adventure he takes us on.

In terms of practicality, he’s made great efforts to make it compact and easy to set up. The foot pedal even talks to the control board on the guitar wirelessly. Non-damaging adhesives attach magnets and velcro to the guitar so that the control board and pick bridge can be precisely, yet easily, attached single-handedly. The result is something easy to manage by someone with only one working hand, both for set-up and actual playing. See it for yourself in the video below.

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Super Simple Hydraulics Using Syringes

When making a toy excavator arm, or any robotic arm, the typical approach is to put motors at the joints, or if there isn’t room, to put the motors somewhere else and transfer the force using fishing line and pulleys. [Navin Khambhala] chose instead to do it more like the real excavators, with hydraulics using syringes. And we have to admit, the result it pretty elegant in its simplicity.

The syringes do the job of single-acting hydraulic actuators, one at the motor and the other where the force is needed. In between them, what appears to be clear vinyl tubes carry the fluid between syringes. 12 volt DC motors with bolts on them move nuts attached to the syringe pistons to push and pull the pistons. It is so simple that no further explanation is needed, though like most apparently simple things, we’re sure a lot of effort went into making it that way. The video below shows the finished product, as well as walks through the making of it.

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The 4-20 mA Current Loop

The I/O capabilities built into most microcontrollers make it easy to measure the analog world. Say you want to build a data logger for temperature. All you need to do is get some kind of sensor that has a linear voltage output that represents the temperature range you need to monitor — zero to five volts representing 0° to 100°C, perhaps. Hook the sensor up to and analog input, whip up a little code, and you’re done. Easy stuff.

Now put a twist on it: you need to mount the sensor far from the microcontroller. The longer your wires, the bigger the voltage drop will be, until eventually your five-volt swing representing a 100° range is more like a one-volt swing. Plus your long sensor leads will act like a nice antenna to pick up all kinds of noise that’ll make digging a usable voltage signal off the line all the harder.

Luckily, industrial process engineers figured out how to deal with these problems a long time ago by using current loops for sensing and control. The most common standard is the 4-mA-to-20-mA current loop, and here we’ll take a look at how it came to be, how it works, and how you can leverage this basic process control technique for your microcontroller projects.

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Genetically Engineered Muscle Cells Power Tiny Bio-Robots

One of the essential problems of bio-robotics is actuators. The rotors, bearings, and electrical elements of the stepper motors and other electromechanical drives we generally turn to for robotics projects are not really happy in living systems. But building actuators the way nature does it — from muscle tissue — opens up a host of applications. That’s where this complete how-to guide on building and controlling muscle-powered machines comes in.

Coming out of the [Rashid Bashir] lab at the University of Illinois at Urbana-Campaign, the underlying principles are simple, which of course is the key to their power. The technique involves growing rings of muscle tissue in culture using 3D-printed hydrogel as forms. The grown muscle rings are fitted on another 3D-printed structure, this one a skeleton with stiff legs on a flexible backbone. Stretched over the legs like rubber bands, the muscle rings can be made to contract and move the little bots around.

Previous incarnations of this technique relied on cultured rat heart muscle cells, which contract rhythmically of their own accord. That yielded motion but lacked control, so for this go-around, [Bashir] et al used skeletal muscle cells genetically engineered to contract when exposed to light. Illuminating different parts of the muscle ring lets the researchers move the bio-bots anywhere they want. They can also use electric stimulation to control the bio-bots.

The method isn’t quite at the point where home lab biohackers will start churning out armies of bio-bots. But the paper is remarkably detailed in methods and materials, from the CAD files for 3D-printing the forms and bio-bot skeletons to a complete troubleshooting guide. It’s all there, and it could be a game changer for developing the robotic surgeons of the future.

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FabLab Hackathon Gives the Gift of Art Back to a Stranger in Need

If building the James Webb Space Telescope and F/A-18 fighter jets aren’t enough reasons to work for Northrop Grumman, there’s always the FabLab – the company sponsored hackerspace. It’s a place where anything goes and everything is possible, including giving the gift of art back to a stranger in need.

The video below tells the story of [Raul Pizarro], a young man and gifted artist. Diagnosed as a child with muscular dystrophy, [Raul] was getting to the point where the progressive weakening of his muscles was making it difficult to hold up his arm. [Raul]’s art was slipping away – until [Tony Long] caught wind of the story, that is. [Tony] runs the FabLab, and once he put out the word to his colleagues he got a hackathon together to work on solutions for [Raul].

What they came up with was an overhead support system with a tool balancer and custom articulated sling to reduce the effect of gravity and support [Raul]’s arm. To compensate for his reduced range of motion, they also built an easel with actuators that can raise and lower his canvases and position them where he needs them. It looks like the FabLab team paid special attention to making everything as smooth and stable as possible, and as a result [Raul] is back to doing what he does best. Oh, and if [Tony] and the FabLab sound familiar, it might be because he played host when our own [Mike Szczys] visited Northrop last year.

We really like to see hacks that help mankind as a whole, but there’s something special about a bunch of strangers coming together to help just one man too. Hats off to [Tony] and his FabLab team for pulling off a great hack and giving [Raul] back his art.

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