A Fast Linear Actuator Entirely In One PCB

There are many ways to make a linear actuator, a device for moving something is a straight line. Most of the easier to make ones use a conventional motor and a mechanical linkage such as a rack and pinion or a lead screw, but [Ben Wang] has gone for something far more elegant. His linear actuator uses a linear motor, a linear array of coils for the motor phases, working against a line of magnets. Even better than that, he’s managed to make the whole motor out of a single PCB. And it’s fast!

This represents something of an engineering challenge, because achieving the required magnetic field from the relatively few turns possible on a PCB is no easy task. He’s done it by using a four-layer board to gather enough turns for the required magnetic field, and a simple view of the board doesn’t quite convey what lies beneath.

PCB motors are perhaps one of those areas where the state of the art is still evolving, and the exciting part is that their limits are being pushed right there in our community. And this isn’t the only linear motor we’ve seen recently either, here’s one used in a model train.

Pikul Servo Powered Falling Dominoes Pushing a Cube

Domino Row Goes With The Flow

Around here, we’re always excited about a new actuator design. Linear actuators are particularly hard to make cheap, fast, and good, so it’s even better when something new that we can build ourselves slides onto the scene.

Researchers at U Penn’s Pikul Research Group took inspiration from the cascade of falling dominoes for an innovative take on linear motion. This article on IEEE Spectrum describes the similarity of the sequential tipping-over with the peristaltic motion of biological systems, including you, swallowing right now.

The motion propagation in falling dominoes, called a Soliton Wave, can be harnessed to push an object at the front of the wave, just like a surfer. See the videos after the break for examples of simple setups that any of us could recreate with laser-cut or 3D printed parts. Maybe you won’t be using them to help a robot swallow (a terrifying idea that the article suggests), but you might need a conveyor or a novel way to help a device crawl like a shrimp. The paper is behind a paywall on IEEE, though you readers likely see enough in the videos to get started, and we can’t wait to see where your dominoes will lead us next.


Sisyphean Ball Race Robot Toils Gracefully, Magnetically

Aren’t ball races and marble runs fun? Wouldn’t they be so much more enjoyable if you didn’t have to climb back up the ladder each time, as it were, and reset the thing? [Johannes] wrote in to tell us about a wee robot with the Sisyphean task of setting a ball bearing on a simple but fun course, collecting it from the end, and airlifting it back to the start of the track.

[Johannes] built this ‘bot to test small-scale resin printing strength as well as the longevity of some tiny linear actuators from Ali that may or may not be available at a moment’s notice. The point was to see how these little guys fared when connected directly to an Arduino or other microcontroller, rather than going the safer route with a motor driver of some kind.

Some things worked well, like the c-clips that keep the axles together, and using quick pulses to release the magnetically-linked ball from the gripper. Other aspects didn’t work out so well. Tiny resin parts do not respond well to force, for starters. And then there’s the actuators themselves. The connections are fragile and the motors are weak, but they vary wildly in quality from piece to piece, so YMMV. Some lose steps, and others occasionally seize. But you wouldn’t know any of that from the graceful movement capture in the video below. Although it appears to be automated, the bot is under remote control because of the motor issues.

Not into ball runs? There are other Sisyphean tasks available, such as moving sand around in the name of meditation.

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3D Printed Linear Actuator Is Cheap And Strong

Motors are all well and good for moving things, but they’re all about the round-and-round. Sometimes, you need to move something back and forth, and for that a linear actuator will do the trick. While they can be readily sourced for under $50 online, [Michael Rechtin] genuinely felt like reinventing the wheel, and managed to whip up a 3D-printed design that costs under 20 bucks.

The basic design is simple, consisting of a small motor which is geared down through several stages using simple spur gears. The last gear in the train is tasked with turning a lead screw which drives the arm of the linear actuator back and forward.

For simplicity, [Michael] used a 24V brushed DC gearmotor for its low cost and the fact it already has a step-down gearbox integrated into the design. It’s paired with a couple more 3D-printed spur gears to provide even more torque. Instead of a fancy lead screw, the build instead just uses a quarter-inch bolt sourced from Home Depot, which can be had much cheaper. This pushes a 3D-printed arm back and forth thanks to a nut stuck in the arm. It’s all wrapped up in a neat-and-tidy 3D-printed housing. The design is able to push with a force of roughly 220 lbs. For a more practical idea of its strength, it can readily crush an empty soda can.

The video on the design is great, showing how important features like limit switches are added, and how the wiring can be neatly hidden away inside the housing. We’ve seen [Michael’s] work before, too, like strength testing various types of 3D printed gears. Video after the break.

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The end result - motorized window in a silver stainless steel frame, with the linear actuators and gas struts, shown from the outside half-open.

Swing Gate Motors Come To Help For Opening A Giant Servery Window

[Martin Roberts] wrote to us, telling us about a build that his company, [Ocean View Workshop], was tasked with. Creating a four meter wide window able to open vertically is no small feat, and it had to be custom-built because the local company building such windows wasn’t comfortable working with anything other than aluminum — insufficient for the window’s scale. With massive weight of the glass alone, structural requirements for supporting it, and the mechanical loads to be applied, some careful planning was in order.

To start with, this window had to be motorized, as an average person wouldn’t be capable of pulling it upwards. Not satisfied with the linear actuator choice available, they went to a hardware store and found some swing gate actuators that, in workshop tests, proved themselves to be more than capable of handling way over the weight required. In fact, they were capable of lifting [Martin] himself off the ground without much hassle.

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Building A High-Capacity Linear Servo Actuator

Linear actuators are useful things, moving things in straight lines rather than annoying circles like so many motors. [Retsetman] recently built a linear servo actuator of his own design with accurate positional control.

The design relies on a carriage that moves along a threaded rod, perhaps the most rudimentary design of linear actuator. A large brushed DC motor is used to turn the threaded rod through a 3D-printed 9:1 herringbone geartrain, shifting the actuator back and forth. End stop switches are used to disengage the motor to avoid damage to the mechanism. Feedback is via a ten-turn potentiometer driven off the output geartrain to match the range of the actuator to the rotational range of the pot.

The final build has a stroke of approximately 100 mm, and can lift and hold a 15 kg weight with ease. In a pull test, the actuator failed at a load just shy of 100 kg. If you’re looking for something smaller, though, you can try building a linear actuator out of old DVD drive parts instead. Video after the break.

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1960s Stereo Console Gets An Upgrade

Faced with an old console stereo from the 1960s that was barely functional, [Sherman Banks] aka W4ATL decided to upgrade its guts while keeping its appearance as close to the original as possible. This stereo set is a piece of mahogany furniture containing an AM/FM stereo receiver and an automatic turntable from JCPenny’s Penncrest line. As best [Sherman] can determine, it is most likely a 1965 model. The old electronics were getting more and more difficult to repair and the tuner was drifting off-station every 15 minutes. He didn’t want to throw it away, so he decided to replace all the innards.

The first thing was to tear out the old electronics while retaining the chassis proper. The new heart of the entertainment center is a modern Denon AV stereo receiver. This unit can be controlled over Ethernet, has a radio tuner, inputs for SiriusXM and a turntable, and supports Bluetooth streaming. [Sherman] next replaced the 1965 turntable, and then turned his attention to connecting up the controls and indicators.

The potentiometers were replaced with equivalent ones of lower resistance, the neon stereo indicator was replaced with an LED, but the linear tuning dial proved to be a nearly two month challenge and resulted in a cool hack. In brief, he connected an optical rotary encoder to the tuning knob and used a stepper motor with a linear actuator to control the dial indicator. All this is controlled from an Arduino Mega 2560 with three shields for I/O and LAN. But there was still one remaining issue — without vacuum tubes to warm up, the radio would play immediately after power-on. [Sherman] fixed that by programming the Arduino to slowly ramp up the volume at the same rate as the original tube receiver. And finally, he installs a small HDMI monitor in the corner to display auxiliary information and metadata from the Denon receiver.

Check out the videos below the break. We wrote about a couple of similar conversions in the past: this one from 2018 was also a Penncrest, and from last year this COVID isolation project that emphasized the addition of a new liquor cabinet.

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