Autonomous Coin Flipper Flips Expensive Coin

April 22, 2026 by Zoe Skyforest 27 Comments

[Térence Grover] had a very special coin—a €1,000 commemorative piece only available to Monégasque nationals. If you want to flip one, normally you’d have to go snatch one up from somebody in Monaco—or you could just do it online!

Yes, he built an automated online coin flipper to flip this very special piece of coinage. A 12-volt solenoid is fired to flip the coin into the air. It then lands on its 3D-printed tray, where a Raspberry Pi-based computer vision system built with OpenCV and a TFLite model classifies whether the result is heads or tails via a machine learning algorithm. An iris mechanism operated by servo motor then centers the coin on the tray, so it sits back over the solenoid, ready to flip once again. [Térence] was eventually able to refine this simple homemade build to the point that it ran autonomously for a full 50,000 flips on a livestream without issue.

The mechanism in this build is not dissimilar to a coin flipper we’ve seen before. We’ve also explored the statistics involved, too. Video after the break.

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Electric Wind-Up Plane Uses Supercapacitors For Free Flight Fun

April 18, 2026 by Tyler August 21 Comments

There’s something to be said for a simple wind-up, free flight model airplane. With no controls, it must be built very well to fly well, and with only the limited power of a rubber band, it needs a good, high-lift design without much superfluous drag to maximize flight time. There’s also something to be said for modernity though, and prolific hacker [Tom Stanton] puts them together with this supercapacitor plane.

If that sounds familiar, it’s because [Tom] did this before back in 2023. But for that first attempt he converted a commercial R/C toy rather than a plane optimized for low-power free flight. Just like with the best rubber-band machines, his goal for the new production is more flight time than winding time. Plus lots of views on YouTube, but that goes without saying.

Thus this machine is smaller and lighter than the previous iteration. Rather than balsa and tissue like the free-flight aircraft of our youths, [Tom] is using 3D printed plastic for the structure. But he’s got a neat hack built in: he’s printing the wings and control surfaces directly onto tissue paper, eliminating the bonding step. Of course that means his wings are printed flat, but a bit of heat and some bending and he has a single-surface airfoil. Single-surface airfoils are normal in this application, anyway: closed wings add too much weight for too little gain. If you want to try the technique, he’s got files on Printables.

Another interesting factoid [Tom] discovered is that the energy density of supercapacitors decreases sharply below 10 F. As you might imagine by the square-cubed law, bigger is better, but the sharp drop-off dictated he use a single 10 F cap for this build, along with a micro motor. Using the wind-up generator from his previous build, he’s able to get 45 seconds of flight out of just 4 seconds of cranking, a good ratio indeed.

[Tom] seems to like playing with different ways to power his toys; aside from supercapacitors, we’ve also seen him finessing aircraft air motors — including an attempt at a turbine for a model helicopter.

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Building A Big RC Mini Truck

April 16, 2026 by Zoe Skyforest 3 Comments

Kei trucks are some of the smallest commercial vehicles out on the roads today. You can also get lots of cute kei RC cars if you’re into the toy side of things. [Victor] wanted to split the difference with Truck-Kun, and built a 1:3 scale kei truck to show off at a recent anime convention.

The truck is modelled on the Suzuki Carry.

The build started with a classic hacker favorite—a bunch of old hoverboard motors. These brushless hub motors are pretty easy to drive and have plenty of torque right out of the box. A simple ladder frame was whipped up with a hoverboard wheel at each corner, with a body whipped up out of cardboard, paint, and a few 3D printed parts to hold everything together.

Steering was courtesy of a leadscrew and stepper motor from an old 3D printer. RP2040s were thrown in to talk to the motor controllers, while an ESP32-S3 was charged with communicating with an Xbox One controller to receive directional commands.

It was a neat build that stood tall over most any other kei RC car at Anime Los Angeles. Only, it ended in tears when the 100-pound machine accidentally drove at full throttle into a wall and smashed itself to pieces. Still, that’s just an excuse for [Victor] to build a better one for next year.

We love a good RC build around these parts, and we love kei trucks too.

A model submarine is shown on a dock. The body of the submarine is made out of a series of acrylic tubes, with other parts made out of grey plastic.

3D-Printed Parts Nearly Sink RC Submarine

April 13, 2026 by Aaron Beckendorf 23 Comments

Of all the remote-control vehicles one can build, a submarine is possibly the hardest: if something goes wrong with almost any other vehicle, it’s easy to recover and repair, but a submarine is a very different affair. This nearly lost [James] of [ProjectAir] his latest project, a 2.7-meter long RC submarine, but it survived to make a few test sails.

Before building the full version, [James] made a test prototype. These submarines use large syringes as ballast tanks, pulling water in and out of the submarine body. The plungers are driven by a lead screw, and have a linear potentiometer for feedback. This can be wired in the same way as a servo motor, making it compatible with the RC controller. The controller receives its signal from an antenna in a buoy tethered to the submarine. Since initial tests worked well, [James] moved on to the full-scale model.

This was made out of radially-arranged acrylic tubes, with all but the top tube left open to the water. At the back of the submarine there were servo-actuated fins and a propeller, which would allow it to steer, ascend, and descend underwater. To waterproof the servo motors, [James] sealed them as much as possible, then filled them with oil. The other water-exposed electronics were either potted in epoxy or coated with a waterproofing compound. During testing, the submarine descended without issue, but was reluctant to resurface. Most of the external components had been 3D printed, and water infiltrated the infill below a certain depth. [James], however, managed to recover it before it was permanently lost, and managed to make a few other dives at a very limited depth.

On the other end of the spectrum from an RC submarine, we’ve also seen a rubber band-powered submarine. We’ve also seen a smaller, but more dive-ready RC submarine. Continue reading “3D-Printed Parts Nearly Sink RC Submarine” →

Teardown Of A 2026 LEGO SMART Brick

March 18, 2026 by Maya Posch 46 Comments

LEGO SMART brick from its side. (Credit: EvilmonkeyzDesignz, YouTube)

At the beginning of March this year LEGO released their new SMART brick, which looks like a 2×4 stud brick and is filled to the brim with sensors, LEDs, NFC and Bluetooth functionality, as well as a purported custom ASIC. The central idea behind it appears to be to add a lot of interactivity to LEGO builds while allowing for mesh-style communication with other SMART bricks. Naturally, this makes it a great subject for a teardown, which is what [EvilmonkeyzDesignz] over on YouTube did in a recent video.

Normally the only way you can purchase one of these new bricks is by buying them as part of a ‘Smart Play’ set, but someone was selling singular bricks on EBay. As the brick is inductively recharged, it’s pretty well-sealed, requiring a fairly destructive opening method.

Directly below the transparent top is a speaker, with the opposing PCB on the main body containing a microphone as well as a number of RGB LEDs. On the opposite side of this PCB we find the photo sensor, but to get to this part of the PCB the copper wires that wrap around the entire main assembly have to be disconnected from the PCB’s side pads with some force as they’re apparently pressed in place without the use of solder.

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LEGO Machine Plays Tic-Tac-Toe Without Electronics

March 16, 2026 by Zoe Skyforest 10 Comments

Tic-Tac-Toe is a relatively simple game, and one of the few which has effectively been solved for perfect play. The nature of the game made it possible for [Joost van Velzen] to create a LEGO machine that can play the game properly in an entirely mechanical fashion.

The build features no electronics to speak of. Instead, it uses 52 mechanical logic gates and 204 bits of mechanical memory to understand and process the game state and respond with appropriate moves in turn. There are some limitations to the build, however—the game state always begins with the machine taking the center square. Furthermore, the initial move must always be played on one of two squares—given the nature of the game though, this doesn’t really make a difference.

It’s also worth heading over to the Flickr page for the project just to appreciate the aesthetics of the build. It’s styled in the fashion of an 18th-century automaton or similar. It’s also been shared on LEGO Ideas where it’s raised quite a profile.

If you’ve ever wanted to think about computing in a mechanical sense, this build is a great example of how it can be done. We often see some fun LEGO machines around these parts, from massive parts sorters to somewhat-functional typewriters.

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Making A Bladeless Tesla Turbine Generator In LEGO

March 13, 2026 by Maya Posch 2 Comments

The Tesla turbine is a bladeless centripetal-flow turbine invented by Nikola Tesla in 1913, using the boundary-layer effect rather than having a stream of gases or a fluid impinge on blades. Recently [Jamie’s Brick Jams] constructed one using LEGO to demonstrate just how well these turbines work compared to their bladed brethren.

Since it uses the boundary-layer effect, the key is to have as much surface area as possible. This means having many smaller discs stacked side by side with some spacing between them.

Interestingly, the air that is directed against the turbine will travel inwards, towards the axle of the discs and thus requiring some way to vent the air. In the video a number of design prototypes are tested to see how they perform before settling on a design suitable for a functional generator.

The first discs are printed in PLA with an FDM printer, which are put on a shaft with 1 mm spacers. What becomes clear during testing is that these turbines can reach ridiculous speeds, but torque is really quite weak until you hit very high RPMs, well beyond 10,000 RPM. This is a bit of an issue if you want to drive any load with it, especially on start-up, but managed to propel a walker robot as a quick torque test.

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