Cube Teeter Totter: One Motor, Many Lessons

June 16, 2025 by Matt Varian 5 Comments

Balancing robots are always fun to see, as they often take forms we’re not used to, such as a box standing on its corner. This project, submitted by [Alexchunlin], showcases a cool single motor reaction cube, where he dives into many lessons learned during its creation.

At the outset, [Alexchunlin] thought this would be a quick, fun weekend project, and while he achieved that, it took longer than a weekend in the end. The cube’s frame was a simple 3D print with provisions to mount his MotorGo AXIS motor controller. This motor controller was initially designed for another project, but it’s great to see him reuse it in this build.

Once the parts were printed and assembled, the real work began: figuring out the best way to keep the cube balanced on its corner. This process involved several steps. The initial control code was very coarse, simply turning the motor on and off, but this didn’t provide the fine control needed for delicate balancing. The next step was implementing a PID control loop, which yielded much better results and allowed the cube to balance on a static surface for a good amount of time. The big breakthrough came when moving from a single PID loop to two control loops. In this configuration, the PID loop made smaller adjustments, while another control loop focused on the system’s total energy, making the cube much more stable.

By the end of the build, [Alexchunlin] had a cube capable of balancing in his hand, but more importantly, it was a great learning experience in controls. Be sure to visit the project page for more details on this build and check out his video below, which shows the steps he took along the way. If you find this project interesting, be sure to explore some of our other featured reaction wheel projects.

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Two rings of magnets are shown encasing a circular channel in a white plastic piece. The channel is filled with liquid metal, and a loop of wire is about to be lowered into the metal.

Magnetohydrodynamic Motors To Spin Satellites

May 18, 2025 by Aaron Beckendorf 18 Comments

Almost all satellites have some kind of thrusters aboard, but they tend to use them as little as possible to conserve chemical fuel. Reaction wheels are one way to make orientation adjustments without running the thrusters, and [Zachary Tong]’s liquid metal reaction wheel greatly simplifies the conventional design.

Reaction wheels are basically flywheels. When a spacecraft spins one, conservation of angular momentum means that the wheel applies an equal and opposite torque to the spacecraft, letting the spacecraft orient itself. The liquid-metal reaction wheel uses this same principle, but uses a loop of liquid metal instead of a wheel, and uses a magnetohydrodynamic drive to propel the metal around the loop.

[Zach] built two reaction wheels using Galinstan as their liquid metal, which avoided the toxicity of a more obvious liquid metal. Unfortunately, the oxide skin that Galinstan forms did make it harder to visualize the metal’s motion. He managed to get some good video, but a clearer test was their ability to produce torque. Both iterations produced a noticeable response when hung from a string and activated, and achieved somewhat better results when mounted on a 3D-printed air bearing.

Currently, efficiency is the main limitation of [Zach]’s motors: he estimates that the second model produced 6.2 milli-newton meters of torque, but at the cost of drawing 22 watts. The liquid metal is highly conductive, so the magnetohydrodynamic drive takes high current at low voltage, which is inconvenient for a spacecraft to supply. Nevertheless, considering how hard it is to create reliable, long-lasting reaction wheels the conventional way, the greatly improved resilience of liquid-metal reaction wheels might eventually be worthwhile.

If you’re curious for a deeper look at magnetohydrodynamic drives, we’ve covered them before. We’ve also seen [Zach]’s earlier experiments with Galinstan.

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Building A Small Gyro Stabilized Monorail

August 27, 2024 by Lewin Day 12 Comments

Monorails aren’t just the core reason why The Simpsons remains on air after thirty-six seasons, twenty-six of which are unredeemable garbage. They’re also an interesting example of oddball rail travel which has never really caught on beyond the odd gadgetbahn project here and there. [Hyperspace Pirate] recently decided to investigate the most interesting kind of monorail of all—the gyro stabilized type—on a small scale for our viewing pleasure.

The idea of a gyro-stabilized monorail is to use active stability systems to allow a train to balance on a single very thin rail. The benefits of this are questionable; one ends up with an incredibly expensive and complex rail vehicle that must always run perfectly or else it will tip over. However, it is charming to watch in action.

[Hyperspace Pirate] explains how the monorail vehicle uses control moment gyroscopes to keep itself upright. The video also explains the more common concept of reaction wheels so the two systems can be contrasted and compared. It all culminates in a wonderful practical demonstration with a small 3D printed version of a 20th-century gyro monorail running on a 24″ track.

If you’re studying mechanical engineering this is a great project to pore over to see theoretical principles put into obvious practice. Video after the break.

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Rocket Mounted 3D Printed Camera Wheel Tries, Succeeds, And Also Fails

December 6, 2022 by Ryan Flowers 29 Comments

[Joe] at BPS.space has a thing for rockets, and his latest quest is to build a rocket that will cross the Kármán Line and launch into the Final Frontier. And being the owner of a YouTube channel, he wants to have excellent on-board video that he can share. The trouble? Spinning. A spinning rocket is a stable rocket, especially as altitude increases. So how would [Joe] get stable video from a rocket spinning at several hundred degrees per second? That’s the question being addressed in the video below the break.

Rather than use processing power to stabilize video digitally, [Joe] decided to take a different approach: Cancelling out the spin with a motor, essentially making a camera-wielding reaction wheel that would stay oriented in one direction, no matter how fast the rocket itself is spinning.

Did it work? Yes… and no. The design was intended to be a proof of concept, and in that sense there was a lot of success and some excellent video was taken. But as with many proof of concept prototypes, the spinning camera module has a lot of room for improvement. [Joe] goes into some details about the changes he’ll be making for revision 2, including a different motor and some software improvements. We certainly look forward to seeing the progress!

To get a better idea of the problem that [Joe] is trying to solve, check out this 360 degree rocket cam that we featured a few years ago.

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Can You Cheat At Tightrope Walking?

June 18, 2022 by Dave Rowntree 14 Comments

Tightrope walking is no mean feat — it takes years to master (even with a balance rod) — but that’s too much like hard work for [James Bruton]. Obviously, the solution is just a matter of the application of some electronically-controlled balancing technology, and [James] is just the guy for the job. Bearing a passing resemblance to a cross between a prop from Ghostbusters and a medieval torture device, this weighty balancing cheat device almost kind of works!

On a slightly more serious note, bipedal balance is a complex problem to solve. You have multiple limb sections, which can move independently in many ways, as well as the upper body also contributing to shifting around the center of gravity in a hard-to-predict way. So it’s no great surprise that a simple torque reaction device strapped to the torso doesn’t help a great deal, but it sure is fun to watch him trying. The bottom line is this — our bodies are pretty heavy, and the amount of force needed to correct tilt in the plane of interest is hard to generate without the reaction wheel itself being really heavy, and that extra mass doesn’t exactly help with the overall balancing problem. We reckon the overall concept is sound, it’s just that all those extra limbs flopping around make this simplistic sensing and compensation strategy only partly effective.

Stabilizing small robots is probably a bit easier than a human, such as this gyroscopically-stabilized monowheel, but sometimes you don’t even need the gyroscope, as you can control the driving wheels directly.

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Quick Reaction Saves ESA Space Telescope

October 22, 2021 by Roger Cheng 5 Comments

Once launched, most spacecraft are out of reach of any upgrades or repairs. Mission critical problems must be solved with whatever’s still working on board, and sometimes there’s very little time. Recently ESA’s INTEGRAL team was confronted with a ruthlessly ticking three hour deadline to save the mission.

European Space Agency INTErnational Gamma-Ray Astrophysics Laboratory is one of many space telescopes currently in orbit. Launched in 2002, it has long surpassed its original designed lifespan of two or three years, but nothing lasts forever. A failed reaction wheel caused the spacecraft to tumble out of control and its automatic emergency recovery procedures didn’t work. Later it was determined those procedures were dependent on the thrusters, which themselves failed in the summer of 2020. (Another mission-saving hack which the team had shared earlier.)

With solar panels no longer pointed at the sun, battery power became the critical constraint. Hampering this time-critical recovery effort was the fact that antenna on a tumbling spacecraft could only make intermittent radio contact. But there was enough control to shut down additional systems for a few more hours on battery, and enough telemetry so the team could understand what had happened. Control was regained using remaining reaction wheels.

INTEGRAL has since returned to work, but this won’t be the last crisis to face an aging space telescope. In the near future, its automatic emergency recovery procedures will be updated to reflect what the team has learned. Long term, ESA did their part to minimize space debris. Before the big heavy telescope lost its thrusters, it had already been guided onto a path which will reenter the atmosphere sometime around 2029. Between now and then, a very capable and fast-reacting operations team will keep INTEGRAL doing science for as long as possible.

A Self-Driving Bicycle Is Something To Marvel At

June 10, 2021 by Lewin Day 44 Comments

One of the most annoying things about bicycles is that they don’t stay up on their own, especially when they’re stationary. That’s why they come with stands, after all. That said, if you had plenty of advanced electronic and mechanical equipment fitted to one, you could do something about that, and that’s just what [稚晖君] did.

The video of the project comes without subtitles or any translation, but the gist of it is this. A reaction wheel is fitted to the seat tube, along with a motor which can turn the handlebars via a linkage attached to the head stem. There’s also a motor to drive the bicycle forward via a friction drive to the rear wheel. Combine these with an inertial measurement unit and suitable control system, and you have a bike that can balance while standing perfectly still.

The performance of the system is impressive, and is even able to hold the bike perfectly upright while balanced on a fence rail. Thanks to an onboard camera and LIDAR system, the bike can also drive itself around with no rider on board, which is quite a spooky image. Find a way to do the same while hiding the extra mechanics and you’d have one hell of a Halloween display.

Similar projects have been attempted in the past; we featured a self-balancing bike built as a university project back in the distant past of 2012. Video after the break.

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