Stewart platform

15 Articles

Stewart Platform Walker Gains Feeling In Legs From Resistors

August 1, 2026 by 1 Comment

Stewy is a very interesting robot, with some slightly odd kinematics. Its head is a Stewart platform, which is a common-enough 6-DOF actuated plate normally used with a fixed base. By connecting legs to the same servos running the Stewart platform, [JD] turned it into an adorable hexapod walker. The walker had a problem, though: it can’t feel its feet, and [JD] thinks that would make it much more mobile on uneven surfaces. So he got some resistors to turn the cheap servos in its legs into force-sensing actuators.

Well, almost. He’s not actually putting strain gauges or anything like that into the legs; he’s just measuring the voltage drop across a resistor in series with the servos. Since the motors draw more current the more torque they’re putting out, he has a very quick and easy way to sense the current and thus the torque using good old Ohm’s law and an analog input on the microcontroller driving the robot. It’s a simple hack, but the data he’s getting is surprisingly good for how much work it is to add to a robot, as you can see in the video — at least once he slowed down the servos a touch.

Perhaps this isn’t a ground-breaking innovation, but [JD] does a very good idea explaining it. Of course if you want to use resistors to sense force directly, force-sensitive resistors are a thing that we’ve seen in everything from Twister-mat MIDI controllers to self-leveling 3D printers.

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3D Mouse With 3D Printed Flexures And PCB Coils

January 31, 2024 by 7 Comments

3D mice with six degrees of freedom (6DOF) motion are highly valued by professional CAD users. However, the entry-level versions typically cost upwards of $150 and are produced by a single manufacturer. [Colton Baldridge] has created the OS3M Mouse — an open source alternative using PCB coils and 3D printed flexures.

The primary challenges in creating a 6DOF input device, similar to the 3Dconnexion Space Mouse, lie in developing a mechanical coupling that enables full range motion, and electronics capable of precisely and consistently measuring this motion. After several iterations of printed flexure combinations and trip down the finite element analysis (FEA) rabbit hole, [Colton] had a working single-piece mechanical solution.

To measure the knob’s movement accurately, [Colton] employs inductive sensing. Inductance to Digital Converters (LDCs) assess the inductive alterations across three pairs of PCB coils, each having an opposing metal disk mounted on the knob. This setup allows [Colton] to use a Stewart platform‘s kinematic model calculate the  knob’s relative position. The calculation are done on an STM32 which also acts USB HID send the position data to a computer. For the demo [Colton] created a simple C++ app to translate the position data to Solidworks API calls.

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Stewart Platform Keeps Its Eye On The Ball

January 4, 2023 by 4 Comments

Although billed as a balancing robot, [Aaed Musa’s] robot doesn’t balance itself. It balances a ball on a platform. You might recognize this as something called a Stewart platform, and they are great fun at parties if you happen to party with a bunch of automation-loving hackers, that is. Take a look at the video below to see the device in action.

If you want to duplicate the project, there’s a bit of expense, but the idea behind it is explained in the video. Much of the robot is 3D printed with threaded inserts. Even the ball is 3D printed in two parts along with a cubic connector to hold the two hemispheres together. The acrylic platform was cut with a water jet, although you could just as easily have cut it with hand tools.

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Stewart Platform Wields Magic Fingers To Massage Your Scalp

August 4, 2022 by 13 Comments

Attention Hackaday editors: We on the writing crew hereby formally request budget allocation for installing a Stewart platform head massager on the chair of each workstation in the secret underground writer’s bunker. We think the benefits that will accrue thanks to reduced stress alone will more than justify the modest upfront costs. Thank you for your consideration.

OK, maybe that request is going nowhere, but having been on the receiving end of these strangely relaxing springy scalp stimulators, we can see where [David McDaid] was going with this project. As he clearly states up front, this is a ridiculously over-engineered way to get your scratchies on, but there’s very little not to love about it. Stewart platforms, which can position a surface with six degrees of freedom and range in size from simple ball balancers to full-blown motion simulators, are fascinating devices, and we can’t think of a better way to learn about them than by building one.

Like all Stewart platforms, [David]’s is mechanically simple but kinematically complicated, and he takes great pains to figure out all the math and explain it in an approachable style. The device is mounted with the end-effector pointed down, allowing the intended massagee to insert their noggin into the business end and receive the massage pattern of their choice. Looking at the GIFs below, it’s easy to see why [David] favors the added complexity of a Stewart, which makes interesting patterns like “The Calmer” possible. They’re all intriguing, although the less said about “The Neck Breaker” the better, we’d say.

Hats off (lol) to [David] for this needless complex but entertaining build.

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An Interesting Circular Stewart Platform

June 10, 2022 by 9 Comments

Stewart platforms are pretty neat, and not seen in the wild all that often, perhaps because there aren’t a vast number of hacker-friendly applications that need quite this many degrees of freedom within such a restricted movement range. Anyway, here’s an interesting implementation from the the curiously named [Circular-Base-Stewart-Platform] YouTube channel (no, we can’t find the designer’s actual name) with a series of videos from a few years ago, showing the construction and operation of such a beast. This is a very neat mechanism comprised of six geared motors on the end of arms, engaging with a large internal gear. The common end of each arm rides on the central shaft, each with its own bearing. With the addition of the usual six linkages, twelve ball joints, and a few brackets, a complete platform is realised.

This circular arrangement is so simple that we can’t believe we haven’t come across it before. One interesting deviation from the usual Stewart platform arrangement is the use of a central slip-ring connector to provide power, allowing the whole assembly to rotate continuously, in addition to the usual six degrees of freedom the mechanism allows. Control is courtesy of an Arduino Pro Mini, which drives the motors using a handful of Pololu TB6612 (PDF) dual H-bridge driver modules. Obviously, the sketch running on the Arduino will give the thing a fixed motion, but add in an additional data link over that central slip-ring setup (or maybe a wireless link), and it will be much more useful.

We recently saw another 6-DOF actuator design, using flexures, yet another ball-balancing hack, but if you want an actually useful Stewart platform application, checkout this pool-playing robot!

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Flexures Make This Six-DOF Positioner Accurate To The Micron Level

May 6, 2022 by 26 Comments

It’s no secret that we think flexures are pretty cool, and we’ve featured a number of projects that leverage these compliant mechanisms to great effect. But when we saw flexures used in a six-DOF positioner with micron accuracy, we just had to dig a little deeper.

The device is known as the Hexblade, and it comes to us from the lab of [Jonathan Hopkins] at UCLA. We have to admit that at times, the video below feels a little like the “Turbo Encabulator” schtick — “three identical decoupled actuation limbs arranged in an axisymmetric configuration” may be perfectly descriptive, but it does not flow trippingly from the tongue. Hats off to [Professor Hopkins] for nailing the narration, though, and really, once you get a handle on the jargon, it all makes perfect sense. The platform is supported by a total of six flexures, which look like bent pieces of sheet metal but are actually cut from a solid block of material using wire EDM. Three of the flexures are oriented in the plane of the platform, while the other three are perpendicular to it. The far end of each flexure is connected to a voice-coil actuator that is surrounded by another flexure, this one in a parallelogram arrangement. The six actuators can move the platform smoothly through three linear translations (X, Y, and Z) and three rotations (roll, pitch, and yaw).
The platform’s range of motion is limited, but the advantages of using flexures as bearings are clear — there’s no backlash or hysteresis, and the voice coils can control the position of the stage to micron accuracy. Something like the Hexblade would be an ideal positioner for microscopy, and we can imagine an even smaller version, perhaps even a MEMS-fabricated one for nanomanufacturing applications. The original concept of the Hexblade serving as the print head for a fabrication robot for space applications is pretty cool, too, and we’d venture to say that a homebrew version of this probably isn’t out of reach either.

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Robotic Pool Cue Can Be Your Friend Or Your Foe

February 24, 2021 by 21 Comments

In his everlasting quest to replace physical skill with technology, [Shane] of [Stuff Made Here] has taken aim at the game of eight-ball pool. Using a combination of computer vision and mechatronics, he created a robotic pool system that can allow a physical game of pool over the internet, or just beat human players. See the video after the break.

Making a good pool shot requires three discrete steps. First, you need to identify the best shot, then figure out how exactly to strike the balls to achieve the desired results, and finally physically execute the shot accurately. [Shane’s] goal was to automate all these steps. For the physical part, he built a pool cue with a robotic tip which only requires the user to place in approximately the right position, while a pneumatic piston mounted on a Stewart platform does the rest. A Stewart platform is a triangular plate mounted with six reciprocating rods, which gives it the required freedom of motion. The rods’ bases are attached to a set of cranks actuated by tension cables pulled by servos mounted at the rear-end of the cue. An adjustable air system allows the power of the shot to be adjusted as required.

A camera mounted is mounted over the table and connected to computer vision software to gather the required position information. Fiducials on the corners of the table and the cue tip allow the position of the pockets, balls, and cue to be accurately determined, and theoretically should allow the robot to take the perfect shot. Getting this to work in reality quickly turned into a very frustrating experience. After many hours of debugging, [Shane] tracked the error to a tiny forgotten test function that was introducing 5-10 mm of position error, and 2 of the six servos in the cue not performing up to spec. To determine the vertical positioning of the cue, an IMU and fixed height foot were added. [Shane] also added an overhead projector to overlay all required information directly on the table. Continue reading “Robotic Pool Cue Can Be Your Friend Or Your Foe” →