linkage

17 Articles

Piano Escapement Migrates To Drum Kit

June 29, 2026 by 5 Comments

For as popular as the piano is in music studios, homes, and schools, it almost defies logic. Compared to a guitar, harmonica, or drum set, pianos are incredibly complex machines that can have somewhere on the order of 8,000 moving parts in a case that can easily weigh hundreds of pounds and which often responds quite poorly to seasonal changes in temperature and humidity. But for putting up with all of these downsides, musicians are rewarded with an instrument that uniquely responds to touch, style, and emotion. A big reason for that is that mechanical complexity, and [Super Valid Designs] is attempting to bring that design to a drum set.

Compared to the complex machinery that connects the movement of a piano’s key to its hammer striking a string, a kick drum pedal is much simpler. It can only bounce off of the drum or get “buried” where the beater remains pressed up against the drum after hitting it. [Super Valid Designs] wanted something with a bit more finesse and control, so he first 3D printed a mechanism that throws the beater towards the drum head and then disconnects it mechanically from the pedal, so that it rebounds even if the pedal stays depressed. The next steps were more difficult, which involved making sure the mechanism reset itself in a repeatable way, without making too much noise of its own. This involved trying out a few different ideas and printing a massive amount of subtly different linkages, but in the end he’s left with a machine that nearly replicates all of the parts of a piano’s escapement,

The end goal of this project wasn’t simply to reproduce piano mechanisms on a drum set, though. [Super Valid Designs] hopes to make a kick drum that’s much smaller than those found in traditional kits, and since smaller drums respond poorly when the beater remains on or near the drum after striking it, a mechanism like this will dramatically improve the performance of the smaller drum and help reduce the requirement for perfect technique. And, maybe in 50 years or so, these types of escapements will take over the drumming world just like the piano escapement took over keyboards after its invention in the 1700s. Some simpler piano actions have been built before, but the complexity seems to be a requirement for all of the tasks they need to do whether its for a piano or a drum.

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Mobile Coffee Table Uses Legs To Get Around

September 10, 2024 by 22 Comments

For getting around on most surfaces, it’s hard to beat the utility of the wheel. Versatile, inexpensive, and able to be made from a wide array of materials has led to this being a cornerstone technology for the past ten thousand years or so. But with that much history it can seem a little bit played out. To change up the locomotion game, you might want to consider using robotic legs instead. That’s what [Giliam] designed into this mobile coffee table which uses custom linkages to move its legs and get itself from place to place around the living room.

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Screwless Eyeballs Are A Lesson In Design-For-Assembly

June 8, 2024 by 9 Comments

[Will Cogley] makes eyeballs; hey, everyone needs a hobby, and we don’t judge. Like all his animatronics, his eyeballs are wondrous mechanisms, but they do tend toward being a bit complex, especially in terms of the fasteners needed to assemble them.

But not anymore. [Will] redid his eyeball design to be as easy to assemble as possible, and the results are both impressive and instructive. His original design mimics real eyeballs quite well, but takes six servos and a large handful of screws and nuts, which serve both to attach the servos to the frame and act as pivots for the many, many linkages needed. The new design has snap-fit pivots similar to Lego Technic axles printed right into the linkage elements, as well as snap connectors to hold the servos down. This eliminates the need for 45 screws and cuts assembly time from 30 minutes to about six, with no tools required. And although [Will] doesn’t mention it, it must save a bunch of weight, too.

Everything comes at a cost, of course, and such huge gains in assembly ease are no exception. [Will] details this in the video below, including printing the parts in the right orientation to handle the forces exerted both during assembly and in use. And while it’s hard to beat a five-fold reduction in assembly time, he might be able to reduce that even more with a few print-in-place pivots.

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Shake With Your New Robot Hand

December 21, 2021 by 12 Comments

Korean researchers have created a very realistic and capable robot hand that looks very promising. It is strong (34N of grip strength) and reasonably lightweight (1.1 kg), too. There are several videos of the hand in action, of which you can see two of them below including one where the hand uses scissors to cut some paper. You can also read the full paper for details.

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Mechanical 7-segment display

A One-Servo Mechanical Seven-Segment Display

November 13, 2021 by 21 Comments

The seven-segment display may be a bit prosaic after all these years, but that doesn’t mean there aren’t ways to spice it up. Coming up with a mechanical version of the typical photon-based display is a popular project, of which we’ve seen plenty of examples over the years. But this seven-segment display is quite a mechanical treat, and a unique way to flip through the digits.

With most mechanical displays, we’re used to seeing the state of each segment changed with some kind of actuator, like a solenoid or servo. [Shinsaku Hiura] decided on a sleeker design using a 3D-printed barrel carrying one cam for each segment. Each hinged segment is attached to an arm that acts as a follower, riding on its cam and flipping on or off in a set pattern. Which digit is displayed depends on the position of the barrel, which is controlled with a single servo and a pair of gears. It trades mechanical complexity for electrical simplicity and overall elegance, and as you can see from the video below, it’s pretty snappy.

We think the best part of this build is figuring out the shape of the cams. We wonder how they compare to the cam profiles in [Greg Zumwalt]’s mechanical display; it uses two separate discs with grooves, but the principle is pretty much the same.

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Linkage Inferring Software Handwaves Away The Hard Stuff

September 22, 2020 by 17 Comments

Jokes aside, manually designing linkages that move along specific paths is no easy task. Whether we’re doodling paper sketches or constraining lines in a CAD program, we still need to do the work of actually “imagining” the linkage design. If only there were some sort of tool that would do all that hard imagining work for us! Thankfully, we’re in luck! That’s exactly what researchers [Gen Nishida], [Adrien Bousseau2], and [Daniel G. Aliaga1] at Purdue have done. They’ve designed a software tool that lets us position important bodies in space in particular “key” frames, and then the software simply fills in the linkage for you!

To start the design process, the user inputs a few candidate locations that their solid bodies need to reach in the final linkage path.  From here, these locations get fed to a particle filter. This particle filter seeds thousands of semi-random linkage configurations at small timesteps, selects some of the best-matching ones that most closely approximate the required body locations, removes the lesser-scoring results, re-creates a new set of possible joint configurations based on the best matching ones, and repeats until the tool converges on a linkage that respects our input key frames.

Like a brute force search, this solution takes lots and lots of samples to find a solution, but unlike a brute force search, trials iteratively improve, enabling the software to converge closer and closer to a final solution. Under the hood, the software needs to actually simulate these candidate linkage in order to grade them. It’s in this step that the team wrote in additional checks to remove impossible linkages like self-intersecting joints from this linkage “gene pool” before reseeding them. The result is a tool that does all that trial-and-error scratchwork for you–no brain cycles. For more details, have a peek at their (open access!) paper.

Design software that augments our mechanical design capabilities is a rare gem on these pages, and this one is no exception. If your curious to play with other useful linkages simulating tools, have a go at Linkage Designer. And if you’re in the mood for other tools that fill in the blanks, check out this machine learning algorithm that literally fills in footage between frames in a video feed.

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Robot Arms Nudge The Hands Of Time In The Strangest Clock

May 9, 2019 by 8 Comments

We see a lot of clocks here at Hackaday. Digital clocks, retro clocks, lots of Nixie clocks, binary clocks, and clocks that appear to be designed specifically to be unreadable. But this dual-servo kinematic clock is something we haven’t seen yet, and it’s certainly worth a mention.

[mircemk]’s idea is simple and hearkens back to grammar school days when [Teacher] put a large cardboard clock dial on the blackboard and went through the “big hand, little hand” drill. In this case, the static cardboard clock has been replaced by a 3D-printed dial and hands, while a pair of servos linked together by two arms takes the place of the teacher. The video below shows it in action; the joint in the linkage between the two servos has a screw sticking out that can be maneuvered across the clock face to reposition the hands. It’s a little jittery, though; [mircemk] might want to tune the servo loops up a bit or tighten the linkage joints to make things a little smoother.

Even with the shakes, we find it wonderfully weird and hard to stop watching. It reminds us a bit of this luminous plotting clock from a while back – same linkage, different display.

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