Saber 2 is a 3D-printed gear-and-cam saber-toothed tiger that can be motorized to show an excellent loping movement. It’s 14” long and 10” tall and consists of 108 components of which 34 are unique parts, and it all moves with the help of a 6 VDC 60 RPM gearmotor. With threaded PLA rods to keep it all together, and tapped holes to secure the rods, one imagines the printer would have to be pretty finely tuned and leveled for the parts to move as elegantly as you see in the video.
3D printers are great for creating static objects, but if you’re clever, it’s possible to print functional devices. If you’re absolutely brilliant you can go far beyond that, which is the case here. This door handle with a key-code lock does it all with 3D printing using mechanism designs that look like alien technology. This is just one application of a much more interesting mechanical digital logic they’re developing (PDF).
Working from the [Hasso-Plattner-Institut], the research team is focusing on metamaterials as mechanisms in and of themselves. The crux of this lock is a series of bistable springs that — if the correct code is entered — will trigger in series to unlock the door. The project builds on the grid of shearing cells seen in the door handle we featured last year. It happens quickly in the video, but the intricate cascade of the handle unlocking is a treat to witness.
It’s a fascinating show of mechanical design. The common elements of digital electronics are all present: set or unset bits, logic gates, propagation issues, the whole works. But there are added challenges in this system, like the need for special cells that can turn the logic chain by 90 degrees and split the signal into more than one part.
This signal splitting is seen in the upper right (bifurcation) and leads into what is in effect an amplifier. The locking bolt must be moved twice the distance of a normal cell, so a dual-cell input is necessary to offset the loss of force from the incoming smaller cells. Cognitively we understand this, but we’re still trying to gain an intuitive sense of the amplifer mechanism.
One thing’s for sure, the overall concept is far cooler than this admittedly awesome door lock mechanism. The paper is worth your time for a deep dive. It mentions their design editor software. You can play with it online but we don’t think it’s been updated to include the new logic cells yet.
The four bar linkage is a type of mechanical linkage that is used in many different devices. A few examples are: locking pliers, bicycles, oil well pumps, loaders, internal combustion engines, compressors, and pantographs. In biology we can also find examples of this linkage, as in the human knee joint, where the mechanism allows rotation and keeps the two legs bones attached to each other. It is also present in some fish jaws that evolved to take advantage of the force multiplication that the four bar mechanism can provide.
How It Works
The study of linkages started with Archimedes who applied geometry to the study of the lever, but a full mathematical description had to wait until the late 1800’s, however, due to the complexity of the resulting equations, the study and design of complex linkages was greatly simplified with the advent of the digital computer.
Mechanical linkages in general are a group of bodies connected to each other to manage forces and movement. The bodies, or links, that form the linkage, are connected to each other at points called joints. Perhaps the simplest example is the lever, that consists of a rigid bar that is allowed to pivot about a fulcrum, used to obtain a mechanical advantage: you can raise an object using less force than the weight of the object.
Two levers can be connected to each other to form the four bar linkage. In the figure, the levers are represented by the links a (A-D) and b (B-C). The points A and B are the fulcrum points. A third link f (C-D) connects the levers, and the fourth link is the ground or frame g (A-B) where the mechanism is mounted. In the animation below, the input link a (the crank) performs a rotational motion driving the rocker rod b and resulting in a reciprocating motion of the link b (the rocker).
This slider-crank arrangement is the heart of the internal combustion engine, where the expansion of gases against a sliding piston in the cylinder drives the rotation of the crank. In a compressor the opposite happens, the rotation of the crank pushes the piston to compress the gas in the cylinder. Depending on how the mechanism is arranged, it can perform the following tasks:
- convert rotational motion to reciprocating motion, as we just discussed above.
- convert reciprocating motion to rotational motion, as in the bicycle.
- constrain motion, e.g. knee joint and car suspension.
- magnify force, as in the parrotfish jaw.
One interesting application of the four bar linkage is found in locking pliers. The B-C and C-D links are set at an angle close to 180 degrees. When force is applied to the handle, the angle between the links is less than 180 (measured from inside the linkage), and the resulting force in the jaws tries to keep the handle open. When the pliers snap into the locked position that angle becomes less than 180, and the force in the jaws keeps the handle in the locked position.
In a bicycle, the reciprocating motion of the rider´s legs is converted to rotational motion via a four bar mechanism that is formed by the two leg segments, the bicycle frame, and the crank.
As with many other inventions of humankind, we often find that nature has already come up with the same idea via evolution. The parrotfish lives on coral reefs, from which it feeds, and has to grind the coral to get to the polyps inside. For that job, they need a very powerful bite. The parrotfish obtains a mechanical advantage to the muscle force by using a four bar linkage in their jaws! Other species also use the same mechanism, one is the Moray eel, shown in the image, which has the very particular ability to launch its jaws up in the mouth to capture its prey, much like the alien from the film series.
The joints connecting the links in the linkage can be of two types. A hinged joint is called a revolute, and a sliding joint is called a prismatic. Depending on the number of revolute and prismatic joints, the four bar linkage can be of three types:
- Planar quadrilateral linkage formed by four links and four revolute points. This is shown in the animation above.
- Slider-crank linkage, formed by three revolute joints and a prismatic joint.
- Double slider formed by two revolute joints and two prismatic joints. The Scotch yoke and the trammel of Archimedes are examples.
There are a great number of variations for the four bar linkage, and as you can guess, the design process to obtain the forces and movements that we need is not an easy task. An excellent resource for the interested reader is KMODDL (Kinematic Models for Design Digital Library) from Cornell University. Other interesting sites are the 507 mechanical movements, where you can find nice animations, and [thang010146]’s YouTube channel.
We hope to have piqued your curiosity in mechanical things. In these times of ultra fast developments in electronics, looking at the working of mechanisms that were developed centuries ago, but are still present and needed in our everyday lives can be a rewarding experience. We plan to work on more articles featuring interesting mechanisms so please let us know your favorites in the comments below.
Marble machines are the kind of useless mechanisms that everybody loves. Their sole purpose is to route marbles through different paths for your viewing pleasure. They can be extremely complicated contraptions, and sometimes that is the precisely the point. However, even a simple mechanism can be delightful to watch. [Denha] just uploaded his latest creation, using a spring as elevator and a simple zig-zag path.
The construction is relatively simple, a spring with the appropriate pitch for the steel balls size is used as an elevator. The spring is driven by a small electric motor via a couple of gears, and a wooden zig-zag path for the marbles lies next to the spring. The marbles go up with the spring and return in the wooden path in an endless journey.
We believe that a serious hacker should build a marble machine at least once in their life. We have posted several of them, from simple ones to other more complicated designs that require careful craftsmanship. [Denha]’s Youtube channel is full of good ideas to inspire your first project. In any case, watching a marble machine at work is quite a nice, relaxing experience.
[ossum] has a baby on the way. He admits that he got a bit carried away, brimming with parental excitement. What resulted is a fully articulated LED WiFi lamp that blooms and glows dramatically in the friendly confines of the oncoming baby’s room.
We’ve covered [ossum]’s work before. As usual, he started off by showing his complete mastery of Fusion360 and making the rest of us look bad. If you want to learn 360, we recommend scrobbing through his models to see how it’s done. The base encloses an ESP8266 and a hobby servo. A clever mechanism pulls down on a stranded steel cable that runs through the stem along with some control lines for the LEDS. This opens and closes the petals. The LEDs are all held in a 3D printed frame which produces a nice even glow.
Latvian artist [Krists Pudzens] just put on a show in Sweden and sent us the video of his amazing kinetic sculpture. (Embedded below.) We found an arty-theory writeup of another exhibition of his to share, but we had so many technical questions that we had to write him back asking for details. And boy, did he answer.
In the video, a couple of animatronic faces watch you as crab-like rope-climber bots inch upwards and red wings flap in the background. There’s a lot of brilliant mechanisms here, and aside from whatever it all means, we just like to watch machines go.
The details! Most of the pieces are plasma-cut steel or hand-cut-and-filed aluminum, and almost all of the motors are windshield wiper motors from old Russian KAMAZ and LADA cars. In another installation, the red wings (“Red Queens’ Race”) were installed in a public square and used to track the crowd, flapping faster as people moved more quickly by.
The robotic faces also use OpenCV to track you, and stare you down. One mask is vacuum-formed plastic, and the other is a copy in polyester resin and gelcoat. Here is a video of them on their own, and another of the development.
The twin rope-climbers, “Unbalanced Force”, just climb upwards at different paces. We were more than a little curious about what happens to the rope-climbers when they reach the top. [Krists] says the gallery staff grabs ladders and goes to fetch them. When he exhibited them in Poland on 20m ropes, they actually had to hire professional climbers. Life imitates art.
Some of us here at Hackaday are suckers for tech-art, whether it’s 3D-printed baroque columns, dancing with metal-bending machines, or just glowing globs of ferrofluid. There’s a lot of the same “wonder what would happen if…” tendency in the hacker and the artist — seeing possibilities and making them real.
It’s true that a lot of the projects we feature here (and build ourselves) are created to accomplish some sort of goal. But, many times the project itself is the goal. That’s the case with [Proto_G’s] self-oscillating pneumatic machine, which he built with no particular use in mind.