Today, if you want to teach kids the art of counting to one, you’re going to drag out a computer or an iPad. Install Scratch. Break out an Arduino, or something. This is high technology to solve the simple problem of teaching ANDs and ORs, counting to 0x0F, and very basic algorithms.
At the Vintage Computer Festival East this year, System Source, proprietors of a fantastic museum of not-quite-computing equipment brought out a few of their best exhibits. These include mechanical calculators, toys from the 60s, and analog computers that are today more at home in a CS departments’ storage closet than a classroom. It’s fantastic stuff, and shows exactly how much you can learn with some very cleverly designed mechanical hardware.
The Vintage Computer Festival East is going down right now, and I’m surrounded by the height of technology from the 1970s and 80s. Oddly enough, Hackaday frequently covers another technology from the 80s, although you wouldn’t think of it as such. 3D printing was invented in the late 1980s, and since patents are only around for 20 years, this means 3D printing first became popular back in the 2000’s.
In the 1970s, the first personal computers came out of garages. In the early 2000s, the first 3D printers came out of workshops and hackerspaces. These parallels pose an interesting question – is it possible to build a 1980s-era 3D printer controlled by a contemporary computer? That was the focus of a talk from [Ethan Dicks] of the Columbus Idea Foundry this weekend at the Vintage Computer Festival.
Pong may not be much anymore, but it’s the granddaddy of all video games, and there’s still a lot to learn by studying its guts. And what better way to do that than by having it all laid out before you as you play? All it takes is 200 discrete transistors and two large handfuls of passives tacked to a piece of copper clad board to get a version of Pong executed without a single chip that’s playable on an oscilloscope.
Clearly a labor of love, if not an act of temporary insanity, [GK]’s realization of Pong is a sight to behold. Every scrap of it is circuits of his own design, executed dead bug style, apparently because [GK] enjoys life on hard mode. The game itself is surprisingly playable and you can even play against the machine. The video below is a little hard to watch, what with some glare on the oscilloscope CRT, but we’ll cut [GK] plenty of slack on this one; after all, it looks like this whole project was pulled off in one marathon weekend build session.
We’re still busy poring over the hand-drawn Forrest Mims-style schematics, which by themselves are almost a complete course in analog design. A lot of the circuits remind us [GK]’s bouncing ball simulation, which we covered a while back.
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
Deployable mirror with scissor linkages. By [Catsquisher] via Wikimedia CommonsThe 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.
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.
An example from nature, the Moray eel. Image from [Matthew West]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.
[Jack Eisenmann] is no stranger to building impressive DIY CPU’s on vast stretches of breadboard. This time [Jack] has done away with the seventeen breadboards he used in his last 8-bit computer and instead has gone a step further and designed a set of generously utilised PCB’s for the CPU. The result is the DUO Enterprise.
The CPU design is based around an 8-bit data bus and a 24-bit address bus. As usual, a minimal yet carefully chosen instruction set allows [Jack] to do all the heavy lifting in software as part of the compiler and operating system he is working on. There is no sign of a display yet, instead the computer communicates via a dumb terminal. We love the aluminum foil for shielding! Check out the video, below, to see what we mean.
His final goal with DUO Enterprise is to allow anyone to utilise its computing power by submitting programs and calculations. Heads up [Jack], our neural net needs training soon.
In the comments to our recent article about Wimshurst machines, we saw that some hackers had never heard of them, reminding us that we all have different backgrounds and much to share. Well here’s one I’m guessing even fewer will have heard of. It’s never even shown up in a single Hackaday article, something that was also pointed out in a comment to that Wimshurst article. It is the Lord Kelvin’s Water Dropper aka Lord Kelvin’s Thunderstorm, invented in the 1860s by William Thomson, 1st Baron Kelvin, the same fellow for whom the Kelvin temperature scale is named. It’s a device that produces a high voltage and sparks from falling drops of water.
Hands up if you’ve ever used a machine running CP/M. That’s likely these days to only produce an answer from owners of retrocomputers. What was once one of the premier microcomputer operating systems is now an esoteric OS, a piece of abandonware released as open source by the successor company of its developer.
In the 1970s you’d have seen CP/M on a high-end office wordprocessor, and in the 1980s some of the better-specified home computers could run it. And now? Aside from those retrocomputers, how about running CP/M on an ESP8266? From multi-thousand-dollar business system to two-dollar module in four decades, that’s technological progress.
[Matseng] has CP/M 2.2 running in a Z80 emulator on an ESP8266. It gives CP/M 64K of RAM, a generous collection of fifteen 250K floppy drives, and a serial port for communication. Unfortunately it doesn’t have space for the ESP’s party piece: wireless networking, but he’s working on that one too. If you don’t mind only 36K of RAM and one less floppy, that is. All the code can be found on a GitHub repository, so if you fancy a 1970s business desktop computer the size of a postage stamp, you can have a go too.
There’s something gloriously barmy about running a 1970s OS on a two-dollar microcontroller, but if you have to ask why then maybe you just don’t understand. You don’t have to have an ESP8266 though, if you want you can run a bare-metal CP/M on a Raspberry Pi.
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.
