Retrotechtacular: Synchros Go to War (and Peace)

Rotation. Motors rotate. Potentiometers and variable capacitors often rotate. It is a common task to have to rotate something remotely or measure the rotation of something. If I asked you today to rotate a volume control remotely, for example, you might offer up an open loop stepper motor or an RC-style servo. If you wanted to measure a rotation, you’d likely use some sort of optical or mechanical encoder. However, there’s a much older way to do those same tasks and one that still sees use in some equipment: a synchro.

The synchro dates back to the early 1900s when the Panama Canal used them to read and control valves and gates. These devices were very common in World War II equipment, too. In particular, they were often part of the mechanisms that set and read gun azimuth and elevation or — like the picture to the left — a position indication of a radar antenna. Even movie cameras used these devices for many years. Today, with more options, you don’t see them as much except in applications where their simplicity and ruggedness is necessary.

How Do They Work?

A synchro looks like a motor, but it is really a transformer optimized for specific applications. For example, it is common to see a synchro transmitter and a synchro receiver, although usually the devices can work as both. When wired together and excited with the proper AC voltage, turning one synchro shaft will turn the other the same amount. And one transmitter can drive multiple receivers. For example, an airplane cockpit may have an instrument that uses one transmitter and has two receivers, one for the pilot and another for the copilot.

A basic synchro is similar to a motor in that it has a rotor and a stator. However, each of these has a transformer winding. Some devices use single phase and others use three-phase. In addition, devices made for vehicles probably use 400 Hz AC instead of the 50 or 60 Hz common for stationary units. Usually, light-duty units made to drive indicators use single phase but synchros that transmit torque will use three-phase connections.

You can consider a synchro as a variable-coupling transformer. Rotating the shaft varies the magnitude of the magnetic coupling between the primary and secondary. That means the output voltage varies based on the shaft position. If you wire two synchros together, the circuit acts like a bridge. When the two devices are in the same position, the system is in balance — that is, putting out equal and opposing voltages. But if one shaft moves, the imbalance causes current to flow through the windings moving the other shaft to equilibrium. This configuration is sometimes known by the old General Electric name Selsyn. Other trade names included Teletorque and Autosyn, but you don’t hear those as often.

Variety and Power

There are many variations. Some synchros have brushes and others are brushless. Some are made for precision. In high precision applications, you may have a coarse transmitter slaved to a fine transmitter that rotates multiple times for each full rotation of the coarse shaft for reading a more precise value. You can think of this like a clock, where the big hand goes around twelve times for each rotation of the little hand. Usually, the gearing ratio is 36:1 or 72:1 so that each rotation of the fine shaft corresponds to five or ten degrees of the coarse transmitter.

Making a little handle turn a giant gun mount was problematic. At first, the receiver motor just told a human what to do using an indicator and then the human operated the gun. However, the development of the amplidyne made it possible to amplify the synchro outputs to directly drive larger loads.

The Amplidyne

The amplidyne has a superficial resemblance to a dynamotor — that is, a generator turned by a motor. However, in a dynamotor, you turn the generator to make a high voltage. In an amplidyne, the motor still turns the generator, but an input voltage is put on the generator’s field winding. The more current you apply, the higher the output voltage. This creates a very low-frequency amplifier that takes a current input and produces a voltage output.

Amplidynes found use in other applications, too. Elevators, locomotives, and even nuclear submarines. Of course, today, we have much better options for doing high power amplification, but there could be a few still hiding in some old building’s elevator, somewhere.

More Info

Because these were used extensively in the Navy, one of the best sources of information is an old Navy pamphlet (if you consider 166 pages a pamphlet; if it disappears, search for OP 1303). If you want something more modern, Moog (the aerospace company, not the synthesizer company, although the companies were founded by cousins) has an application guide and a handbook you might find interesting.

You won’t find too many of these interesting devices in use today, although there are companies that make modern encoders that specifically target traditional synchro applications. Of course, tubes made a comeback. Maybe that pile of World War II surplus synchros in the secret Hackaday bunker will be worth something one day.

Speaking of World War II, check out the 1944 instructional video below about airplanes that could move guns electrically using all these components.

Photo Credits:

Synchro by MGeek CC BY-SA-3.0

Posted in Hackaday Columns, hardware, position sensor, selsyn, synchro, world war II | Leave a comment

Friday Hack Chat: Control Schemes For Robotics

The Hackaday Prize is in full swing if you haven’t heard. It’s the Academy Awards of Open hardware, and the chance for you — yes, you — to create the next great piece of hardware and a better future for everyone. Right now, we’re in the Robotics Module Challenge portion of the prize. This is your chance to build a module that could be used in robotics projects across the world! Show off your mechatronic skills and build a robotics module that’s transferable to other builds!

Not coincidentally, for this week’s Hack Chat, we’re talking all about Robotics Modules. We’re taking a deep dive into actuation and control schemes for robotics, and you’re invited to take part. Everyone wants affordable robotics, and stepper and servo motors are no longer the domain of high-budget industrial robots. Everyone can build a robot, but how do you do that? That’s what we’re going to find out this Friday in the Hack Chat!

Our guest for this week’s Hack Chat is [Ryan Walker]. He holds a diploma in Mechatronics and Robotics from BCIT. He’s worked on everything from prosthetics to industrial automation, and his current hobbies include designing and building control algorithms that drive electronics and enable cheap hardware to excel! If you want to learn about robotics, this is the Hack Chat for you.

In this chat, we’ll be talking about:

  • Control schemes
  • How to actuate your projects
  • Wheels, tweels, and ways to make your project move
  • Automating robotics

You are, of course, encouraged to add your own questions to the discussion. You can do that by leaving a comment on the Hack Chat Event Page and we’ll put that in the queue for the Hack Chat discussion.join-hack-chat

Our Hack Chats are live community events on the Hack Chat group messaging. This week is just like any other, and we’ll be gathering ’round our video terminals at noon, Pacific, on Friday, April 27th.  Here’s a clock counting down the time until the Hack Chat starts.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on

You don’t have to wait until Friday; join whenever you want and you can see what the community is talking about.

Posted in 2018 Hackaday Prize, Hack Chat, Hackaday Columns, Hackaday Prize, robotics, robotics modules, The Hackaday Prize | Leave a comment

Reflow Rig Makes SMD Soldering a Wok in The Park

For a DIY reflow setup, most people seem to rely on the trusty thrift store toaster oven as a platform to hack. But there’s something to be said for heating the PCB directly rather than heating the surrounding air, and for that one can cruise the yard sales looking for a hot plate to convert. But an electric wok as a reflow hotplate? Sure, why not?

At the end of the day [ThomasVDD]’s reflow wok is the same as any other reflow build. It has a heat source that can be controlled easily, temperature sensors, and a microcontroller that can run the proportional-integral-derivative (PID) control algorithm needed for precise temperature control. That the heating element he used came from an electric wok was just a happy accident. A laser-cut MDF case complete with kerf-bent joints holds the heating element, the solid-state relay, and the Arduino Nano that runs the show. A MAX6675 thermocouple amp senses the temperature and allows the Nano to cycle the temperature through different profiles for different solders. It’s compact, simple, and [ThomasVDD] now has a spare wok to use on the stove top. What’s not to like?

Reflow doesn’t just mean oven or hotplate, of course. Why not give reflow headlights, a reflow blowtorch, or even a reflow work light a try?

Posted in arduino, control, hot plate, max 6675, pid, proportional-integral-derivative, reflow, smd, ssr, thermocouple, tool hacks | Leave a comment

Firing Bullets Through Propellers

Early airborne combat was more like a drive-by shooting as pilot used handheld firearms to fire upon other aircraft. Whomever could boost firepower and accuracy would have the upper hand and so machine guns were added to planes. But it certainly wasn’t as simple as just bolting one to the chassis.

This was during World War I which spanned 1914 to 1918 and the controllable airplane had been invented a mere eleven years before. Most airplanes still used wooden frames, fabric-covered wings, and external cable bracing. The engineers became pretty inventive, even finding ways to fire bullets through the path of the wooden propeller blades while somehow not tearing them to splinters.

Early Aerial Combat

AEG G.IV bomber with two gunner positions.AEG G.IV bomber with two gunner positions. Image source: CASM

At the start of the war, aerial combat involved pilots firing bullets at each other using handheld pistols or rifles and even throwing out rope to tangle the enemy’s propeller. The pistols were inaccurate and the rifles had a small chance of hitting a critical component. With the pilot both trying to fly the plane and fire a weapon at the same time, none of this was very effective.

It was when machine guns came into use in the latter part of 1914 that aerial combat really began. Some larger aircraft did carry dedicated gunners, such as the German AEG G.IV bomber pictured here but dedicated fighter craft carried just the pilot.

You may ask, why not mount forward-facing machine guns onto the wings? During World War I wings were braced using cables and didn’t provide as rigid a mounting position as the fuselage, resulting in vibrations which reduced accuracy. Also, with the guns so far away, the pilot couldn’t clear jams or reload. Though with later multi-crewed bombers, mechanics did often venture out onto the wings to perform maintenance.

Firing Over The Propeller

A Foster mount with a Lewis gun

For biplanes, the upper wing offered a location to mount a forward facing machine gun which would fire above the propeller. Being on the wing instead of the fuselage, it did lose accuracy due to vibration. But it allowed the pilot to both steer the plane and fire the gun at the same time. The British Foster mounting shown here was one such example.

The machine gun was mounted on a curved rail so that it could be pulled down by the pilot for clearing any jams and reloading. It could then be raised back up through a combination of springs and bungee cords.

Pilots found that they could also fire with the gun partway along the rail, such that it was pointing upward. This allowed them to shoot at the enemy from below and to the rear.

Deflecting Bullets Fired at the Propeller

Deflecting wedges mounted to a propeller

The most effective and preferred single-pilot fighter aircraft machine gun mounting was in front of the pilot on the fuselage where vibration was at a minimum. The pilot could steer the plane and aim the gun by the same action and could clear jams and reload. However, there was the small issue of having a propeller in the way. It would not do to cut away the ends of the wooden blades in mid-flight. Surprisingly, the first solution wasn’t really a solution at all but more of a hacked-together workaround.

One way to at least minimize propeller damage was to mount a steel wedge to the backside of the blades in line with where the bullets flew. Any bullets which hit it were deflected to one side. Shown here is a propeller with the wedges mounted at the correct radial distance from the center and with tiebars for bracing. This one was used by Roland Garros in April 1915 as a backup for the synchronization approach I talk more about below. While he scored several kills, he was forced to land due to engine failure, possibly caused by strain on the engine’s crankshaft by the bullets striking the deflectors.

But besides putting a strain on the engine, deflectors caused another problem. The propeller blades were typically made of laminated wood and the impacts, despite being deflected away by the steel deflectors, would cause the glue to weaken and the layers to separate. It was therefore preferable to avoid hitting the propeller.

Firing Through The Propeller: The Engine Literally Pulls the Trigger

Syncronization was the answer to avoid having bullets hit the propeller. One of the earliest mechanisms devised was the Fokker Stangensteuerung gear. It used a cam on the propeller shaft to push on a rod which pushed the gun’s trigger.

The cam was aligned to only fire when the path for the bullet was clear. Of course the gun shouldn’t fire every time the engine is turning, so there was a trigger lever which the pilot had to press to as a final part of the firing mechanism. The video below of a museum exhibit shows the mechanism in action but there are some subtleties which the following diagrams make clear.

How the Fokker Stangensteuerung synchronizer works

Enabling the cam follower: The system included an enabler mechanism that disconnects the cam follower to minimize wear. When it’s time for combat, the pilot pushed the trigger enabler forward, lowering the cam follower so that it can contact the cam. Note that at this point the pilot isn’t pressing the trigger lever and so the coupling piece remains pivoted up. As long as the coupling piece is pivoted upward, the push rod and coupling piece are prevented from pushing on the gun trigger.

Using the pilot trigger lever: When the pilot wished to fire the gun, he pushes on the trigger lever which pivots the coupling piece down. Note that depending on where the cam is in its rotation, the gun trigger may be in the way of the coupling piece pivoting down (as it is in the first diagram). But at some point in the cam’s rotation, the push rod will have pulled the coupling piece in the direction of the propeller far enough such that the coupling piece can pivot down. But the gun doesn’t fire yet.

Bullets begin to fire: The gun fires at only one point during the propeller’s rotation: when the bump on the cam is under the cam follower. When the bump pushes the cam follower up, the cam follower pushes the push rod toward the pilot, in turn pushing on the coupling piece which pushes on the gun trigger which fires a round in the gun. The cam’s alignment ensures the bullets pass between propeller blades.

The following video shows the synchronization gear of a German single-seat Fokker E-type monoplane. This is from an exhibit once on display in the Canada Aviation and Space Museum and simulates all the above actions as well as showing how things are restored to a non-combat stance after a battle.

Difficulties with Synchronization Propeller and Machine Gun

There were some difficulties with the synchronizers, as you’d expect of any mechanical system functioning at such a high rate of oscillation.

Temperature changes in the metal rods caused thermal expansion which resulted in their changing length. With such tight timing requirements, this would fire the bullet either sooner or later enough to hit a propeller blade.

Propeller speeds also varied during the flight. While you might think that it wouldn’t matter since the cam rotated at the same speed as the propeller, the firing of the gun took a length of time which was independent of the propeller speed. Even the distance the bullet had to travel was an issue with low muzzle-velocity guns and when the travel distance was sufficiently large. With some systems, the pilot had to keep an eye on the tachometer indicating the engine speed to know when it was safe to fire.

If all the above could be solved, many attempts to build synchronizers still failed due to the unreliable timing of many makes of gun. Even inaccuracies in bullet manufacturer meant that some bullets would fire at the wrong time, hitting a propeller blade.

Other Synchronizers

The pipes with drive shafts in the Zentralsteuerung systemThe pipes with drive shafts in the Zentralsteuerung system

Many synchronizer designs were developed during the war, some which introduced improvements. The German Fokker Zentralsteuerung gear did away with the cam and pushrods and instead connected a flexible drive shaft to the engine’s camshaft. This carried the rotation up to the gun itself.

Timing adjustments could now be done at the gun instead of at a single cam on a propeller shaft. This was especially useful when multiple guns were used in order to maximize the chances of hitting a critical part of the enemy plane. A separate flexible drive shaft was run up to each gun. Since each gun had slightly different timing, this meant that each could be adjusted individually. Also, should one gun fail, the others would still work.

Yet other means of synchronizing with the propeller position were electrical, using contacts around the propeller shaft to activate a solenoid at the gun trigger, and hydraulic. A modern implementation by a hacker would of course use a microcontroller and an airsoft gun.

The End Of Synchronizers

A number of things brought about the end of synchronizers. One was that the increased speed of aircraft made them harder to shoot down at the synchronizer’s firing rate. More powerful bombers used heavier armor for vital areas which rifle-caliber machine guns were unable to penetrate. The switch from cable-braced wings to the more rigid cantilever wings meant that guns could be mounted on the wings instead. And of course, the eventual introduction of jet engines meant there were no more propellers to fire through. The final synchronized guns were used during the Korean war in the early 1950s.

Posted in aerial, airplane, combat, Engineering, Fokker Zentralsteuerung, gear, history, machine gun, Original Art, propeller, synchronizer, weapons hacks, world war I, WWI | Leave a comment

Beat This Mario Block Like it Owes You Money

People trying to replicate their favorite items and gadgets from video games is nothing new, and with desktop 3D printing now at affordable prices, we’re seeing more of these types of projects than ever. At the risk of painting with too broad a stroke, most of these projects seem to revolve around weaponry; be it a mystic sword or a cobbled together plasma rifle, it seems most gamers want to hold the same piece of gear in the physical world that they do in the digital one.

But [Jonathan Whalen] walks a different path. When provided with the power to manifest physical objects, he decided to recreate the iconic “Question Block” from the Mario franchise. But not content to just have a big yellow cube sitting idly on his desk, he decided to make it functional. While you probably shouldn’t smash your head into the thing, if you give it a good knock it will launch gold coins into the air. Unfortunately you have to provide the gold coins yourself, at least until we get that whole alchemy thing figured out.

Printing the block itself is straightforward enough. It’s simply a 145 mm yellow cube, with indents on the side to accept the question mark printed in white and glued in. A neat enough piece of decoration perhaps, but not exactly a hack.

The real magic is on the inside. An Arduino Nano and a vibration sensor are used to detect when things start to get rough, which then sets the stepper motor into motion. Through an ingenious printed rack and pinion arrangement, a rubber band is pulled back and then released. When loaded with $1 US gold coins, all you need to do is jostle the cube around to cause a coin to shoot out of the top.

If this project has got you interested in the world of 3D printed props from the world of entertainment, don’t worry, we’ve got you covered.

Posted in 3d Printer hacks, 3d printing, arduino nano, mario, nintendo hacks, prop building, vibration sensor | Leave a comment

Émilie du Châtelet: An Energetic Life

Émilie du Châtelet lived a wild, wild life. She was a brilliant polymath who made important contributions to the Enlightenment, including adding a mathematical statement of conservation of energy into her French translation of Newton’s Principia, debunking the phlogiston theory of fire, and suggesting that what we would call infrared light carried heat.

She had good company; she was Voltaire’s lover and companion for fifteen years, and she built a private research institution out of a château with him before falling in love with a younger poet. She was tutored in math by Maupertuis and corresponded with Bernoulli and Euler. She was an avid gambler and handy with a sword. She died early, at 41 years, but those years that she did live were pretty amazing.

Portrait by Largillière. Pubic Domain via Wikimedia Commons

Daddy’s Little Girl

Émilie was born to a noble family in Paris in 1706. She was the youngest of six children, and the only girl. Her father made his living as a social assistant to Louis XIV. He doted on Émilie and did everything he could to nurse her astonishing intellect.

Each week, he invited brilliant scientists and writers into the family salon, and let Émilie sit in on these meetings of the minds and ask questions. With her father’s help, Émilie learned fencing and riding, studied math and science, and became fluent in several languages. When she’d exhausted the knowledge of her tutors, Émilie started educating herself.

The more intelligent she grew, the more horrified and furious her socialite mother became. She often threatened to send Émilie off to a convent, which was the normal route of education for French girls in the 1700s.

When Louis XIV died, her father lost his job and Émilie’s dowry began to suffer. Her mother sent her to live in the noble court at Versailles so she could find a husband before it was too late.

A Marriage of Convenience

At first, Émilie didn’t take the matter seriously. When she ran out of money to buy books, she used her math skills to win more by gambling. She also engaged in a public sword fight with a professional soldier that ended in a draw. Eventually she realized that her father wouldn’t be there forever. She needed to marry into a wealthy family or else would end up in a convent for life as an abandoned woman.

She started paying attention to the Marquis Florent-Claude du Châtelet. He was an army general and nearly twice her age, but Émilie’s father was certain that he would give her a good life, including the freedom to pursue her studies. Back then, it was not unusual for the upper classes to marry for status, then have affairs as they pleased.

Émilie and Voltaire on a picnic. Image via NPR

In Émilie’s estimation, her new husband was “a touch dull but decent–and unbothered by his brainy wife’s intellectual and amorous adventures.” Over the next five years, Émilie traveled with Florent-Claude wherever his military career took him, giving birth to two sons and a daughter along the way.

In 1730, she moved back to Paris to resume her studies and her social life. Soon after, she became friends with the philosopher and playwright Voltaire. Finally, she’d met her intellectual equal. They had an immediate chemistry and found much to say to each other on many subjects, from philosophy to science to political reform. She and Voltaire never made any attempt to hide their affair around Paris, which many found shameful.

Château de la Physique

Voltaire was known for being critical of the crown. He’d recently written Lettres philosophiques in which he rakes French politics and society over the coals. Around this time, he was advised by a friend that there was a warrant out for his arrest, and that he should hide.

Château du Cirey. Lithograph courtesy of Wikimedia Commons

Émilie and the Marquis invited him to escape to Château du Cirey, their mansion near the border of Champagne and Lorraine. The location was ideal for Voltaire, because he could go back and forth over the border when the heat was on. In exchange, Voltaire agreed to fund some much-needed château repairs.

Voltaire and Émilie had a great influence over each other. She eventually gave up her social life to join Voltaire at the remote château, and they evolved into the intellectual power couple of the Enlightenment. They turned the château into a sort of private research institution, inviting a number of the great minds of the time.

She began a deep study of algebra and calculus under the tutelage of Pierre-Louis Maupertuis, who introduced her to Isaac Newton’s ideas. Mulling over Newton led to her writing Institutes du Physique, which is regarded as her greatest philosophical contribution. In it, she explores and combines the ideas of many philosophers about religion, philosophy, and the natural world.

During this period, the dominant theory surrounding the nature of heat was that combustible substances contained something called phlogiston that is released during combustion and is responsible for what’s now called oxidation. Well, Émilie didn’t believe in the stuff. She and Voltaire set up a research laboratory in the château to study the nature and propagation of fire. Émilie’s research surfaced a few years later when she published a paper which gave great insight into the nature of light, suggesting that different colors of light had different energies, and hinting at the existence of what we now call infrared as the main carrier of heat.

Émilie and her trusty dividers. Via Wikipedia

Translating the Principia

Around 1740, Émilie began to translate Isaac Newton’s Principia into French. Her fluency in Latin combined with her intimate knowledge of Newton’s mathematical physics uniquely positioned her as one of the best people for the job.

But Émilie did more than just translate the work. She added notes, examples, and provided derivations that Newton glossed over. Along the way, she proposed that Newton’s conservation of momentum was mathematically generalizable into an overall conservation of energy, which she also demonstrated with Gravesande’s experiment: dropping balls onto sheets of clay, showing that the deformation was proportional to the square of the velocity. (Newton was fuzzy on the difference between momentum and energy, and would have said that the deformation depended on the momentum, being proportional to velocity.)

Émilie further claimed, in an additional chapter to the translation, that different types of energy — potential, kinetic, and heat — must be in the same units to be interchangeable. This was one piece in the big puzzle that would later become Lagrangian mechanics, and probably the most du Châtelet’s most important contribution to science, made in what would be the last year of her life.

Things had cooled romantically between her and Voltaire by the end of the decade. Émilie found a new lover, a young poet of the noble court. But he couldn’t keep up with her and her egg-headed friends, and turned cruel toward her. She became unintentionally pregnant by him at the age of 41, which was more or less a death sentence for a woman in the 1700s.

Émilie worked feverishly to finish translating the Principia before the baby came, fearing the worst. A few days after her daughter was born, Émilie died of a pulmonary embolism. Her husband, Voltaire, and the young poet were all at her side.

Posted in Biography, Émilie du Châtelet, Featured, fire, Isaac Newton, Original Art, philosophy, phlogiston, Principia, science, the Enlightenment, Voltaire | Leave a comment

Making 3D Objects The Scroll Saw Way

These days most have come to think that if you want to make a complex 3D object with all curved surfaces then a 3D printer is the only way to go. Many have even forgotten that once such things could be hand carved. [JEPLANS], on the other hand, is a master at making these objects using only a scroll saw as he’s done with his latest, a miniature camel cut from a single block of maple.

His process has a lot of similarities to 3D printing. He starts with a computer drawn design, in this case for the camel’s front and side. After cutting it out, he peels off the unwanted pieces and the camel emerges like magic from the block. But he didn’t like the amount of manual work he’d need in order to improve it further so he modifies the design by adding a top view, iterating just as you would with 3D printing. But after cutting that out, he finds he’d damaged one of the legs. And so he cuts out a new one but only after making one more design change, this time adjusting the camel’s head position. And with that result he’s satisfied. Check out his painstaking and somehow familiar process in the video below.

His isn’t the only masterful scroll saw work we’ve seen on Hackaday. Check out this beautiful acrylic skeleton clock with gears and linkages cut using a scroll saw.

Posted in classic hacks, scrollsaw, wood working | Leave a comment

A Buyer’s Guide to Lathe Options

Lathes are complicated machines, and buying one requires weighing a lot of options. We’ve already talked about buying new Asian, or old American machines (with apologies to the Germans, British, Swiss, and all the other fine 20th century machine tool making-countries). We also talked about bed length and swing, and you ain’t got nothin’ if you ain’t got that swing. Let’s talk about the feature set now. If you’re buying new, you’ll shop on these details. If you’re buying used, knowing the differences will help you pick a good project machine.

Imperial or Metric?

First and foremost — Imperial or metric? If you’re buying a new machine and you reside outside North America, the answer is, of course, metric. If you’re in North America, however, the choice is less clear. The gut instinct may be to go metric because it’s modern and “obviously better”, right? Well, not so fast. Most stock, hardware, and tools in North America are still more readily and cheaply found in Imperial sizes. You can go all metric, but you will be swimming against the current. That ivory tower has a lot of stairs, so think hard about how badly you want to sit in it.

Our most commented article of all time is a comparison of Imperial versus Metric. However, North American lathe buyers would do well to think carefully about this.

The next statement will shock and anger many of you, but here goes. For machine tool work, there is minimal practical difference between the two systems of measurement. Both have advantages and disadvantages. Before the Metric Squad spools up their decimal angry commenting machines, allow me to explain.

For dimensioning tasks in the typical range of machine parts (say, smaller than your hand), Imperial is easier. Thousandths are very convenient because everything is an integer, and common tolerances for press fits, hole clearances, etc, are all easily expressed and measured. With metric, you’re dealing in fractions of a millimeter, and there’s a lot of decimal points.

When working with hardware, such as drilling and tapping holes, choosing and measuring fasteners, and so forth, metric is definitely nicer. Metric drill sizes are easier to manage than the wacky Fraction-Letter-Number system that Imperial evolved into. The relationships between holes, threads, and fastener dimensions in metric are logical and easy to manage. With Imperial, you tape a chart to your wall and look at it a lot.

My personal recommendation is to be comfortable with both. Either machine can do both, though all tasks will be easier in the system the machine is designed for. Choose measuring tools that have both systems. Lots of the best books on machine shop theory and practice were written before metric existed, so be bilingual in your systems of measure.

Powering These Powerful Tools

Need a primer on 2-phase versus 3-phase? Here’s an article that talks about how we got to
where were are today
[Image Source: Split Phase Power by Charles Esson CC-BY 3.0]Okay, let’s talk power, now. The basic options you will encounter are household AC, three-phase AC, and DC. A household AC machine will typically use belts or gears to change the speed. You can make it more flexible by putting a big rheostat upstream of its power cord. Three-phase AC is typical of big industrial machines. You can replace the motor, or generate three-phase with a rotary converter (noisy and limited) or a Variable Frequency Drive (sexy). VFDs are the weapon of choice for one or two machines. If you have a whole shop full of big three-phase iron, a large rotary converter for the building makes more sense. However, VFDs are small, easy to use, and give you variable speed. They are complex and outside the scope of this article, but know that they exist.

For newer Asian machines, an exciting new option exists — brushless DC. These lathes get a lot of torque for their size. One horsepower for 10amps is typical, and that’s a lot of power for a small machine. You also get infinitely variable speed control for free, which is a huge advantage (especially when you’re first learning the dark art of feeds and speeds).

Choosing Power Feed Options

The author’s Precision Mathews PM-1022V, showing power feed clutch and half-nut controls. The carriage is keyway-driven, as shown.

The next thing to think about is power feed. Most lathes have it, but it comes in many forms. Power feeding is valuable because it yields better surface finishes, and takes much of the tedium out of long operations. It’s also how single-point thread cutting is done — the drivetrain is synchronized to generate the right helix for the thread you need.

Delicious thread-cutting close-up by Rolf R Bakke on YouTube

Almost all machines will have a half-nut that clamps to the lead screw for cutting threads. The cheapest machines will also rely on this for power feed. The next level up in quality will have a separate clutch (in addition to the half-nut) for driving the carriage. This is typically done with a keyway that runs the length of the lead screw. A keyed gear in the carriage taps power off this, without engaging with the threads of the lead screw. This is a nice compromise because you don’t wear out the leadscrew threads, but the machine remains inexpensive. Larger and higher-end machines will have a dedicated driveshaft running parallel to the lead screw to drive the carriage. You may see multiple shafts running parallel, some for power transmission, some for various control functions. It gets crazy up there in the clouds with the likes of Monarch and Lodge & Shipley.

Benchtop machines typically only have longitudinal power feed (the carriage, or “X-axis” if you like). Some higher end bench top machines are now starting to offer power cross-feed as well, and this is a very nice feature if you’ll be facing larger diameter pieces. It also helps get smooth parting operations. Larger machines will have power cross-feed de rigeur.

The final element of power feed is the driving of the lead screw. This can be done with change gears, a transmission, or some combination thereof. Low end machines will have only change-gears, which means you need to physically swap out gear sets for every change of feed-speed that you want. This is the road to hell. Look for a quick-change gearbox with three or more speed options. Some also have a reverse feed option, which is a nice touch, because you can cut left-hand threads. Higher-end machines will have transmissions as complex as a tractor, with all manner of speed and direction options. These are great to use, but be wary of complex gear boxes if you’re doing a restoration project. It’s easy to underestimate the complexity of the drivetrain in these beasts, and many are filled with unobtainium parts that were abused by some gear-jamming rig jockey of years past.

Tool Posts

Now let’s talk tool posts. These days, lower end machines will have a four-way tool post, which holds one cutting tool, and three things to slash your hand open when you brush past them. Tool height is set with shims and a lot of swearing.

For a little more money, you can generally get a Quick Change Tool Post. On these, tool height is set with a thumbscrew on the tool holder, and the setting is permanently “saved” with each tool. QCTPs are all pretty much based on the Aloris design of years past. Cheaper ones will have a piston lock, slightly better ones will have a tapered wedge lock. Both are fine. Let’s be clear on this point: get a quick change tool post. It will change your life (and get you addicted to tool holders). Just make sure it’s a standard size, like AXA or BXA. Otherwise you’ll spend a fortune on tool holders, and trust me, you never have enough tool holders. I throw a couple on the invoice with every order I place at suppliers like MSC Direct or LittleMachineShop, and it’s still never enough.

Really old machines will have “lantern” tool posts, which use a curved wedge to set tool height and angle. Purists like these for the old-timey aesthetic, but they aren’t very rigid and you had best not be in a hurry when setting one up.

Chucks, Rests, and Other Accessories

The last major thing to look for is what accessories the machine comes with. If you only get one chuck, make it an independent four-jaw. It’s easily the most versatile. Three-jaw scroll chucks are a convenience (and they are turbo convenient) but you will need an independent four-jaw for true precision work. You also want a faceplate for all the odd-shaped things. Exotic options include a collet chuck, 4-jaw scroll chuck, and six-jaw chucks. These are very expensive new, but older project machines often come with great stuff like this. Buy all these extra chucks new if you are made of money or because you hate me and want to send me photos of nice things I can’t have.

Also worth noting are the rests. Any machine should come with a steady-rest, which is used to support the end of a long piece when the tailstock would be in the way. Less commonly used is the follow-rest, which rides on the carriage and applies counter-pressure to the back side of where the tool is cutting. This is useful for working on long thin pieces, where the work would deflect under cutting pressure. New machines will come with both rests, but old used machines may not. These can be hard to find for a vintage machine after the fact, so try to make sure you get a steady-rest, at least.

Weigh These Options Carefully

If you’re shopping for a lathe (and you should be) you’ll quickly find that every machine differs along one of these vectors. There are a lot of choices, even within the same brand and size range, so research carefully. When buying new, I recommend downloading the manuals for the machines to see exactly what features they have. When buying used, learn to scrutinize grainy flip-phone photos on craigslist for desirable details like a separate drive shaft for the carriage or a dusty old collet chuck sitting in the back. Like buying a car, buying a machine tool is an exercise is cross-referencing the features you want with the features you can afford, to find your own sweet spot.

Happy lathe shopping! Next time we’ll talk about getting ready to receive your new machine, and setting up its new home in your shop.

Posted in buyer's guide, Engineering, Featured, lathe, machine tools, options, power feed, tool post | Leave a comment

Heat Seeking Robot and Camera Tear Down

[Marco Reps] found an HT02 thermal imaging camera in his mailbox. He found the resolution was fine for looking at big objects but worthless for examining circuit boards. So he decided to just tear it into pieces — an urge we totally understand.

Inside was a thermopile sensor that was easy to reverse engineer. So [Marco] decided to rework a Raspberry Pi robot to use the camera and turn it into a heat seeker.

The camera is relatively inexpensive compared to other similar devices and apparently uses a cheaper sensor type. However, the sensor itself was easy to use. [Marco] found a pin that is pulsed every half second to trigger acquisition. Another pin produces a few thousand pulses which is your cue to read an analog output from the device. It is really that simple.

For the right application, the HT02 might be worth the low price, although we’ve heard stories that they are not always constructed well. One feature we thought was interesting was the ability to merge a visible light image with the infrared image merged so you can get a better idea of what you are looking at.

The low cost and low resolution reminded us of an entry in the Hackaday prize a few years ago. Then again, you can take a more minimal approach and build up a scanner that works point by point.

Posted in digital cameras hacks, robot, robots hacks, thermal imaging, thermopile | Leave a comment

Dissecting the AVR debugWire

Anyone who’s ever written more than a dozen or so lines of code knows that debugging is a part of life in our world. Anyone who’s written code for microcontrollers knows that physical debugging is a part of our life as well. Atmel processors use a serial communications protocol called debugWire, which is a simpler version of JTAG and allows full read/write access to all registers and allows one to single step, break, etc. [Nerd Ralph], a prominent fixture here at Hackaday has dug into the AVR debugWire protocol and enlightened us with some valuable information.

While the protocol side of debugWire is a mostly-solved problem, the physical layer was giving him trouble. He started with a diode, and then went through a couple resistors and other components to interface with the debugWire pin on the AVR microcontroller, doing most of the troubleshooting work so now you don’t have to. He notes that interface components might need to be tailored to specific USB-TTL adapters, so keep that in mind if you care to delve into working with debugWire yourself.

We’re no strangers to debugging techniques here at Hackaday. As always, be sure to let us know if you run across any new techniques or try anything new yourself!

Posted in AVR, debug, debugwire, Microcontrollers | Leave a comment