Tactical Build Makes Machining Splined Shaft A Snap

May 5, 2023 by Dan Maloney 9 Comments

Quick, what’s 360 divided by 23? It’s easy enough to get the answer, of course, but if you need to machine a feature every 15.652 degrees around a shaft, how exactly would you accomplish that? There are a number of ways, but they all involve some degree of machining wizardry. Or, you can just make the problem go away with a little automation.

The story behind [Tony Goacher]’s Rotary Table Buddy begins with some ATV tracks he got off AliExpress. His idea is to build a specialty electric vehicle for next year’s EMF Camp. The tracks require a splined shaft to drive them, which would need to be custom-made on a milling machine. A rotary table with a dividing plate — not as fancy as this one, of course –is usually the answer, but [Tony] was a little worried about getting everything set up correctly, so he embarked on a tactical automation solution to the problem.

An RP2040 provided the brains of the project, while a NEMA 23 stepper provides the brawn. [Tony] whipped up a quick PCB and 3D printed a case for the microcontroller, a stepper driver, an LCD display, and a few buttons. He 3D printed an adapter and a shaft coupler to mount the stepper motor to a rotary table. From there it was just a matter of coming up with a bit of code to run everything.

There’s a brief video in [Tony]’s blog post that shows Rotary Table Buddy in action, indexing to the next position after cutting one of the 23 splines. He says it took about ten minutes to cut each spline using this setup, which probably makes to total cutting time far less than the amount of time invested in the tool. But that’s hardly the point, and besides, now he’s set up for all kinds of machining operations in the future.

And we sure hope we hear about the EMF Camp build, too.

Jet Engine Tachometer Turned Into Unique CPU Utilization Meter

May 4, 2023 by Dan Maloney 16 Comments

When you’ve got a piece of interesting old aviation hardware on your desk, what do you do with it? If you’re not willing to relegate it to paperweight status, your only real choice is to tear it down to see what makes it tick. And if you’re lucky, you’ll be able to put it to work based on what you learned.

That’s what happened when [Glen Akins] came across a tachometer for a jet airplane, which he promptly turned into a unique CPU utilization gauge for his computer. Much of the write-up is concerned with probing the instrument’s innards to learn its secrets, although it was clear from the outset that his tachometer, from Kollsman Instruments, was electrically driven. [Glen]’s investigation revealed a 3-phase synchronous motor inside the tach. The motor drives a permanent magnet, which spins inside a copper cup attached to the needle on the tach’s face. Eddy currents induced in the cup by the spinning magnet create a torque that turns the needle against the force of a hairspring. Pretty simple — but how to put the instrument to work?

[Glen]’s solution was to build what amounts to a variable frequency drive (VFD). His power supply is based on techniques he used to explore aircraft synchros, which we covered a while back. The drive uses a trio of MCP4802 8-bit DACs to generate three phase-shifted sine waves via direct digital synthesis with an RP2040. The 3-phase signal drives the motor and spins the dial, with 84-Hz corresponding to full-scale deflection.

The video below shows the resulting CPU utilization gauge — which just queries for the current load level and sends it to the RP2040 over serial — in action. It’s not exactly responsive to rapid changes, but that’s to be expected from a mechanical system. And compared to exploring such a nice instrument, it really doesn’t matter.

Continue reading “Jet Engine Tachometer Turned Into Unique CPU Utilization Meter” →

Carbon Fiber And Kevlar Make This Linear Actuator Fast And Strong

May 3, 2023 by Dan Maloney 9 Comments

When it comes to the “build versus buy” question, “buy” almost always wins. The amount of time you have to put into building something is rarely justified, especially with a world of options available at the click of a mouse.

That’s not always the case, of course. These custom-made linear actuators are a perfect example of when building your own wins. For a planned ball-juggling robot, [Harrison Low] found himself in need of linear actuators with long throw distance, high speed, and stiff construction. Nothing commercially available checked all the boxes, so he set out to design his own.

A few design iterations later, [Harrison] arrived at the actuators you see in the video below. Built mainly from carbon fiber tubing and 3D-printed parts, the actuators have about 30 centimeters of throw, and thanks to their cable-drive design, they’re pretty fast — much faster than his earlier lead screw designs. The stiffness of the actuator comes by way of six bearings to guide the arm, arranged in two tiers of three, each offset by 60 degrees. Along with some clever eccentric spacers to fine-tune positioning, this design provides six points of contact that really lock the tube into place.

The cable drive system [Harrison] used is pretty neat too. A Kevlar kite string is attached to each end of the central tube and then through PTFE tubes to a pulley on an ODrive BLDC, which extends and retracts the actuator. It’s a clever design in that it keeps the weight of the motor away from the actuator, but it does have its problems, as [Harrison] admits. Still, the actuator works great, and it looks pretty cool while doing it. CAD and code are available if you want to roll your own.

These actuators are cool enough, but the real treat here will be the ball juggler [Harrison] is building. We’ve seen a few of those before, but this one looks like it’s going to be mighty impressive.

Continue reading “Carbon Fiber And Kevlar Make This Linear Actuator Fast And Strong” →

Exploring Woodworking Mysteries With Strain Gauges And Raspberry Pi

May 3, 2023 by Dan Maloney 19 Comments

If you’re not a woodworker, you might not have heard of the “45-degree rule.” It goes like this: a clamp exerts a force that radiates out across a triangular region of the wood that forms a right angle — 45 degrees on each side of the clamp’s point of contact. So, to ensure that force is applied as evenly as possible across the entire glue joint, clamps should be spaced so that these force triangles overlap. It’s a handy rule, especially for the woodworker looking to justify the purchase of more clamps; you can never have too many clamps. But is it valid?

The short answer that [ari kardasis] comes up with in the video below is… sort of. With the help of a wonderfully complex array of strain gauges and a Raspberry Pi, he found that the story isn’t so simple. Each strain gauge lives in a 3D printed bracket that spaces the sensors evenly along the wood under test, with a lot of work going into making the test setup as stiff as possible with steel reinforcement. There were some problems with a few strain gauges, but once he sorted that out, the test setup went into action.

[ari] tested clamping force transmission through pieces of wood of various widths, using both hardwoods and softwoods. In general, he found that the force pattern is much broader than the 45-degree rule suggests — he got over 60 degrees in some cases. Softwoods seemed to have a somewhat more acute pattern than hardwoods, but still greater than the rulebook says. At the end of the day, it seems like clamp spacing of two board widths will suffice for hardwoods, while 1.5 or so will do for softwoods. Either way, that means fewer clamps are needed.

A lot of woodworking is seat-of-the-pants stuff, so it’s nice to see a more rigorous analysis like this. It reminds us a lot of some of the experiments [Matthia Wandel] has done, like load testing various types of woods and glues.

Continue reading “Exploring Woodworking Mysteries With Strain Gauges And Raspberry Pi” →

Kerfmeter Measures Laser Cutter Kerf Allowances On The Fly

May 3, 2023 by Dan Maloney 21 Comments

Nothing beats a laser cutter and a sheet of Baltic birch plywood or MDF when it comes to making quick, attractive enclosures. Burning out all the pieces and fitting them together with finger joints is super satisfying — right up until you realize that you didn’t quite get the kerf allowance right, and your pieces don’t fit together very nicely. If only there was a way to automate kerf measurement.

There is, in the form of Kerfmeter. It comes to us by way of the lab of [Patrick Baudisch] at the University of Potsdam, where they’ve come up with a clever way to measure the kerf of a laser cutter right during the cutting session. With the Kerfmeter mounted directly to the laser cutter head, a small test artifact based on an Archimedean spiral is cut into a corner of the workpiece. Pins on a small motor engage with the object and turn it until it jams in its hole; the wider the kerf, the greater the angle. Once the kerf is calculated, the rest of the design can be dilated by the proper amount to achieve a perfect fit. The video below shows it better than words can explain it.

What we like about this is its simplicity — all it involves is a motor and a microcontroller, plus a little software. It seems much faster than using a traditional kerf gauge, not to mention more precise. And while it does use up a little bit of material, the test pattern is really pretty small, all things considered. Seems like a reasonable trade-off to us. Still, if you want to figure out your kerfs the old-fashioned way, we’ve got you covered.

Continue reading “Kerfmeter Measures Laser Cutter Kerf Allowances On The Fly” →

Getting Ready For Act 2 Of The Great American Eclipse

May 2, 2023 by Dan Maloney 41 Comments

It seems like only yesterday that the “Great American Eclipse” swept from coast to coast, and for those who were lucky enough to watch it from along the path of totality, it was a true life experience. No natural phenomenon can compete with the beauty of a total solar eclipse, and if there’s one thing I heard more than anything else in those golden moments after the Sun returned from behind the Moon, it was, “When’s the next one?” Everyone wanted to do it again, and for good reason.

Back in 2017, that question was kind of rhetorical; everyone knew the next eclipse to cross the United States was a mere seven years off. For me personally, the passage of time has not dampened my enthusiasm for eclipses one bit, and I suspect the feeling is mutual among the many people who gazed in wonder and childlike glee at the celestial proceedings of 2017. But except for the very lucky who live within the path of totality, mounting an expedition that optimizes the viewing experience takes preparation. Now that we’re a little less than a year away for the next one, it’s time to get geared up and make plans for the 2024 eclipse.

Where and When?

The 2017 eclipse’s “Great American Eclipse” moniker was well earned, as the continental United States was the sole beneficiary of the view. This time around, the US isn’t the only country along the path; Mexico and Canada will also get in on the fun. In fact, Mexico may well be the best place to watch the eclipse from, but more on that later. Continue reading “Getting Ready For Act 2 Of The Great American Eclipse” →

Machine Vision Automates Trainspotting With Unique Full-Length Portraits

May 2, 2023 by Dan Maloney 11 Comments

As hobbies go, trainspotting is just as valid a choice as any — we don’t judge. But it does present certain logistical challenges, such as having to be in visual range of a train to be able to spot it. There’s also the fact that trains are very large objects, and they tend to move very fast. What’s a railfan to do?

If you’re also technically minded, you might try building an automatic trainspotting bot like [jo-m] has. It looks like the hardware end of “Trainbot” is pretty simple since it has been tested on both x86 and Raspberry Pi, and supports both video4linux and Pi cam. The magic is in the software, which is able to detect a train entering the frame, record images, and then stitch them together into one long image. The whole thing is coded in Go and has some interesting bits, like a custom image patch mapping package.

Trainbot gives an unusual view of a train, one that most of us accustomed to watching a train pass at a crossing have never seen. By stitching small chunks of the train as it passes, Trainbot is able to show the entire train in a single image, which would be impossible to do except for being very, very far away from the track. [jo-m] also built a web interface for Trainbot where you can check out the comings and goings yourself. Each passing train’s image is accompanied by data like its velocity and acceleration, length of the train, and time of passage. There’s also a GIF of the original source video, which is pretty cool.

Here in the States, we don’t have a lot of passenger trains to spot, but we do have some really long freight trains. It’d be interesting to see how this works with a train that’s over a mile long; that would be quite an image. Looks like someone at least has the hardware in place to give it a try.