Testing At Scale

January 28, 2025 by Al Williams 15 Comments

We’ve said it before: building one-offs is different from building at scale. Even on a small scale. There was a time when it was rare for a hobbyist to produce more than one of anything, but these days, access to cheap PC boards makes small production runs much more common. [VoltLog], for example, is selling some modules and found he was spending a lot of time testing the boards. The answer? A testing jig for his PC board.

Big factories, of course, have special machines for bulk testing. These are usually expensive. [VoltLog] found a place specializing in creating custom test jigs using 3D printing.

They also have some standard machines. He did have to modify his PCB to accommodate special test points. He sent the design files to the company, and they produced a semi-custom testing jig for the boards in about a month.

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Laser-Cut Metal Endoskeleton Beefs Up 3D Prints

January 24, 2025 by Dan Maloney 23 Comments

There are limits to what you can do with an FDM printer to make your parts stronger. It really comes down to adding more plastic, like increasing wall thickness or boosting up the infill percentage. Other than that, redesigning the part to put more material where the part is most likely to fail is about the only other thing you can do. Unless, of course, you have access to a fiber laser cutter that can make internal metal supports for your prints.

As [Paul] explains it, this project stemmed from an unfortunate episode where a printed monitor stand failed, sending the LCD panel to its doom. He had taken care to reinforce that part by filling it with fiberglass resin, but to no avail. Unwilling to risk a repeat with a new tablet holder, he decided to test several alternative methods for reinforcing parts. Using a 100 W fiber laser cutter, he cut different internal supports from 0.2 mm steel shim stock. In one case he simply sandwiched the support between two half-thickness brackets, while in another he embedded the steel right into the print. He also made two parts that were filled with epoxy resin, one with a steel support embedded and one without.

The test setup was very simple, just a crane scale to measure the force exerted by pulling down on the part with his foot; crude, but effective. Every reinforced part performed better than a plain printed part with no reinforcement, but the clear winner was the epoxy-filled part with a solid-metal insert. Honestly, we were surprised at how much benefit such a thin piece of metal offered, even when it was directly embedded into the print during a pause.

Not everyone has access to a fiber laser cutter, of course, so this method might not be for everyone. In that case, you might want to check out other ways to beef up your prints, including just splitting them in two.

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AA Battery Performances Tested, So Get The Most For Your Money

January 10, 2025 by Donald Papp 38 Comments

[Project Farm] has a video in which a wide variety of AA cells are analyzed and compared in terms of capacity, internal resistance, ability to deliver voltage under load, and ability to perform in sub-freezing temperatures. Alkaline, lithium, and even some mature rechargeable cells with a couple thousand cycles under their belt were all compared. There are a few interesting results that will can help you get the most from your money the next time you’re battery shopping.

The video embedded below demonstrates a set of tests that we recommend you check out, but the short version is that more expensive (non-rechargeable) lithium cells outperform their alkaline peers, especially when it comes to overall longevity, ability to perform under high-drain conditions, and low temperatures. Lithium cells also cost more, but they’re the right choice for some applications.

Some brands performed better and others worse, but outside of a couple stinkers most were more or less comparable. Price however, was not.

As for how different brands stack up against one another, many of them are more or less in the same ballpark when it comes to performance. Certainly there are better and worse performers, but outside of a couple of stinkers the rest measure up reasonably well. Another interesting finding was that among rechargeable cells that were all several years (and roughly 2,200 charge-discharge cycles) old, a good number of them still performed like new.

Probably the single most striking difference among the different cells is cost — and we’re not just talking about whether lithium versus alkaline AAs are more cost-effective in the long run. Some brands simply cost twice as much (or more!) than others with comparable performance. If you’re in a hurry, jump to [Project Farm] presenting the final ranked results at 19:45 in.

Relying on brand recognition may save you from buying complete junk, but it’s clearly not the most cost-effective way to go about buying batteries. These findings are similar to an earlier effort at wide-scale battery testing which also determined that factoring in price-per-cell was too significant to ignore.

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Making Sure Your Patch Cables Are Ready For RF Work

January 8, 2025 by Dan Maloney 3 Comments

How do you know that your patch cables are good? For simple jumper wires, a multimeter is about all you need to know for sure. But things can get weird in the RF world, in which case you might want to keep these coaxial patch cable testing tips in mind.

Of course, no matter how high the frequency, the basics still apply, and [FesZ] points out in the video below that you can still get a lot of mileage out of the Mark 1 eyeball and a simple DMM. Visual inspection of the cable and terminations can reveal a lot, as can continuity measurements on both the inner and outer conductors. Checking for shorts between conductors is important, too. But just because the cable reads good at DC doesn’t mean that problems aren’t still lurking. That’s when [FesZ] recommends breaking out a vector network analyzer like the NanoVNA. This tool will allow you to measure the cable’s attenuation and return loss parameters across the frequency range over which the cable will be used.

For stubborn problems, or just for funsies, there’s also time-domain reflectometry, which can be done with a pulse generator and an oscilloscope to characterize impedance discontinuities in the cable. We’ve covered simple TDR measurement techniques before, but [FesZ] showed a neat trick called time-domain transformation, which uses VNA data to visualize the impedance profile of the whole cable assembly, including its terminations.

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Torque Testing 3D Printed Screws

December 3, 2024 by Dan Maloney 18 Comments

Unless you’ve got a shop with a well-stocked hardware bin, it’s a trip to the hardware store when you need a special screw. But [Sanford Prime] has a different approach: he prints his hardware, at least for non-critical applications. Just how much abuse these plastic screws can withstand was an open question, though, until he did a little torque testing to find out.

To run the experiments, [Sanford]’s first stop was Harbor Freight, where he procured their cheapest digital torque adapter. The test fixture was similarly expedient — just a piece of wood with a hole drilled in it and a wrench holding a nut. The screws were FDM printed in PLA, ten in total, each identical in diameter, length, and thread pitch, but with differing wall thicknesses and gyroid infill percentages. Each was threaded into the captive nut and torqued with a 3/8″ ratchet wrench, with indicated torque at fastener failure recorded.

Perhaps unsurprisingly, overall strength was pretty low, amounting to only 11 inch-pounds (1.24 Nm) at the low end. The thicker the walls and the greater the infill percentage, the stronger the screws tended to be. The failures were almost universally in the threaded part of the fastener, with the exception being at the junction between the head and the shank of one screw. Since the screws were all printed vertically with their heads down on the print bed, all the failures were along the plane of printing. This prompted a separate test with a screw printed horizontally, which survived to a relatively whopping 145 in-lb, which is twice what the best of the other test group could manage.

[Sanford Prime] is careful to note that this is a rough experiment, and the results need to be taken with a large pinch of salt. There are plenty of sources of variability, not least of which is the fact that most of the measured torques were below the specified lower calibrated range for the torque tester used. Still, it’s a useful demonstration of the capabilities of 3D-printed threaded fasteners, and their limitations.

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Studying The Finer Points Of 3D Printed Gears

June 12, 2024 by Dave Rowntree 34 Comments

[How to Mechatronics] on YouTube endeavored to create a comprehensive guide comparing the various factors that affect the performance of 3D printed gears. Given the numerous variables involved, this is a challenging task, but it aims to shed light on the differences. The guide focuses on three types of gears: the spur gear with straight teeth parallel to the gear axis, the helical gear with teeth at an angle, and the herringbone gear, which combines two helical gear designs. Furthermore, the guide delves into how printing factors such as infill density impact strength, and it tests various materials, including PLA, carbon fiber PLA, ABS, PETG, ASA, and nylon, to determine the best options.

The spur gear is highly efficient due to the minimal contact path when the gears are engaged. However, the sudden contact mechanism, as the teeth engage, creates a high impulse load, which can negatively affect durability and increase noise. On the other hand, helical gears have a more gradual engagement, resulting in reduced noise and smoother operation. This leads to an increased load-carrying capacity, thus improving durability and lifespan.

It’s worth noting that multiple teeth are involved in power transmission, with the gradual engagement and disengagement of the tooth being spread out over more teeth than the spur design. The downside is that there is a significant sideways force due to the inclined angle of the teeth, which must be considered in the enclosing structure and may require an additional bearing surface to handle it. Herringbone gears solve this problem by using two helical gears thrusting in opposite directions, cancelling out the force.

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Do You Trust Your Cheap Fuses?

April 11, 2024 by Jenny List 34 Comments

When a fuse is fitted in a power rail, it gives the peace of mind that the circuit is protected. But in the case of some cheap unbranded fuses of the type that come in kits from the usual online suppliers that trust can be illusory, as they fail to meet the required specification.

[Andreas Spiess] has used just these fuses for protection for years as no doubt have many of you, so it was something of a shock for him to discover that sometimes they don’t make the grade. He’s taken a look at the issue for himself, and come up with an accessible way to test your fuses if you have any of those cheap ones.

It’s an interesting journey into the way fuses work, as we’re reminded that the value written on the fuse isn’t the current at which it blows but the maximum it’s intended to take. The specification for fuses should have a graph showing how quickly one should blow at what currents above that level, and the worry was that this time would be simply too long for the cheap ones.

In the video below the break, he looks at the various set-ups required to test a fuse, and instead of a bank of large power supplies, he came up with a circuit involving an 18650 cell and three one ohm resistors in parallel. The resulting 1/3 ohm resistor should pass in the region of 10 A when connected across the 18650, so with a 5 A fuse in that circuit and a storage ‘scope he’s able to quickly test a few candidates. He found that the cheap fuses he had were slower to blow than a Bosch part but weren’t as worrisome as he’d at first thought. If you have any of these parts, maybe you should take a look at them too?

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