[Joe Barnard] made a solid propellant rocket motor, and as one does in such situations, he put it through its paces on the test stand. The video below is not about the test, nor is it about the motor’s construction. Rather, it’s a deconstruction of the remains of the motor in order to better understand its design, and it’s pretty interesting stuff.

Somewhere along the way, [Joe], aka “BPS.Space” on YouTube, transitioned from enthusiastic model rocketeer to full-fledged missile-man, and in the process stepped up his motor game considerably. The motor that goes under the knife — or rather, the bandsaw — in this video is his “Simplex V2,” a completely DIY build of [Joe]’s design. For scale, the casing is made from a 6″ (15 cm) diameter piece of aluminum tubing over a meter in length, with a machined aluminum forward closure and a composite nozzle assembly. This is a pretty serious piece of engineering.

The closure and the nozzle are the focus of the video, which makes sense since that’s where most of the action takes place. To understand what happened during the test, [Joe] lopped them off and cut them roughly in half longitudinally. The nozzle throat, which was machined from a slug of graphite, fared remarkably well during the test, accumulating only a little slag from the propellant, a combination of powdered aluminum, ammonium perchlorate, and HTBP resin. The lower part of the nozzle, made from phenolic-impregnated linen, did pretty well too, building up a pyrolyzed layer that acted much like a space capsule’s ablative heat shield would. The forward closure, whose sole job is to contain the inferno and direct the exhaust anywhere but up, took more of a beating but stood up to the challenge. Especially interesting was the state of the O-rings and the way that the igniter interfaced with the closure.

Post mortems like these are valuable teaching tools, and while it must be heartbreaking to destroy something you put so much work into, you can’t improve what you can’t measure. Hats off to [Joe] for the peek inside his world.

Kitting out a full workshop can be expensive, but if you’re only working on small things, it can also be overkill. Indeed, if your machining tends towards the miniature, consider building yourself a series of tiny machines like [KendinYap] did. In the video below, you can see the miniature electric sander, table saw, drill press, and cut-off saw put through their paces.

Just because the machines are small, doesn’t mean they’re not useful. In fact, they’re kind of great for doing smaller jobs without destroying what you’re working on. The tiny belt sander in particular appeals in this case, but the same applies to the drill press as well. [KendinYap] also shows off a tiny table and circular saw. The machines are straightforward in their design, relying largely on 3D printed components. They’re all powered by basic DC brushed motors which are enough to get the job done on the small scale.

They look particularly good if tiny scale model-making is your passion.

Benchy is that cute little boat that everyone uses to calibrate their 3D printer. [Emily The Engineer] asked the obvious question—why isn’t it a real working boat? Then she followed through on the execution. Bravo, [Emily]. Bravo.

The full concept is straightforward, but that doesn’t make it any less fun. [Emily] starts by trying to get small Benchys to float, and then steadily steps up the size, solving problems along the way. By the end of it, the big Benchy is printed out of lots of smaller sections that were then assembled into a larger whole. This was achieved with glue and simply using a soldering iron to melt parts together. It’s a common technique used to build giant parts on smaller 3D printers, and it works pretty well.

The basic hull did okay at first, save for some stability problems. Amazingly, though, it was remarkably well sealed against water ingress. It then got a trolling motor, survived a capsizing, and eventually took to the open water with the aid of some additional floatation.

We’ve seen big Benchys before, and we’ve seen fully functional 3D-printed boats before, too. It was about time the two concepts met in reality. Video after the break.

We don’t know how you feel when designing hardware, but we get uncomfortable at the extremes. High voltage or current, low noise figures, or extreme frequencies make us nervous.  [Orion Serup] from CrabLabs has been turning up a few of those variables and has created a fairly beefy 3-phase motor driver using GaN technology that can operate up to 80V at 70A. GaN semiconductors are a newer technology that enables greater power handling in smaller packages than seems possible, thanks to high electron mobility and thermal conductivity in the material compared to silicon.

The KiCAD schematic shows a typical high-power driver configuration, broken down into a gate pre-driver, the driver itself, and the following current and voltage sense sub-circuits. As is typical with high-power drivers, these operate in a half-bridge configuration with identical N-channel GaN transistors (specifically part EPC2361) driven by dedicated gate drivers (that’s the pre-driver bit) to feed enough current into the device to enable it to switch quickly and reliably.

The design uses the LM1025 low-side driver chip for this task, as you’d be hard-pushed to drive a GaN transistor with discrete components! You may be surprised that the half-bridge driver uses a pair of N-channel devices, not a symmetric P and N arrangement, as you might use to drive a low-power DC motor. This is simply because, at these power levels, P-channel devices are a rarity.

Why are P-channel devices rare? N-channel devices utilise electrons as the majority charge carrier, but P-channel devices utilise holes, and the mobility of holes in GaN is very low compared to that of electrons, resulting in much worse ON-resistance in a P-channel and, as a consequence, limited performance. That’s why you rarely see P-channel devices in a circuit like this.

Of course, schematic details are only part of the problem. High-power design at the PCB level also requires careful consideration. As seen from the project images, this involves heavy, thick copper traces on two or more heavily via-stitched layers to maximise copper volume and lower resistance as far as possible.  But, you can overdo this and end up with too much inductance in critical areas, quickly killing many high-power devices. Another vital area is the footprint design for the GaN device and how it connects to the rest of the circuit. Get this wrong or mess up the soldering, and you can quickly end up with a much worse performance!

We’ve seen DIY high-power controllers here a few times. Here’s an EV controller that uses discrete power modules. Another design we saw a few years ago drives IGBTs for a power output of 90kW.