A helicopter blade uses a swash plate and a set of linkages to change the angle of the blades. Not only does it vary the collective pitch to increase or decrease thrust, but it varies each blade’s pitch throughout each rotation, letting it produce more lift on one side of the rotor. This presented a problem to [worked in theory] — he’s building an RC helicopter from scratch, and this mechanism added both complexity and weight. Instead, he started looking for a way to get around the problem.

There were two options to eliminate the linkages: a linkage-less swashplate design used in Black Hornet drones, and an under-actuated design using angled hinges to control the blade angle. [worked in theory] started with the Black Hornet design, which has the end of each blade run along the swashplate on wheels, while a central spring presses them down. Friction in the hinge and wheels proved too high, and it stopped responding at higher speeds. A second, lower-friction design seemed promising, but it still required actuators, and thus weight, to control the swashplate. [worked in theory] therefore moved on to the under-actuated approach. In this design, the blades are mounted on angled hinges — by varying the motor’s speed throughout each rotation, inertia causes the blades to swing backwards or forwards, changing their pitch.

[worked in theory] tested two such rotor designs: one with one hinge per rotor, and one with one hinge for both rotors. The design using a single hinge seemed less sensitive to friction, was more responsive in testing, and had a more linear control response, so he used that. To actually make the blades, [worked in theory] 3D printed them as flat blanks, then thermoformed them using printed molds. During testing, the blades needed weights added to pull them back toward the standard angle under constant rotation; fortunately, though, this had the side effect of damping out unwanted vibrations.

There’s still a long way to go before the helicopter’s finished, but this is quite an impressive start. This is the second under-actuated propeller we’ve seen recently, both inspired by [Tom Stanton]’s original design.

Anyone who’s ever built their own motors knows how tedious winding the coils soon becomes; in [Larry]’s case, the issue was even worse. He’s building his own flip-dot matrix display, and each dot uses two electromagnetic coils to flip a magnet in the dot. Rather than wind each of these by hand, therefore, he built his own coil-winding machine.

The coil winder uses two stepper motors: one to wind wire onto the bobbin, and one to move the wire guide carriage back and forth, distributing the wire evenly across the bobbin. The bobbin is held in place by a retainer, which doubles as a tie point for the end of the wire. The spool of wire rotates on a pair of bearings, and the wire is fed between two pieces of foam to provide adjustable tension. The housing is mostly 3D-printed, with some metal rods, bearings, and belt drives fleshing out the structure. On the electronics side, a Teensy controls the winder, with an OLED display and a rotary encoder for control. Before beginning on a coil, it homes the guide carriage against an end-stop switch, then winds on layers, keeping track of the number of layers applied.

We’ve seen a few coil winders here in the past, including a 3D printer adapted to winding stators. For more on this winder’s application, check out [Larry]’s flip-dot design.

As electronic components grow ever smaller, a microscope has become an increasingly indispensable tool for any fine work; when inspecting electronics, though, especially solder joints, [Corebb] found a top-down view too limiting, so he built his own microscope with a rotating side-angle view.

The microscope itself is made of a commercial C-mount microscope lens assembly and a USB camera; the lens has a variable magnification factor up to 200x, which is plenty for electronics work, and is mounted on an adjustable stand to move the focal point. This is paired with an LED ring for illumination and two polarizing filters, one mounted on the lens and one one the lighting ring; when adjusted to 90 degrees from each other, these eliminate glare from reflective surfaces.

To view subjects from the side, [Corebb] built a snap-on adapter. This uses a pair of mirrors to capture a view from the side of the object and direct this through the main microscope lens. An additional concave lens compensates for the increased length of the optical path, and ball bearings let the whole adapter rotate around the microscope and capture the subject from any angle. [Corebb] tried 3D-printing the adapter, but found that flexing caused too much jitter; in addition to being sturdier, a machined aluminium part reduced shadows by allowing for thinner supports. The adapter snaps onto the microscope with small magnets, which keep the optical path consistently aligned.

This isn’t the first time we’ve seen a soldering microscope with a view from the side, but this does look much more affordable. If you’d like to try the polarized light source with your microscope, we’ve covered that before.

Since the discovery of an undocumented I/Q sampling feature in ESP32 chips about two weeks ago, there’s been a flood of similar features being found in other wireless chips, including LoRa and Wi-Fi chipsets. The latest chip to join their ranks is the MediaTek MT7921AU, often used in Wi-Fi adapters, with two different projects developing independent SDR drivers for it in the last few days.

The first was BirriaSDR, which discovered that the chip exposes raw I/Q samples for debugging and calibration; BirriaSDR instead streams these to the host at 40 Msps in 14-bit resolution, with the option to tune from 2156 to 2610 MHz. BirriaSDR uses libusb to directly communicate with the Wi-Fi adapter and access its registers; it doesn’t make any permanent firmware changes, so the Wi-Fi adapter goes back to its original state after being used as an SDR. BirriaSDR implements an API similar to the RTL-SDR’s.

Mtk79ICAP, by contrast, exposes the MT7921AU’s sampling features over a standard SoapySDR interface. Unlike BirriaSDR, it applies some firmware changes to the chip, and it requires a modified driver to work. However, it can reach a maximum bandwidth of 80 MHz and tune to the 5 GHz bands. The Wi-Fi adapter in use can also simultaneously work in monitor mode and stream SDR data, though this only works when automatic gain control is enabled.

This is the second MediaTek chip we’ve seen repurposed for SDR work, after the earlier MT7996. Conveniently, Wi-Fi adapters often have external antennas, which should make it easier to connect a frequency mixer circuit. These adapters aren’t quite there yet, but some hackers have already used the ESP32 to transmit arbitrary signals.

Despite the recent leaps forward in other forms of computer-driven design, the reliability of PCB autorouters remains questionable; on the positive side, though, the lack of massive training data makes them plausible for a determined programmer to implement. For anyone contemplating this undertaking, [James Bowman] recommends a slightly unusual choice: use a hexagonal layout grid.

[James] built his own autorouter in his CuFlow PCB layout program. It takes a fairly straightforward approach: it represents the board as a grid of cells, and uses Lee’s algorithm to find the shortest routes between connected cells. The program initially used a square grid, but a hexagonal grid had a few advantages: in particular, each cell has six equidistant neighbors, rather than four (or eight, if you accept diagonal neighbors at a different distance), which allows denser routing. Because a hexagon more closely approximates a circle than a square, the same minimum-distance rules allow smaller cells, allowing the autorouter to pack more traces into the same space.

While we have previously seen a self-built autorouter, it’s much more common to interface with an external tool. If you start to get into high-speed PCB routing, though, building an autorouter becomes much harder.

Finding inexpensive broken hardware for sale, buying it, and restoring it to working condition is a long-standing tradition for hackers on a limited budge. But there are some devices that are so difficult to repair that it’s usually not worth the trouble. [Vintage560] is braver than most, though, and restored an internally-damaged Casio AW-330-AT altimeter watch.

The exterior of the watch was in good condition, other than missing a readily-replaced strap, but the battery had leaked into the interior, and the watch didn’t respond in any way to new batteries. Cleaning out the guts with isopropyl alcohol, repositioning a plastic insulator, and bending some contacts back into shape at least got some segments of the LCD display to activate, while over two days of turning the crown smoothed out resistance in the analog train.

Actually getting the LCD to work properly required disassembling the watch, taking particular care with the altitude sensor. It wasn’t clear what was wrong with the LCD — the controller seemed to be working properly, and several rounds of cleaning and adjusting the ZEBRA connector didn’t make any difference.

Eventually, [Vintage560] simply purchased a new screen. On close inspection, it looked as though chemicals from the leaking battery might have dissolved some of the transparent indium tin oxide contacts on the old display. With the watch now working [Vintage560] tested it on a trip to the Alps, and with a few periodic calibrations, it remained quite accurate.

Usually when we see Casio watch hacks, the watch in question is the F91W, whether it’s being used for contactless payments, being retrofitted as a smartwatch, or going 5,000 meters underwater.