3D Printed Mini Drone Test Gimbal

Drones are a pain, especially mini ones. When you are designing, building (or even reviewing) them, they inevitably fly off in some random direction, inevitably towards your long-suffering dog, hit him in the butt and send him scuttling off in search of a quieter spot for a nap.

[Tristan Dijkstra] and [Suryansh Sharma] have a solution: a mini-drone test gimbal. The two are in the the Networked Systems group and the Biomorphic Intelligence Lab who use CrazyFlie drones in their work, which require regular calibration and testing. This excellent design allows the drone to rotate in three dimensions, while still remaining safely contained. That means I could test the flight characteristics of a drone without endangering my dogs important napping schedule.

Efforts involved attaching a light tether that restricts the drone until we know how the it flies, but what usually happens is that the tether gets trapped in a rotor, or the tether gets tight and the drone freaks out and crashes into the ground.

Using a gimbal is far more elegant, because it allows the drone to rotate freely in three dimensions, so the basic features of the drone can be established before you let it loose in the skies.

The gimbal was designed with the CrazyFlie in mind, but as there’s nothing more exotic holding the craft down than a zip tie, it should work with similarly sized quadcopters.

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Exploring Ground-Effect With A Quadcopter

The ground-effect (GE) refers to the almost mystical property where the interaction of the airflow around an aircraft’s wing and the ground massively increases efficiency due to the reduction of lift-dependent drag, perhaps best demonstrated by the Soviet Lun-class “ekranoplans” of the 1980s and 90s. Interestingly, this principle also applies to rotary aircraft, which led the [rctestflight] YouTube channel to wonder what would happen if a quadcopter were to be adapted for GE.

As noted on the Wikipedia entry for Ground-effect vehicle (GEV), it’s essential to have some kind of forward motion. With a rotorcraft like a helicopter or quadcopter this motion is already provided by the spinning propeller, which makes it noticeably easier to get the aircraft into the ground-effect. operating mode. Following the notion that the GE becomes noticeable at an altitude that’s dependent on the length of the aircraft’s wings, this got translated into putting the largest propellers available on the custom inverted-prop (to put them lower to the ground) quadcopter, to see what effect this would have on the quadcopter’s performance. As demonstrated by the recorded current drawn (each time with a fully charged battery), bigger is indeed better, and the GE effect is indeed very noticeable for a quadcopter.

Getting a usable GEV out of the basic inverted-prop quadcopter required some more lateral thinking, however, as it was not very easy to control this low to the ground. Here following design cues from skirtless hovercraft designs helped a lot, essentially drawing on the Coandă effect. Although this improved performance, at this point the quadcopter had been fitted with a fifth propeller for propulsion and was skidding about more like a skirtless hovercraft and less of a quadcopter.

Although great for scaring the living daylights out of unsuspecting water-based wildlife, what this unfortunately demonstrates is that GEVs are still hard, no matter which form they take. At the very least it does make for an excellent introduction into various aspects of aerodynamics.

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Hefty 3D Printed Quadcopter Meets Nasty End

You can readily buy all kinds of quadcopters off the shelf these days, but sometimes it’s more fun to build your own. [Michael Rechtin] did just that, with a hefty design of his own creation.

The build is an exploration of all kinds of interesting techniques. The frame itself uses generative design techniques to reduce weight while maintaining strength, while the motors themselves make heavy use of 3D-printed components. The design is modular and much of it slots together, too, and it uses a homebrewed flight controller running dRehmflight. It draws 2.5 kW from its lithium polymer batteries and weighs over 5 kg.

The DIY ethos led to some hurdles, but taught [Michael] plenty along the way. Tuning the PID control loop posed some challenges, as did one of the hand-wound motors being 5% down on thrust.  Eventually, though, the quad flew well enough to crash into a rectangular gate, before hitting the ground. Any quad pilot will tell you that these things happen. Drilling into the quad with a battery still inside then led to a fire, which did plenty of further damage.

[Michael’s] quad doesn’t appear to be specifically optimized to any one task, and it’s easy to see many ways in which it could be lightened or otherwise upgraded. However, as a freeform engineering thinking exercise, it’s interesting to watch as he tackles various problems and iteratively improves the design. Video after the break.

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Automated Drone Takes Care Of Weeds

Commercial industrial agriculture is responsible for providing food to the world’s population at an incredibly low cost, especially when compared to most of human history when most or a majority of people would have been involved in agriculture. Now it’s a tiny fraction of humans that need to grow food, while the rest can spend their time in cities and towns largely divorced from needing to produce their own food to survive. But industrial agriculture isn’t without its downsides. Providing inexpensive food to the masses often involves farming practices that are damaging to the environment, whether that’s spreading huge amounts of synthetic, non-renewable fertilizers or blanket spraying crops with pesticides and herbicides. [NathanBuildsDIY] is tackling the latter problem, using an automated drone system to systemically target weeds to reduce his herbicide use.

The specific issue that [NathanBuildsDIY] is faced with is an invasive blackberry that is taking over one of his fields. To take care of this issue, he set up a drone with a camera and image recognition software which can autonomously fly over the field thanks to Ardupilot and a LiDAR system, differentiate the blackberry weeds from other non-harmful plants, and give them a spray of herbicide. Since drones can’t fly indefinitely, he’s also build an automated landing pad complete with a battery swap and recharge station, which allows the drone to fly essentially until it is turned off and uses a minimum of herbicide in the process.

The entire setup, including drone and landing pad, was purchased for less than $2000 and largely open-source, which makes it accessible for even small-scale farmers. A depressing trend in farming is that the tools to make the work profitable are often only attainable for the largest, most corporate of farms. But a system like this is much more feasible for those working on a smaller scale and the automation easily frees up time that the farmer can use for other work. There are other ways of automating farm work besides using drones, though. Take a look at this open-source robotics platform that drives its way around the farm instead of flying.

Thanks to [PuceBaboon] for the tip!

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Fly Like You Drive With This Flying RC Drift Car

So it’s 2023, and you really feel like we should have flying cars by now, right? Well, as long as you ignore the problem of scale presented by [Nick Rehm]’s flying RC drift car, we pretty much do.

At first glance, [Nick]’s latest build looks pretty much like your typical quadcopter. But the design has subtle differences that make it more like a car without wheels. The main difference is the pusher prop at the aft, which provides forward thrust without having to pitch the entire craft. Other subtle clues include the belly-mounted lidar and nose-mounted FPV camera, although those aren’t exactly unknown on standard UAVs.

The big giveaway, though, is the RC car-style remote used to fly the drone. Rather than use the standard two-joystick remote, [Nick] rejiggered his dRehmFlight open-source flight control software to make operating the drone less like flying and more like driving. The lidar is used to relieve the operator of the burden of altitude keeping by holding the drone at about a meter or so off the deck. And the video below shows it doing a really good job of it, for the most part — with anything as complicated as the multiple control loops needed to keep this thing in the air, it’s easy for a sudden input to confuse things.

We have to admit that [Nick]’s creation looks like a lot of fun to fly, or drive — whichever way you want to look at it. Either way, we like the simplification of the flight control system and translating the driving metaphor into flying — it seems like that’ll be something we need if we’re ever to have full-size flying cars.

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UAV Flight Controller Saves Weight

When building autonomous airborne vehicles like drones or UAVs, saving a little bit of weight goes a long way, literally. Every gram saved means less energy needed to keep the aircraft aloft and ultimately more time in the air, but unmanned vehicles often need to compromise some on weight in order to carry increased computing abilities. Thankfully this one carries a dizzying quantity of computer power for an absolute minimum of weight, and has some clever design considerations to improve its performance as well.

The advantage of this board compared to other similar offerings is that it is built to host a Raspberry Pi Compute Module 4, while the rest of the flight controllers are separated out onto a single circuit board. This means that the Pi is completely sandboxed from the flight control code, freeing up computing power on the Pi and allowing it to run a UAV-specific OS like OpenHD or RubyFPV. These have a number of valuable tools available for unmanned flight, such as setting up a long range telemetry and camera links. The system itself supports dual HD camera input as well as additional support for other USB devices, and also includes an electronic speed controller mezzanine which has support for quadcopters and fixed wing crafts.

Separating non-critical tasks like cameras and telemetry from the more important flight controls has a number of benefits as well, including improved reliability and simpler software and program design. And with a weight of only 30 grams, it won’t take too much cargo space on most UAVs. While the flight computer is fairly capable of controlling various autonomous aircraft, whether it’s a multi-rotor like a quadcopter or a fixed wing device, you might need a little more computing power if you want to build something more complicated.

Screenshot of the SDR software in action, with decoded data in a terminal, and a map that shows the location received from the decoded data

Loudmouth DJI Drones Tell Everyone Where You Are

Back when commercial quadcopters started appearing in the news on the regular, public safety was a talking point. How, for example, do we keep them away from airports? Well, large drone companies didn’t want the negative PR, so some voluntarily added geofencing and tracking mechanisms to their own drones.

When it comes to DJI, one such mechanism is DroneID: a beacon on the drone itself, sending out a trove of data, including its operator’s GPS location. DJI also, of course, sells the Aeroscope device that receives and decodes DroneID data, declared to be for government use. As it often is with privacy-compromising technology, turns out it’s been a bigger compromise than we expected.

Questions started popping up last year, as off-the-shelf quadcopters (including those made by DJI) started to play a part in the Russo-Ukrainian War. It didn’t take long for Ukrainian forces to notice that launching a DJI drone led to its operators being swiftly attacked, and intel was that Russia got some Aeroscopes from Syria. DJI’s response was that their products were not meant to be used this way, and shortly thereafter cut sales to both Russia and Ukraine.

But security researchers have recently discovered the situation was actually worse than we expected. Back in 2022, DJI claimed that the DroneID data was encrypted, but [Kevin Finisterre]’s research proved that to be a lie — with the company finally admitting to it after Verge pushed them on the question. It wouldn’t even be hard to implement a worse-than-nothing encryption that holds up mathematically. However, it seems, DroneID doesn’t even try: here’s a GitHub repository with a DroneID decoder you can use if you have an SDR dongle.

Sadly, the days of companies like DJI standing up against the anti-copter talking points seem to be over, Now they’re setting an example on how devices can subvert their owners’ privacy without reservation. Looks like it’s up to hackers on the frontlines to learn how to excise DroneID, just like we’ve done with the un-nuanced RF power limitations, or the DJI battery DRM, or transplanting firmware between hardware-identical DJI flight controller models.

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