Small Feathers, Big Effects: Reducing Stall Speeds With Strips Of Plastic

December 2, 2024 by Danie Conradie 18 Comments

Birds have long been our inspiration for flight, and researchers at Princeton University have found a new trick in their arsenal: covert feathers. These small feathers on top of birds’ wings lay flat during normal flight but flare up in turbulence during landing. By attaching flexible plastic strips – “covert flaps” – to the top of a wing, the team has demonstrated impressive gains in aircraft performance at low speeds.

Wind tunnel tests and RC aircraft trials revealed a fascinating two-part mechanism. The front flaps interact with the turbulent shear layer, keeping it close to the wing surface, while the rear flap create a “pressure dam” that prevents high-pressure air from moving forward. The result? Up to 15% increase in lift and 13% reduction in drag at low speeds. Unfortunately the main body of the paper is behind a paywall, but video and abstract is still fascinating.

This innovation could be particularly valuable during takeoff and landing – phases where even a brief stall could spell disaster. The concept shares similarities with leading-edge slats found on STOL aircraft and fighter jets, which help maintain control at high angles of attack. Imitating feathers on aircraft wings can have some interesting applications, like improving control redundancy and efficiency.

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Experimental Drone Flies Like A Bird

November 25, 2024 by Danie Conradie 11 Comments

Most RC planes follow a simple control scheme: elevators for pitch, rudder for yaw, and ailerons for roll. This one-to-one mapping keeps things straightforward, and fewer actuators means less weight. But nature has other ideas. Birds achieve flight control through complex, coordinated movements where different body parts can affect multiple degrees of freedom simultaneously. Now, researchers at EPFL have brought this biological approach to robotics with the LisEagle, a drone featuring morphing wings and tail that demonstrate remarkable stability.

All the control surfaces and actuators — All the actuators!

The LisEagle packs seven different actuation methods alongside its nose-mounted motor. Three of these control the bird-like wingtips and spreading tail, while the remaining actuators handle more conventional controls: independently twisting wing bases (similar to ailerons) and a tail assembly that combines elevator and rudder functions in its vertical stabilizer.

Testing took place in controlled indoor conditions, with the maintaining position in front of an open wind tunnel. Optical position tracking provided closed-loop feedback and power was provided via a tether to minimize weight. A PID flight controller orchestrated all seven actuators in concert, achieving impressive stability even when faced with induced turbulence or being poked with a stick. In a demonstration of redundancy, the researchers deliberately disabled the twisting wing mechanisms, and the aircraft maintained control using just its wingtips and tail.

The team went further, employing Bayesian optimization to find the most efficient actuator combinations. This revealed potential energy savings of up to 11%, with optimal configurations varying based on airspeed as lift requirements changed.

While research into the flight mechanisms of bees, bats and birds might not immediately translate to practical applications, it deepens our understanding of flight control principles. Don’t be surprised if morphing wings become a more common sight in future aircraft designs.

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Modular Multi-Rotor Flies Up To Two Hours

November 24, 2024 by Danie Conradie 28 Comments

Flight time remains the Achilles’ heel of electric multi-rotor drones, with even high-end commercial units struggling to stay airborne for an hour. Enter Modovolo, a startup that’s shattered this limitation with their modular drone system achieving flights exceeding two hours.

The secret? Lightweight modular “lift pods” inspired by bicycle wheels using tensioned lines similar to spokes. The lines suspend the hub and rotor within a duct. It’s all much lighter than of traditional rigid framing. The pods can be configured into quad-, hex-, or octocopter arrangements, featuring large 671 mm propellers. Despite their size, the quad configuration weighs a mere 3.5 kg with batteries installed. From the demo-day video, it appears the frame, hub, and propeller are all FDM 3D printed. The internal structure of the propeller looks very similar to other 3D-printed RC aircraft.

The propulsion system operates at just 1000 RPM – far slower than conventional drones. The custom propellers feature internal ring gears driven by small brushless motors through a ~20:1 reduction. This design allows each motor to hover at a mere 60 W, enabling the use of high-density lithium-ion cells typically unsuitable for drone applications. The rest of the electronics are off-the-shelf, with the flight controller running ArduPilot. Due to the unconventional powertrain and large size, the PID tuning was very challenging.

We like the fact this drone doesn’t require fancy materials or electronics, it just uses existing tech creatively. The combination of extended flight times, rapid charging, and modular construction opens new possibilities for applications like surveying, delivery, and emergency response where endurance is critical.

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Transforming Drone Drives And Flies

November 22, 2024 by Danie Conradie 8 Comments

Vehicles that change their shape and form to adapt to their operating environment have long captured the imagination of tech enthusiasts, and building one remains a perennial project dream for many makers. Now, [Michael Rechtin] has made the dream a bit more accessible with a 3D printed quadcopter that seamlessly transforms into a tracked ground vehicle.

The design tackles a critical engineering challenge: most multi-mode vehicles struggle with the vastly different rotational speeds required for flying and driving. [Michael]’s solution involves using printed prop guards as wheels, paired with lightweight tracks. An extra pair of low-speed brushless motors are mounted between each wheel pair, driving the system via sprockets that engage directly with the same teeth that drive the tracks.

The transition magic happens through a four-bar linkage mounted in a parallelogram configuration, with a linear actuator serving as the bottom bar. To change from flying to driving configuration the linear actuator retracts, rotating the wheels/prop guards to a vertical position. A servo then rotates the top bar, lifting the body off the ground. While this approach adds some weight — an inevitable compromise in multi-purpose machines — it makes for a practical solution.

Powering this transformer is a Teensy 4.0 flight controller running dRehmFlight, a hackable flight stabilization package we’ve seen successfully adapted for everything from VTOLs to actively stabilized hydrofoils. Continue reading “Transforming Drone Drives And Flies” →

Automated Weed Spraying Drone Needs No Human Intervention

November 11, 2024 by Danie Conradie 4 Comments

Battling weeds can be expensive, labor intensive and use large amounts of chemicals. To help make this easier [NathanBuilds] has developed V2 of his open-source drone weed spraying system, complete with automated battery swaps, herbicide refills, and an AI vision system for weed identification.

The drone has a 3D printed frame, doubling as a chemical reservoir. V1 used a off-the-shelf frame, with separate tank. Surprisingly, it doesn’t look like [Nathan] had issues with leaks between the layer lines. For autonomous missions, it uses ArduPilot running on a PixHawk, coupled with RTK GPS for cm-level accuracy and a LiDAR altimeter. [Nathan] demonstrated the system in a field where he is trying to eradicate invasive blackberry bushes while minimizing the effect on the native prairie grass. He uses a custom image classification model running on a Raspberry Pi Zero, which only switches on the sprayers when it sees blackberry bushes in the frame. The Raspberry Pi Global Shutter camera is used to get blur-free images.

At just 305×305 mm (1×1 ft), the drone has limited herbicide capacity, and we expect the flights to be fairly short. For the automated pit stops, the drone lands on a 6×8 ft pad, where a motorized capture system pulls the drone into the reload bay. Here a linear actuator pushes a new battery into the side of the drone while pushing the spend battery one out the other side. The battery unit is a normal LiPo battery in 3D-printed frame. The terminal are connected to copper wire and tape contacts on the outside the battery unit, which connect to matching contacts in the drone and charging receptacles. This means the battery can easily short if it touches a metal surface, but a minor redesign could solve this quickly. There are revolving receptacles on either side of the reload bay, which immediately start charging the battery when ejected from the drone.

Developing a fully integrated system like this is no small task, and it shows a lot of potential. It might look a little rough around the edges, but [Nathan] has released all the design files and detailed video tutorials for all the subsystems, so it’s ready for refinement.

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Amazon Receives FAA Approval For MK30 Delivery Drone

November 6, 2024 by Maya Posch 23 Comments

It’s been about a decade since Amazon began to fly its delivery drones, aiming to revolutionize the online shopping experience with rapid delivery of certain items. Most recently Amazon got permission from the FAA to not only start flying from its new Arizona-based location, but also to fly beyond-visual-line-of-sight (BVLOS) missions with the new MK30 drone. We reported on this new MK30 drone which was introduced earlier this year along with the news of the Amazon Prime Air delivery service ceasing operations in California and moving them to Arizona instead.

This new drone has got twice the range as the old MK27 drone that it replaces and is said to be significantly quieter as well. The BLOS permission means that the delivery drones can service areas which are not directly visible from the warehouse with its attached drone delivery facility. With some people within the service range of the MK27 drones having previously complained about the noise levels, we will see quickly enough whether the MK30 can appease most.

As for the type of parcels you can have delivered with this service, it is limited to 2.27 kg (~5 lbs), which is plenty for medication and a range of other items where rapid delivery would be desirable.

Custom Drone Software Searches, Rescues

October 24, 2024 by Bryan Cockfield 17 Comments

When a new technology first arrives in people’s hands, it often takes a bit of time before the full capabilities of that technology are realized. In much the same way that many early Internet users simply used it to replace snail mail, or early smartphones were used as more convenient methods for messaging and calling than their flip-phone cousins, autonomous drones also took a little bit of time before their capabilities became fully realized. While some initially used them as a drop-in replacement for things like aerial photography, a group of mountain rescue volunteers in the United Kingdom realized that they could be put to work in more efficient ways suited to their unique abilities and have been behind a bit of a revolution in the search-and-rescue community.

The first search-and-rescue groups using drones to help in their efforts generally used them to search in the same way a helicopter would have been used in the past, only with less expense. But the effort involved is still the same; a human still needed to do the searching themselves. The group in the UK devised an improved system to take the human effort out of the equation by sending a drone to fly autonomously over piece of mountainous terrain and take images of the ground in such a way that any one thing would be present in many individual images. From there, the drone would fly back to its base station where an operator could download the images and run them through a computer program which would analyse the images and look for outliers in the colors of the individual pixels. Generally, humans tend to stand out against their backgrounds in ways that computers are good at spotting while humans themselves might not notice at all, and in the group’s first efforts to locate a missing person they were able to locate them almost immediately using this technology.

Although the system is built on a mapping system somewhat unique to the UK, the group has not attempted to commercialize the system. MR Maps, the software underpinning this new feature, has been free to use for anyone who wants to use it. And for those just starting out in this field, it’s also worth pointing out that location services offered by modern technologies in rugged terrain like this can often be misleading, and won’t be as straightforward of a solution to the problem as one might think.