High-Speed RC Car Needs A Flight Controller

The fastest ground vehicles on earth are not driven by their wheels but by an aircraft jet engine. At world record speeds, they run on an aerodynamic razor’s edge between downforce, which limits speed, and liftoff, which can result in death and destruction. [rctestflight] wanted to see what it takes to run an RC car at very high speeds, so he built a ducted-fan powered car with aerodynamic control surfaces and an aircraft flight controller.

This high-speed car is built on the chassis of a 1/14th scale RC buggy, powered by 4 EDF (electric ducted fans) mounted on a very long aerodynamic foam board shell. It also has an aircraft-style tail with elevons and rudders for stabilization and control at high speed using an ArduPilot flight controller. The flight controller is set up to stabilize in the roll and yaw axis, with only fixed trim in the pitch axis.

[rctestflight] got the car up to 71 MPH (114 km/h), which is fast for most RC cars but well short of the 202 MPH RC car speed record. It was still quite hard to keep in a straight line, and the bumpy roads certainly didn’t help. He hopes to revisit the challenge in the future with larger motors and high voltage batteries.

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Solar Plane Might Be Able To Last Through The Night

“Just add solar panels to the wings” is a popular suggestion for improving the flight times of fixed-wing drones. However, the reality is not so simple, and it’s easy to hurt rather than help flight times with the added weight and complexity. The team at [Bearospace Industries] has been working on the challenge for the while, and their Solar Dragon aircraft recently had a very successful test flight, producing about 50% more power than it was consuming.

Instead of just trying to slap solar panels to an existing plane, an airframe should ideally be designed from the ground up as a balancing act between a range of factors. These include weight, efficiency, flight envelope, structural integrity, and maximum surface area for solar panels. All the considerations are discussed by [Bearospace] in an excellent in-depth video, which is an indispensable resource for anyone planning to build a solar plane.

[Bearospace] put all the theory into practice on Solar Dragon, which incorporates over 250 W of high-efficiency Maxeon C60 solar cells on the wing, tail, and triangular fuselage. The cells were wired to match their maximum power point voltage as closely as possible to the plane’s 3S lithium-ion battery pack, enabling the solar cells to charge the battery directly. To prevent overcharging, a solid state relay was used to disconnect the solar cells from the battery as required.

The batteries maintained the same average state of charge during the entire one-hour late morning flight, even though the panels were only connected 65% of the time. The team expects they might be able to get even better performance from the cells with a good MPPT charger, which will be required for less than ideal solar conditions.

Solar Dragon has a much larger payload capacity than was used during the test flight, more than enough for an MPPT charger and a significantly larger battery. With this and a long list of other planned improvements, it might be possible for the Solar Dragon to charge up during the day and fly throughout the night on battery power alone. One interesting potential approach mentioned is to also store energy in the form of altitude during the day, and use the aircraft’s slow sink rate to minimize battery usage at night.

Solar planes come up every few months on Hackaday, with [rctestflight] being one of the usual suspects. You also don’t need solar panels for long flight times, as [Matthew Heiskell] proved with a 10-hour 45 minute flight on battery power alone.

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The Unique Challenges Of Aerial Robotics

When we think of robotics, the first thing that usually comes to mind for many of us is some sort of industrial arm that’s bolted to the floor, or perhaps a semi-autonomous rover trudging its way across the dusty Martian landscape. While these two environments are about as different as can be, the basic “rules” are pretty much the same. Being on firm ground ground gives the robot a clear understanding of its position and orientation, which greatly simplifies tasks such as avoiding collisions or interacting with nearby objects.

But what happens when that reference point goes away? How does a robot navigate when it’s flying through open space or hovering in mid-air? That’s just one of the problems that fascinates Nick Rehm, who stopped by to host this week’s Aerial Robotics Hack Chat to talk about his passion for flying robots. He’s currently an aerospace engineer at Johns Hopkins Applied Physics Laboratory, where he works on the unique challenges faced by autonomous flying vehicles such as the detection and avoidance of mid-air collisions, as well as the development of vertical take-off and landing (VTOL) systems. But before he had his Master’s in Aerospace Engineering and Rotorcraft, he got started the same way many of us did, by playing around with DIY projects.

In fact, regular Hackaday readers will likely recall seeing some of his impressive builds. His autonomous ekranoplan designed to follow a target using computer vision graced the front page in April. Back in 2020, we took a look at his recreation of SpaceX’s Starship prototype, which used a realistic arrangement of control surfaces and vectored thrust to perform the spacecraft’s signature “Belly Flop” maneuver — albeit with RC motors and propellers instead of rocket engines. But even before that, Nick recalls asking his mother for permission to pull apart a Wii controller so he could use its inertial measurement unit (IMU) in a wooden-framed tricopter he was working on.

Discussing some of these hobby builds leads the Chat towards Nick’s dRehmFlight project, a GPLv3 licensed flight control package that can run on relatively low-cost hardware, namely a Teensy 4.0 microcontroller paired with the GY-521 MPU6050 IMU. The project is designed to let hobbyists easily experiment with VTOL craft, specifically those that transition between vertical and horizontal flight profiles, and has powered the bulk of Nick’s own flying craft.

Moving onto more technical questions, Nick says one of the most difficult aspects when designing an autonomous flying vehicle is getting your constraints nailed down. What he means by that is having a clear goal of what the craft needs to do, and critically, how long it needs to do it. How far does the craft need to be able to fly? How fast? Does it need to loiter at the target location, and if so, for how long? The answers to these questions will largely dictate the form of the final vehicle, and are key to determining if it’s worth implementing the complexity of transitioning from VTOL to fixed-wing horizontal flight.

But according to Nick, the biggest challenge in aerial robotics is onboard state estimation. That is, the ability for the craft to know its position and orientation relative to the ground. While high-performance computers have gotten lighter and sensors have improved, he says there’s still no substitute for having a ground-based tracking system. He mentions that those fancy demonstrations you’ve seen with drones flying in formation and working collaboratively towards a task will almost certainly have an array of motion capture cameras tucked off to the side. This makes for an impressive show, but greatly limits the practical application of these drone swarms.

Nick’s custom Raspberry Pi 4-powered quadcopter lets him test autonomous flight techniques.

So what does the future of aerial robotics look like? Nick says open source projects like ArduPilot and PX4 are still great choices for hobbyists, but sees promise in newer platforms which pair the traditional autopilot with more onboard computing power, such as Auterion’s Skynode. More powerful flight controllers can enable techniques such as simultaneous localization and mapping (SLAM), which uses 3D scans of the environment to help the robot orient itself. He’s also very interested in technologies that enable autonomous flight in GPS-denied environments, which is critical for robotic craft that need to operate indoors or in situations where satellite navigation is unavailable or unreliable. In light of the incredible success of NASA’s Ingenuity helicopter, we imagine these techniques will also play an invaluable role in the future airborne exploration of Mars.

We want to thank Nick for hosting this week’s Aerial Robotics Hack Chat, which turned out to be one of the fastest hours in recent memory. His experience as both an avid hobbyist and a professional in the field provided exactly the sort of insight the Hackaday community looks for, and his gracious offer to keep in touch with several of those who attended the Chat to further discuss their projects speaks to how passionate he is about this topic. We expect to see great things from Nick going forward, and would love to have him join us again in the future to see what he’s been up to.

The Hack Chat is a weekly online chat session hosted by leading experts from all corners of the hardware hacking universe. It’s a great way for hackers connect in a fun and informal way, but if you can’t make it live, these overview posts as well as the transcripts posted to Hackaday.io make sure you don’t miss out.

Autonomous Inflatable Canoe

With the summer months nearly upon us, many are dreaming of warm afternoons spent floating on a quiet lake. Unless you’re [Kolins] anyway. Apparently his idea of a good time is controlling a full-sized inflatable canoe not from onboard with a pair of oars, but from the shore with a RC transmitter.

The linkage design allows the motor to be adjusted vertically.

Of course, as the video after the break shows, just because the canoe is powered by a remotely operated electric trolling motor doesn’t mean it can’t still carry human occupants. In fact, with the addition of a Matek F405-Wing flight controller running the rover variant of ArduPilot, the boat can even take you on a little tour of the lake while you kick back and relax.

We like that this project took the path of least resistance wherever possible. Rather than trying to spin up his own custom propulsion unit, and inevitably dealing with the challenge of waterproofing it, [Kolins] built his system around a commercial trolling motor. A clever servo mechanism physically turns the motor in much the same way a human operator would, while the speed is controlled with a suitably beefy ESC from Traxxas placed between the motor and its lead-acid battery.

It doesn’t look like there’s been any permanent mechanical or electrical changes made to the motor, which makes the whole thing a lot easier to replicate. We’ve talked in the past about the relative rarity of low-cost robotic watercraft, so a “bolt-on” propulsion module like this that can turn a cheap inflatable boat into an autonomous platform for research and experimentation is very interesting.

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the active foil flying across the water

Hydrofoils Love This One Simple Trick

Earlier in the year, [rctestflight] created an active hydrofoil RC craft but found the actual performance very lacking. Luckily for him and for us, he continued to tweak it and one tweak suddenly turned it from a nightmare to a dream.

That tweak was adding ArduPilot’s airplane model. The design had three servos, which each actuated the angle of a foil underneath one of the three pontoons. The ship propelled itself via some propellers mounted near the top. If you know much about ArduPilot, you notice that active hydrofoil boat doesn’t show up on the list of supported platforms, and you’re right. [rctestflight] points out that the three servos actually function as a plane underwater. The front two are ailerons and the back one is an elevator, all things that ArduPilot knows how to handle with a tightly controlled loop except for one thing; there’s no altitude data.

So he stole a trick he developed earlier for his ground effect plane and used a distance sensor to let ArduPilot know how to adjust things. He used a sonar sensor instead of lidar as it works better with water and he was pleasantly surprised when he took it out on the lake and it just worked wonderfully. The original goal with the active stabilization was to have the efoil immune to choppy waters, and we’re sad to say that it didn’t quite reach that lofty target. The single sonar sensor follows the wave in front of it beautifully but can’t handle the complex waves being thrown at it. Perhaps some sort of sensor fusion algorithm could provide the necessary data to be truly resilient. But we love watching the foil glide across the water and it is hard to remember that it’s actively flying rather than just floating that way.

Others have tried and failed to 3D print a hydrofoil while others have succeeded. We love that [rctestflight] came back to finish the fight and came away a champion. Video after the break.

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Autonomous Ground Effect Vehicle Demonstrator Aims To Speed Up Maritime Shipping

Ground effect vehicles, or ekranoplans, have the advantage of being more efficient than normal aircraft and faster than boats, but so far haven’t been developed beyond experimental prototypes. Fortunately, this doesn’t stop companies from trying, which has led to a collaboration between [ThinkFlight] and [rctestflight] to create a small-scale demonstrator for the Flying Ship Company.

The Flying Ship Company wants to use unmanned electric ekranoplans as high-speed marine cargo carriers that can use existing maritime infrastructure for loading and unloading. For the scale model, [rctestflight] was responsible for the electronics and software, while [ThinkFlight] built the airframe. As with his previous ekranoplan build, [ThinkFlight] designed it in XFLR5, cut the parts from foam using a CNC hot wire cutter (which we still want a better look at), and laminated it with Kevlar for strength. One of the challenges of ground effect vehicles is that the center of pressure will shift rearward as they leave a ground effect, causing them to pitch up. To maintain control when moving into and out of ground effect, these crafts often use a large horizontal stabilizer high up on the tail, out of ground effect.

A major feature of this demonstrator is automatic altitude control using a LIDAR sensor mounted on the bottom. This was developed by [rctestflight] using a simple foam board ekranoplan and [Think Flighs]’s previous airframe, with some custom code added to ArduPilot. It works very well on smooth, calm water, but waves introduce a lot of noise into the LIDAR data. It looks like they were able to overcome this challenge, and completed several successful test flights in calm and rough conditions.

The final product looks good, flies smoothly, and is easy to control since the pilot doesn’t need to worry about pitch or throttle control. It remains to be seen if The Flying Boat will overcome the challenges required to turn it into a successful commercial craft, and we will be following the project closely.

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Solar Powered Autonomous Tugboat For Rescuing Autonomous Vessels

[rctestflight] has built several autonomous boats, and with missions becoming longer and more challenging, he bought an inflatable kayak to serve as a dedicated rescue vessel. Instead of relying on outdated manual paddling, he built an autonomous solar-powered tugboat.

Towing test with kayak
♪ “Rum, treasure, ArduRover, Pixhawk 4 and so much solar, break of dawn till the day is over, the ship will surely go…” ♪

The tugboat uses a pair of molded fiberglass hulls in a catamaran configuration. The wide platform allows a pair of 100W solar panels to be mounted on top. It was [rctestflight]’s first time molding anything out of fiberglass, so there was quite a bit of trial and error going on. The mold was 3D printed in sections, aligned with dowel pins, and glued together. After the epoxy had cured, the mold halves could be split apart for easier removal of the hull.

As with most of [rctestflights] autonomous vehicles, control is handled by a Pixhawk 4 running ArduPilot/ArduRover. A pair of 76 mm brass propellers powered by brushless motors provide propulsion and differential steering. The motors get power from six LiFePO4 batteries, which charge from the solar panels via MPPT charge controllers. The hulls are covered with plywood decks with removable hatches and inspection windows. After a bit of tuning, he took the boat for a few test runs, the longest being 5.1 km with himself in tow in the kayak. At less than 5 km/h (3 mph) it’s no speedboat, but certainly looks like a relaxing ride. Many of [rctestflight]’s previous vessels were airboats to avoid getting underwater propellers tangled in weeds. It was less of an issue this time since he could just haul the tugboat close to the kayak and clear the propellers.

[rctestflights] are always entertaining and educational to watch, and this one certainly sets the standard for sea-shanty soundtracks at 13:32 in part two.

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