Hackaday Prize Entry: Electric Variable Pitch Props

Barring the smallest manned airplanes, most aircraft that are pulled around by a prop have variable pitch propellers. The reason for this is simple efficiency. Internal combustion engines are most efficient at a specific RPM, and instead of giving the engine more gas to speed up, pilots can simply change the pitch of a propeller. With a gas powered engine, the mechanics and design of variable pitch propellers are well understood and haven’t really changed much in decades. Adding variable pitch props to something pulled around by an electric motor is another matter entirely. That’s what [Peter McCloud] is building for his entry to the Hackaday Prize, and it’s going into the coolest project imaginable.

This project is designed for a previous Hackaday Prize entry, and the only 2014 Hackaday Prize entry that hasn’t killed anyone yet. Goliath is a quadcopter powered by a lawnmower engine, and while it will hover in [Peter]’s test rig, he’s not getting the lift he expected and the control system needs work. There are two possible solutions to the problem of controlling the decapatron: an ingenious application of gimballed grid fins, or variable pitch rotors. [Peter] doesn’t know if either solution will work, so he’s working on both solutions in parallel.

[Peter]’s variable pitch rotor system is basically an electronic prop mount that connects directly to the driven shafts on his gas-powered quadcopter. To get power to the electronics, [Peter] is mounting permanent magnets to the quad’s frame, pulling power from coils in the rotor hub, and rectifying it to DC to drive the servos and electronics. Control of the props will be done wirelessly through an ESP32 microcontroller.

Variable pitch props are the standard for everything from puddle jumpers to acrobatic RC helis. In the quadcopter world, variable pitch props are at best a footnote. The MIT ACL lab has done something like this, but perhaps the best comparison to what [Peter] is doing is the incredible Stingray 500 quad. Flite Test did a great overview of this quad (YouTube), and it’s extremely similar to a future version of the Goliath. A big motor (in the Stingray’s case, a brushless motor) powers all the props via a belt, and the pitch of the props is controlled by four servos. The maneuverability of these variable pitch quads is unbelievable, but since the Goliath is so big and has so much mass, it’s doubtful [Peter] will be doing flips and rolls with his quads.

You can check out a video of [Peter]’s build below.

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Welcome to the Drone Wars

DroneClash” is a competition to be held on December 4th (save the date!) in a hangar at Valkenburg airfield in the Netherlands. The game? Teams try to destroy each others’ quadcopters, navigate through a “Hallway of Doom, Death, and Destruction”, and finally enter a final phase of the game where they try to defend their “queen” drone while taking out those of their opponents.

This sounds like crazy and reckless fun. Surprisingly, it’s being sponsored by the Technical University of Delft’s Micro Air Vehicle (MAV) lab. The goal is to enable a future of responsible drone use by having the ability “to take them out if necessary”.

Drone development has grown hugely in recent years, and you can see the anti-drone industry growing too. Ideally, these developments keep each other in check and result in a safe and responsible incorporation of drones in our daily lives. We are organising DroneClash to generate new ideas in order to encourage this process.

We do have to ask ourselves why anyone would want to use another quadcopter to take out illegally operated quadcopters — there must be a million more effective means from a policing standpoint.  On the other hand, if we were re-shooting “Hackers” right now, and looking for a futuristic sport, we would swap out rollerblading for drone combat. Registration opens this week. Gentlebots, start your engines.

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Frankenquad takes to the air

Modern quadcopter flight controllers perform a delicate dance of balancing pitch, yaw, bank, and throttle. They can do this thanks to modern MEMS gyros and accelerometers. The job is easy when the motors, propellers and speed controllers are relatively well matched. But what if they’re not? That’s the questions [SkitzoFPV] set out to answer by building Frankenquad.  Frankenquad is a 250 sized FPV quadcopter with 4 different motors and 4 different propellers. The props are different sizes from different manufacturers, and even include a mix of 3 and 4 blade units. If all that wasn’t enough [SkitzoFPV] used 3 different electronic speed controller. Each speed controller has a micro running different firmware, meaning it will respond slightly differently to throttle inputs.

Keeping all this in check was [SkitzoFPV’s] branded version of the Raceflight Revolt R4 flight controller. The Revolt is powered by an STM32F4 series ARM microcontroller. Most of these controllers run variants of the cleanflight open source flight control software. The question was – would it be able to handle the unbalanced thrust and torque of 4 different power combinations?

The flight tests proved the answer was a resounding yes. The quad hovered easily. As the video shows [SkitzoFPV] went on to burn a few holes in the sky with it. Admittedly [SkitzoFPV] is a much better pilot than any of us. He did notice a bit of a bobble and a definite yaw toward the smaller propeller. Still, it’s rather amazing how easily a modern flight controller was able to turn a pile of junk-box components into a flying quadcopter. You can learn more about flight controllers right here.

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The World’s Lightest Brushless FPV Quadcopter

When a claim is made for something being the world’s lightest it is easy to scoff, after all that’s a bold assertion to make. It hasn’t stopped [fishpepper] though, who claims to have made the world’s lightest brushless FPV quadcopter. Weighing in at 32.4 grams (1.143 oz) it’s certainly pretty light.

The frame is a circular design cut from carbon-fiber-reinforced polymer, and on it are mounted four tiny brushless motors. In the center are the camera and battery on a 3D printed mount, as well as custom flight and speed controller boards. There are a series of posts detailing some of the design steps, and the result is certainly a capable aircraft for something so tiny. If you fancy experimenting with the design yourself, the files are available for download on the first page linked above.

There are two aspects to this build that make it interesting to us. First, the lightest in the world claim. We think someone will come along with something a bit lighter, and we can’t wait to see a lightest multirotor arms race. Good things come of technology races, which brings us to the second aspect. Governments are busy restricting the use of larger multirotors, to the extent that in some parts of the world all that will be available for non professionals will be sub-200g toy craft. Any project like this one which aims to push the boundaries of what is possible with smaller multirotors is thus extremely interesting, and we hope the community continue to innovate in this direction if only to make a mockery of any restrictions.

To get some idea of the sort of legislative measures we might be seeing, take a look at our coverage of a consultation in just one country.

Lighthouse Locates Drone; Achieves Autonomous Battery Swap

The HTC Vive’s Lighthouse localization system is one of the cleverest things we’ve seen in a while. It uses a synchronization flash followed by a swept beam to tell any device that can see the lights exactly where it is in space. Of course, the device has to understand the signals to figure it out.

[Alex Shtuchkin] built a very well documented device that can use these signals to localize itself in your room. For now, the Lighthouse stations are still fairly expensive, but the per-device hardware requirements are quite reasonable. [Alex] has the costs down around ten dollars plus the cost of a microcontroller if your project doesn’t already include one. Indeed, his proof-of-concept is basically a breadboard, three photodiodes, op-amps, and some code.

His demo is awesome! Check it out in the video below. He uses it to teach a quadcopter to land itself back on a charging platform, and it’s able to get there with what looks like a few centimeters of play in any direction — more than good enough to land in the 3D-printed plastic landing thingy. That fixture has a rotating drum that swaps out the battery automatically, readying the drone for another flight.

If this is just the tip of the iceberg of upcoming Lighthouse hacks, we can’t wait!

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Anti-Drone Fence: Science or Snakeoil?

Remember when it was laser pointers? Well, now it’s drones.

[Thinkerer] sent us this link to what’s essentially a press release for a company called Sensofusion that makes a UAV detector and (they claim) smart jammer, and apparently one is being installed at Denver International airport.

We buy that the “Airfence” system will be able to detect known systems by signature, and possibly even take them over. We’ve seen two exploits of quadcopter radio protocols (one a timing attack and the other a controller ID spoof) that would allow them to do just that. But is that the problem? Don’t most of the major manufacturers fence off airports in software these days anyway? And are drones really the droids that you’re looking for?

They also make some claims about being able to detect and stop DIY copters, but we don’t see how. Imagine that your copter ran encrypted on 2.4 GHz. How is this different from any other WiFi signal? Or imagine that it sends and receives infrequent data in the congested pager bands? And short of jamming, we don’t see how they’re going to take down anything that they don’t already understand.

So, commenteers, how would you do it? Detect and even take over an arbitrary drone? Possible or snakeoil?

Helicopter Pendulum is PID-licious

If you’ve ever tried to tune a PID system, you have probably encountered equal parts overwhelming math and black magic folk wisdom. Or maybe you just let the autotune take over. If you really want to get some good intuition for motion control algorithms, PID included, nothing beats a little hands-on experimentation.

To get you started, [Clovis] wrote in with his budget propeller-based PID demo platform (Portuguese, translated shockingly well here).

The basic setup is a potentiometer glued to a barbecue skewer with a mini-quadcopter motor and rotor on the end of it. A microcontroller reads the voltage and PWMs the propeller through a MOSFET. The goal is to have the pendulum hover stably in midair, controlled by whatever algorithms you can dream up on the controller. [Clovis]’ video demonstrates on-off and PID control of the fan. Adding a few more potentiometers (one for P, I, and D?) would make hands-on tweaking even more interactive.

In all, it’s a system that will only set you back a few bucks, but can teach you more than you’d learn in a month in college. Chances are good that you’re not going to have exactly the same brand of sardine can on hand that he did, but some improvisation is called for here.

If you don’t know why you’d like to master open-loop closed-loop control algorithms, here’s one of the best advertisements that we’ve seen in a long time. But you don’t have to start out with hand-wound hundred-dollar motors, or precisely machined bits. As [Clovis] demonstrates, you can make do with a busted quadcopter and whatever you find in your kitchen.

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