Sparkfun’s AVC 2014: Robots, Copters, and Red Balloons of Death, Oh My!


Registration is open for Sparkfun’s 2014 Autonomous Vehicle Competition (AVC)! Every year the fine folks at Sparkfun invite people to bring their robots, rovers, and drones  to Colorado to see who is the king of the hill – or reservoir as the case may be. We see plenty of robots here at Hackaday, but precious few of them are autonomous. To us that means capable of completing complex tasks without human intervention. Sparkfun has spent the last five years working toward changing that. Each year the robots get more complex and complete increasingly difficult tasks.

The competition is essentially a race through the Boulder reservoir. Time is key, though there are multiple ways to gain bonus points. For aerial vehicles there are two classes: fixed and rotary wing. Planes fall under the fixed wing category. Helicopters, gyrocopters, tricopters, quadcopters, and beyond fall into rotary wing. We’re holding out hope that e-volo shows up with their Octadecacopter. Ground vehicles have a few more class options. Micro/PBR class is for robots with a build cost less than $350 total, or small enough to fit into box that’s 10″x6″x4″. The doping class is unlimited. Sparkfun even mentions costs over $1kUSD+, and weights over 25LBS. Non-Traditional Locomotion class is for walkers, WildCats and the like. Peloton is Sparkfun’s class for robots that don’t fit into the other classes.

Sparkfun is also making a few changes to the course this year. A white chalk line will be drawn through the course, so robots don’t have to rely on GPS alone for navigation. We’re hoping to see at least a few vision systems using that chalk line. Aerial robots will have to contend with three “Red Balloons of Death”. Robots can navigate around the balloons without penalty. The balloons can be bumped or even popped for bonus points, but the robot must do this with its own body. Projectile weapons are not allowed. To say we’re excited about the AVC would be an understatement. As much as we enjoy watching the big players at competitions like the DARPA Robotics Challenge, we love seeing individuals and small teams of hobbyists compete every year at the AVC. Click on past the break for Sparkfun’s AVC 2013 wrap up video.

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Free Falling Quadcopter Experiments End With Splat


Don’t get too attached to the great picture up above, as the quad shooting it was in a death plunge when the frame was snapped. There’s just something tempting about free fall. Nearly every tri/quad/hex/multicopter pilot has the impulse to chop the throttle while flying around. Most quadcopters are fixed pitch, which means that as power drops, so does control authority. When power is cut, they fall like stones. A quick throttle chop usually results in a few feet of lost altitude and a quickened pulse for the pilot. Cut power for much longer than that, and things can get really interesting.  [RcTestFlight] decided to study free fall in depth, and modified a test bed quadcopter just for this purpose.

First, a bit of a primer on free-falling quadcopters and their power systems.  Quadcopters always have two motors spinning clockwise, and two spinning counterclockwise. This configuration counters torque and allows for yaw control. Most large quads these days use sensorless brushless motors, which can be finicky about startup conditions. Brushless controllers are generally programmed to kick a motor into spinning in the proper direction. If a motor is spinning in reverse at several hundred RPM, things can get interesting. There will often be several seconds of stuttering before the motor starts up, if it starts at all. The controller MOSFETS can even be destroyed in cases like this.

When a quadcopter loses power, the motors slow down and thrust drops off. The quad begins to drop. As the falling quadcopter picks up speed, the propellers begin to spin (windmill) due to the air rushing up from below. If the quadcopter started its fall in a normal attitude, all four of  the propellers will rotate reverse of its normal direction.  The now spinning props will actually act as something of an air brake, slowing the fall of the quad. This is similar to a falling maple seed, or autorotation in a helicopter.  The spinning blades will also act as gyroscopes, which will add some level of stabilization to the falling quadcopter. Don’t get us wrong – the quadcopter can still be unstable as it falls, generally bobbing and weaving through the air. None of this is a guarantee that the quad won’t tip over onto its back – which will reverse the entire process.  Through all of this bobbing, weaving, and falling the flight controller has been along for the ride. Most flight controllers we’ve worked with have not been programmed with free fall in mind, so there is no guarantee that they will come back on-line when the throttle is rolled on. Thankfully many controllers are open source, so testing and changes are only a matter of risking your quadcopter.

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Wireless Power Transfer for Quadrotors


Quadrotors are great, but what kind of range can you get on them, really? What if you could charge them up just by flying over high voltage power lines, by or temporarily hovering by a charging station? That’s just what [Dr. Carrick Detweiler] wrote a paper about! (Caution: PDF)

The paper discusses the method of wireless power transfer via magnetic resonance, which, depending on the scale, can transfer power at medium distances (~1 meter). This outperforms inductive coupling which requires a much closer proximity (~1-2 centimeters) for power to transfer. It does still require a certain amount of accuracy, but as we all know, quadrotors have no problem with even the most complex aerodynamic feats!

There is an excellent demonstration video of a small scale wireless quadrotor prototype after the break.

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SkyJack: A Drone to Hack All Drones


Quadcopters are gradually becoming more affordable and thus more popular; we expect more kids will unwrap a prefab drone this holiday season than any year prior. [Samy's] got plans for the drone-filled future. He could soon be the proud new owner of his own personal army now that he’s built a drone that assimilates others under his control.

The build uses a Parrot AR.Drone 2.0 to fly around with an attached Raspberry Pi, which uses everybody’s favorite Alfa adapter to poke around in promiscuous mode. If the SkyJack detects an IEEE-registered MAC address assigned to Parrot, aircrack-ng leaps into action sending deauthentication requests to the target drone, then attempts to take over control while the original owner is reconnecting. Any successfully lassoed drone doesn’t just fall out of the sky, though. [Samy] uses node-ar-drone to immediately send new instructions to the slave.

You can find all his code on GitHub, but make sure you see the video below, which gives a thorough overview and a brief demonstration. There are also a few other builds that strap a Raspberry Pi onto a quadcopter worth checking out; they could provide you with the inspiration you need to take to the skies.

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A Collective Pitch Quadcopter


Quadcopters aren’t a new thing, but for all the advances in multi-rotor craft, they all still fall into the paradigm of, ‘stick a prop on a motor and repeat three more times. [Curtis Youngblood], one of the top RC heli pilots in the world, came up with a very cool drive system for a quad, requiring only one motor and granting each blade collective pitch that allows for absolutely insane acrobatic ability.

There’s only one motor inside the Stingray 500, as [Curtis] calls his new toy. It’s at the rear of this quad’s H-frame, attached to a shaft running down the spine with a pair of pulleys. All four rotors are driven by this spinning shaft.

Because [Curtis] is an acrobatic pilot, he needed a way to control his ‘copter in more than one direction. To do this, he added four servos on each arm of the quad, giving each rotor collective pitch, just like the tail rotor of a real helicopter. The result is a quadcopter that can fly upside-down with the greatest of ease, perform barrel rolls, and all the other maneuver a true 3D RC ‘copter can do.

The awesome guys at Flite Test had [Curtis] visit their hangar and had him do an awesome demo flight. You can check out that video below.

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Hacking a Cheap Toy Quadcopter to work with Arduino


Building your own quadcopter is an expensive and delicate ordeal. Only after you navigate a slew of different project builds do you feel confident enough to start buying parts, and the investment may not be worth your effort if your goal is to jump right into some hacking. Fortunately, [Dzl] has a shortcut for us; he reverse engineered the communication protocol for a cheap toy quadcopter to work with an Arduino.

The cheap toy in question is this one from Hobbyking, which you can see flying around in their product demonstration video. [Dzl] cracked open the accompanying control handset to discover which transceiver it used, then found the relevant datasheet and worked out all the pin configuration involved in the SPI communication. Flying data is transmitted as 8 byte packets sent every 20 mS, controlling the throttle, yaw, pitch and roll.

[Dzl] took the build a step further, writing an Arduino library (direct Dropbox download link) that should catch you up to speed and allow you to skip straight to the fun part: hacking and experimenting! See his quick video after the break, then convince yourself you need a quadcopter by watching this one save its creator, [Paul], the trouble of walking his son to the bus stop.

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Should all Quadrotors Look like This?

y4 vs quad

In recent years, quadrotors have exploded in popularity. They’ve become cheap, durable, and can do some really impressive things, but are they the most efficient design? The University of Queensland doesn’t think so.

Helicopters are still much more efficient and powerful due to their one big rotor, and with the swashplate mechanism, perhaps even more maneuverable — after all did you see our recent post on collective pitch thrust vectoring? And that was a plane! A few quick searches of helicopter tricks and we think you’ll agree.

The new design, which is tentatively called the Y4, or maybe a “Triquad” is still a quadrotor, but it’s been jumbled up a bit, taking the best of both worlds. It has a main prop with a swashplate mechanism, and three smaller rotors fixed at 45 degree angles, that provide the counter torque — It’s kind of like a helicopter with three tails.

Regarding efficiency, the researchers expect this design could achieve an overall increase of about 25% in performance, compared to that of a standard quadrotor. So, they decided to test it and built a quad and a Y4 as similar as possible — the same size, mass, batteries, arms, and controller board. The results? The Y4 had an increased run time of 15%! They think the design could very well make the 25% mark, because in this test study, the Y4 was designed to meet the specifications of the quad, whereas a more refined Y4 without those limitations could perhaps perform even better.

Unfortunately there’s no video we can find, but if you stick around after the break we have a great diagram of how (and why) this design works!

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