LED Hack Teaches DJI Mini 2 Drone New Tricks

April 20, 2021 by Tom Nardi 18 Comments

Despite its diminutive proportions, the thrust to weight ratio of the DJI Mini 2 is high enough that it can carry a considerable amount of baggage. So it’s no surprise that there’s a cottage industry of remotely controlled payload releases that can be bolted onto the bottom of this popular quadcopter. But [tterev3] wanted something that would integrate better with DJI’s software instead of relying on a separate transmitter.

As explained in the video below, his solution was to tap into the signals that control the RGB LED on the front of the drone. Since the user can change the color of the LED at any time with the official DJI smartphone application, decoding this signal to determine which color had been selected is like adding several new channels to the transmitter. In this case [tterev3] just needed to decode a single color to use as a “drop” signal, but it’s not hard to imagine how this concept could be expanded to trigger several different actions with a few more lines of code.

[tterev3] wrote some software to decode the 48 bits of data being sent to the LED with a PIC18F26K40 microcontroller, which in turn uses an L9110H H-Bridge to control a tiny gear motor. To get feedback, he’s using a small magnet glued to the release arm and a Hall-effect sensor.

Concerned about how much power he could realistically pull from a connection that was intended for an LED, he gave the release its own battery that is slowly charged while the drone is running. You could argue that since the motor only needs to fire up once to drop the payload, [tterev3] probably could have gotten away with not recharging it at all during the flight. But as with the ability to decode additional color signals, the techniques being demonstrated here hold a lot of promise for future development.

Folks have been strapping additional hardware to commercial quadcopters for years, but modifications like this one that actually let the craft release its payload and fly away hold particular promise for environmental monitoring and building mesh communication networks.

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Micro Quadcopter Designed In OpenSCAD

April 2, 2021 by Lewin Day 20 Comments

Quadcopters are fantastical things, and now come in a huge variety of flavours, from lithe featherweight racers to industrial-grade filming rigs worth tens of thousands of dollars. The Beatle-1 from [masterdezign] comes in at the smaller scale, and its body was created entirely in code.

To create the Beatle-1, [masterdezign] used OpenSCAD, a 3D modelling program that uses code rather than visual tools for producing geometry. Thus, with a series of Boolean operations, extrusions and rotations, a basic lightweight quadcopter frame is created in a handful of lines of text. Then, it’s just a simple job of 3D printing the parts, wiring up four Olimex F1607 motors and hooking up a flight controller and the little drone is ready for takeoff.

The Beatle-1 serves as not only a fun flying toy but also a great example of applying OpenSCAD modelling techniques to real-world applications. Parts are available on Thingiverse for those wishing to roll their own. 3D printed drone frames are popular, and we’ve seen a few around these parts before. Video after the break.

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Resilient AI Drone Packs It All In Under 250 Grams

March 15, 2021 by Tom Nardi 14 Comments

When it was first announced that limits would be placed on recreational RC aircraft heavier than 250 grams, many assumed the new rules meant an end to home built quadcopters. But manufacturers rose to the challenge, and started developing incredibly small and lightweight versions of their hardware. Today, building and flying ultra-lightweight quadcopters with first person view (FPV) cameras has become a dedicated hobby onto itself.

But as impressive as those featherweight flyers might be, the CogniFly Project is really pushing what we thought was possible in this weight class. Designed as a platform for experimenting with artificially intelligent drones, this open source quadcopter is packing a Raspberry Pi Zero and Google’s AIY Vision Kit so it can perform computationally complex tasks such as image recognition while airborne. In case any of those experiments take an unexpected turn, it’s also been enclosed in a unique flexible frame that makes it exceptionally resilient to crash damage. As you can see in the video after the break, even after flying directly into a wall, the CogniFly can continue on its way as if nothing ever happened.

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Lost A Lightweight Quadcopter? Here Are The Best Ways To Find It

March 6, 2021 by Donald Papp 24 Comments

Lost aircraft are harder to find when they are physically small to begin with. Not only are they harder to see, but the smaller units lack features like GPS tracking; it’s not normally possible to add it to a tiny aircraft that can’t handle much more than its own weight in the first place. As a result, little lost quads tend to be trickier to recover in general.

Fluorescent tape adds negligible weight, and will glow brightly at night under a UV light.

The good news is that [Eric Brasseur] has shared some concise tips on how to more easily locate and recover lost aircraft, especially lightweight ones. Recovering aircraft is something every aircraft hobbyist has had to deal with in one way or another, but [Eric] really has gathered an impressive list of tricks and techniques, and some of them go into some really useful additional detail. It occurs to us that a lot of these tips could apply equally well to outdoor robots, or rovers.

Even simple techniques can be refined. For example, using bright colors on an aircraft is an obvious way to increase visibility, but some colors are better choices than others. Bright orange, white, and red are good choices because they are easily detected by the human eye while still being uncommon in nature. Violet, blue, and even cyan on the other hand may seem to be good choices when viewed indoors on a workbench, but if the quad is stuck in dark bushes, those colors will no longer stand out. Another good tip is to consider also adding a few patches of fluorescent tape to the aircraft. If all else fails, return at night with a UV lamp; those patches will glow brightly, and be easily seen from tens of meters.

Some of the tips are used while the device still has power, while others don’t depend on batteries holding out. [Eric] does a great job of summing up those and many more, so take a look. They might come in handy when test flying quadcopters that are little more than an 18650 cell, motors, and a 3D-printable frame.

Attack Of The Flying 18650s

March 3, 2021 by Tom Nardi 31 Comments

When somebody builds a quadcopter with the express purpose of flying it as fast and aggressively as possible, it’s not exactly a surprise when they eventually run it into an immovable object hard enough to break something. In fact, it’s more like a rite of passage. Which is why many serious fliers will have a 3D printer at home to rapidly run off replacement parts.

Avid first person view (FPV) flier [David Cledon] has taken this concept to its ultimate extreme by designing a 3D printable quadcopter that’s little more than an 18650 cell with some motors attached. Since the two-piece frame can be produced on a standard desktop 3D printer in a little over two hours with less than $1 USD of filament, crashes promise to be far less stressful. Spend a few hours during the week printing out frames, and you’ll have plenty to destroy for the weekend.

While [David] says the overall performance of this diminutive quadcopter isn’t exactly stellar, we think the 10 minutes of flight time he’s reporting on a single 18650 battery is more than respectable. While there’s still considerable expense in the radio and video gear, this design looks like it could be an exceptionally affordable way to get into FPV flying.

Of course, the argument could be made that such a wispy quadcopter is more likely to be obliterated on impact than something larger and commercially produced. There’s also a decent amount of close-quarters soldering involved given the cramped nature of the frame. So while the total cost of building one of these birds might be appealing to the newbie, it’s probably a project best left to those who’ve clocked a few hours in on the sticks.

We’ve seen quite a few 3D printed quadcopter frames over the years, but certainly none as elegant as what [David] has created here. It’s an experiment in minimalism that really embraces the possibilities afforded by low-cost desktop 3D printing, and we wouldn’t be surprised to see it become the standard by which future designs are measured.

Demonstrating The Mars Rover Pendulum Problem With A Drone On Earth

February 25, 2021 by Danie Conradie 39 Comments

The sky crane system used on the Perseverance and Curiosity Mars rovers is a challenging control system problem that piqued [Nicholas Rehm]’s curiosity. Constrained to Earth, he decided to investigate the problem using a drone and a rock.

The setup and the tests are simple, but clearly illustrate the problem faced by NASA engineers. [Nicholas] attached a winch mechanism to the bottom of a racing-type quadcopter, and tied a mass to the end of the winch line. At first, he built a foam model of the rover, but it proved to be unstable in the wake of the quadcopter’s propellers, so he used a rock instead. The tests start with the quadcopter taking off with the rock completely retracted, which is then slowly lowered in flight until it reaches the end of the line and drops free. As soon as the rock was lowered, it started swinging like a pendulum, which only got worse as the line got longer. [Nicholas] attempted to reduce the oscillations with manual control inputs, but this only made it worse. The quadcopter is also running [Nicholas]’s own dRehmFlight flight controller that handles stabilization, but it does not account for the swinging mass.

[Nicholas] goes into detail on the dynamics of this system, which is basically a two-body pendulum. The challenges of accurately controlling a two-body pendulum are one of the main reasons the sky crane concept was shelved when first proposed in 1999. Any horizontal movement of either the drone or the rock exerts a force on the other body and will cause a pendulum motion to start, which the control system will not be able to recover from if it does not account for it. The real sky crane probably has some sort of angle sensing on the tether which can be used to compensate for any motion of the suspended rover. Continue reading “Demonstrating The Mars Rover Pendulum Problem With A Drone On Earth” →

Orphaned Gimbal Gets Second Chance To Fly

February 3, 2021 by Tom Nardi 1 Comment

A reality of flying RC aircraft is that at some point, one of your birds is going to fall in the line of duty. It could get lost in the clouds never to be seen again, or perhaps it will become suddenly reacquainted with terra firma. Whatever the reason, your overall enjoyment of the hobby depends greatly on how well you can adapt to the occasional loss.

Based on what we’ve seen so far, we’d say [Rural Flyer] has the right temperament for the job. After losing one of his quadcopters in an unfortunate FPV incident, he decided to repurpose the proprietary gimbal it left behind. If he still had the drone he could have slipped a logic analyzer in between its connection with the motorized camera to sniff out the communication protocol, but since that was no longer an option, he had to get a little creative.

Figuring out the power side of things was easy enough thanks to the silkscreen on the camera’s board, and a common 5 V battery eliminator circuit (BEC) connected to the drone’s 7.4 V battery pack got it online. A cobbled together adapter allowed him to mount it to one of his other quads, but unfortunately the angle wasn’t quite right.

[Rural Flyer] wanted the camera tilted down about 15 degrees, but since he didn’t know how to talk to it, he employed a clever brute force solution. After identifying the accelerometer board responsible for determining the camera’s position, he use a glob of hot glue to push the sensor off of the horizontal. Providing this physical offset to the sensor data caused the camera to automatically move itself to exactly where he wanted it.

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