Controlling A Quadcopter With One Dead Motor

January 28, 2021 by Danie Conradie 17 Comments

Quadcopters have incredible flying abilities, but if one loses just a single motor, it drops like a rock. Researchers from the University of Zurich’s Robotics and Perception Group have proven that this does not need to be the case by keeping a quadcopter flying with only three motors.

A quadcopter usually has enough thrust to stay aloft with only three motors, but it will spin uncontrollably in the yaw axis. It is impossible to stop a quadcopter from spinning, so the focus for researchers was on keeping the drone controllable while it’s spinning. To achieve this, accurate position and motion estimation is required, so they attached a pair of cameras to the bottom of the craft for visual-inertial odometry (VIO). One is a normal optical camera, while the other is an event camera, which has pixels that can independently respond to changes in light as they occur. This means that it has better low light performance and does not suffer from motion blur.

The feeds from the cameras are analyzed in real-time by an onboard Nvidia Jetson TX2 for state estimation, which is then used with an optical range sensor and onboard IMU to maintain controlled flight, as demonstrated in the video after the break. The research paper is free to read, and all the code is available on GitHub.

New developments in drone control schemes are always fascinating, like this hexacopter with an innovative motor layout to achieve six degrees of freedom, or a conventional helicopter with a virtual swash plate.
Continue reading “Controlling A Quadcopter With One Dead Motor” →

How To Run Alternative Batteries On The DJI Mavic Mini

January 25, 2021 by Lewin Day 40 Comments

Rechargeable batteries are ubiquitous these days, freeing us from the expense and hassle of using disposable cells. However, this has come with the caveat that many manufacturers demand their equipment only be used with their own official batteries. [aeropic] wasn’t a fan of this, so built a circuit to allow his DJI Mavic Mini to fly with any batteries he pleased.

The Mavic Mini uses I2C to communicate with official packs, making the hack relatively straightforward. [aeropic] built a board nicknamed B0B, which tells the drone what it wants to hear and lets it boot up with unofficial batteries installed. The circuit uses a PIC12F1840 to speak to the drone, including reporting voltage on the cells installed. Notably, it only monitors the whole pack, before dividing the voltage to represent the value of individual cells, but it shouldn’t be a major problem in typical use. Combined with a few 3D printed components to hold everything together, it allows you to build your own cheap pack for the Mavic Mini with little more than a PCB and a few 18650 cells.

It’s always good to see hackers getting out and doing the bread and butter work to get around restrictive factory DRM measures, whether its on music, printer cartridges, or drone batteries. We’ve even seen the scourge appear on litter boxes, too. Video after the break.

Continue reading “How To Run Alternative Batteries On The DJI Mavic Mini” →

ExpressLRS: Open Source, Low Latency, Long Range RC Protocol

January 19, 2021 by Danie Conradie 42 Comments

One of the major choices a newcomer to the RC flying hobby must make is on the RC link protocol. To add the list of choices (or confusion) there is now a new open-source, low latency, and long-range protocol named ExpressLRS.

ExpressLRS’s claim to fame is high packet rates of up to 500 Hz, with plans for 1000 Hz, and latency as low as 5 ms. Long-range testing has pushed it out to 30 km with a flying wing (video below), but this is not unheard of for other protocols. Most modern RC protocols run either in the 2.4 GHz or 915/868 MHz bands, with the latter having a definite advantage in terms of range.

ExpressLRS has options to run on either band, using Semtech SX127x (915/868 MHz) or SX1280 (2.4 GHz) LoRa transceivers, connected to STM32, ESP32, or ESP8285 microcontrollers. The ESP microcontrollers also allow software updates over Wi-Fi.

We’re excited to see an open-source competitor to the proprietary protocols currently dominating the market, but several open-source protocols have come and gone over the years. Hardware availability and compatibility is a deciding factor for a new protocol’s success, and ExpressLRS already has an advantage in this regard. Existing Frsky R9 transmitters and receivers, and Immersion RC Ghost receivers are compatible with the firmware. There are also DIY options available, and the GitHub page claims that several manufacturers are working on official ExpressLRS hardware.

If you’re already into the RC hobby, and you have compatible hardware lying around, be sure to give it a try and give some feedback to the developers! One scenario we would like to see tested is high interference and congested band conditions, like at RC flying events.

All the source code and hardware designs are available on GitHub, and there are active community discussions on Discord. Continue reading “ExpressLRS: Open Source, Low Latency, Long Range RC Protocol” →

Mavic Mini Gets Custom Clear Case

January 19, 2021 by Lewin Day 4 Comments

Apparently, in the drone scene, sticker wraps are popular for a custom aesthetic. [Useless Mod] wanted to go a little further, however, and decided to build a full crystal enclosure for his Mavic Mini, facing some hurdles along the way. (Video, embedded below.)

The first stage of the build was disassembly, with the compact 249 gram drone requiring a deft touch to avoid damaging the delicate ribbon cables and mechanisms inside. With the drone stripped down to its bare components, a silicone mould was made of each individual piece of the case, with new parts being cast in clear epoxy. It’s not a job for the faint of heart, with many undercuts and complex features to contend with. However, [Useless Mod] managed to produce the parts and get it all back together.

An initial test flight ended poorly, when the drone entered an uncontrollable wobble due to the case not being fully assembled. However, with fresh internals and with everything properly put together, everything worked! It’s not a build we’d suggest for the inexperienced, as the moulds required are complex and the electronics quite fragile. The final result is a good one though, and it even weighs 10 grams less than the original casing!

For those in the US, the world of drones is set to change drastically in short order.

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Six Degrees Of Freedom Omnicopter With Ardupilot

January 9, 2021 by Danie Conradie 12 Comments

Modern multirotors are very maneuverable but are mostly limited to hovering in a single orientation. [Peter Hall] has gotten around this by building an omnicopter drone with six motors mounted in different orientations on a collapsed tetrahedron frame.

The shape of the frame consists of six tetrahedrons all joined together at a single point. With a motor in each frame, the drone can produce a thrust vector in any direction, to achieve six degrees of freedom. The control system is the challenging part of this project, but fortunately [Peter] is one of the Ardupilot developers. Unlike a standard multirotor, it doesn’t need to tilt to move around laterally but can keep its orientation constant. One of the limiting factors is that the motors need to stop and reverse rotation for direction changes, which takes time. At slow maneuvering speeds this isn’t a major problem, but at higher speeds rotation is noticeably less smooth.

Because the drone is symmetrical all around, keeping track of orientation is challenging for a human pilot, but it’s perfect for an autopilot system like Ardupilot. In the video after the break, [Peter] demonstrates this by flying the drone around while the autopilot rotates it randomly. The 6DoF control system is open source and a pull request is live to integrate it into the official version of Ardupilot. The obvious application for this sort of drone is for inspection in and around structures.

This omnicopter is an entry into the Lynchpin drone competition by the celebrity [Terrence Howard]. We’re not quite following his claims regarding the scientific significance of this shape, which he named the “Lynchpin”, but it works for drones. Continue reading “Six Degrees Of Freedom Omnicopter With Ardupilot” →

Transforming Drone Can Be A Square Or A Dragon

January 1, 2021 by Danie Conradie 8 Comments

When flying drones in and around structures, the size of the drone is generally limited by the openings you want to fit through. Researchers at the University of Tokyo got around this problem by using an articulating structure for the drone frame, allowing the drone to transform from a large square to a narrow, elongated form to fit through smaller gaps.

The drone is called DRAGON, which is somehow an acronym for the tongue twisting description “Dual-Rotor Embedded Multilink Robot with the Ability of Multi-Degree-of-Freedom Aerial Transformation“. The drone consists of four segments, with a 2-DOF actuated joint between each segment. A pair of ducted fan motors are attached to the middle of each segment with a 2-DOF gimbal that allows it to direct thrust in any direction relative to the segment. For normal flight the segments would be arranged in the square shape, with minimal movement between the segments. When a small gap is encountered, as demonstrated in the video after the break, the segments rearrange into a dragon-like shape, that can pass through a gap in any plane.

Each segment has its own power source and controller, and the control software required to make everything work together is rather complex. The full research paper is unfortunately behind a paywall. The small diameter of the propellers, and all the added components would be a severe limiting factor in terms of lifting capacity and flight time, but the concept is to definitely interesting.

The idea of shape shifting robots has been around for a while, and can become even more interesting when the different segment can detach and reattach themselves to become modular robots. The 2016 Hackaday Grand Prize winner DTTO is a perfect example of this, although it did lack the ability to fly. Continue reading “Transforming Drone Can Be A Square Or A Dragon” →

Federal Aviation Administration Announces Major Drone Rule Changes

December 29, 2020 by Dan Maloney 61 Comments

If new rules from the FAA regarding unmanned aircraft operations in the US are any indication, drones are becoming less of a niche hobby and more integrated into everyday life. Of course, the devil is in the details, and what the Federal Aviation Administration appears to give with one hand, it takes away with the other.

The rule changes, announced on December 28, are billed as “advanc[ing] safety and innovation” of the drone industry in the United States. The exciting part, and the aspect that garnered the most attention with headline writers, is the relaxation of rules against night operation and operating above people and moving vehicles. Since 2016, it has been against FAA regulations to operate drones less than 55 pounds (25 kg) at night or over people without a waiver. This rule can be seen as stifling innovations in drone delivery, since any useful delivery service will likely need to overfly populated areas and roadways and probably do so at night. The new rules allow these operations without a waiver for four categories of drones, classified by how much damage they would do if they were to lose control and hit someone. The rules also define the inspection and certification regimes for both aircraft and pilot, as well as stipulating that operators have to have their certificate and ID on their person while flying.

While this seems like great news, the flip side of the coin is perhaps less shiny. The rule changes also impose the requirement for “Remote ID” (PDF link), which is said to be “a major step toward full integration of drones into the national airspace system.” Certain drones will be required to carry a system that transmits identification messages directly from the aircraft, including such data as serial number, location and speed of the drone, as well as the location of the operator. The rules speculate that this would likely be done over WiFi or Bluetooth, and would need to be receivable with personal wireless devices. The exact technical implementation of these rules is left as an exercise to manufacturers, who have 30 months from the time the rules go into effect in January to design systems, submit them for certification, and get them built into their aircraft. Drone operators have an additional year to actually start using the Remote ID drones.

For the drone community, these rule changes seem like a mixed bag. To be fair, it’s not exactly unexpected that drones would be radio tagged like this, and the lead time allowed by the FAA for compliance on Remote ID seems generous. The ability to operate in riskier environments will no doubt be welcomed by commercial drone operators. So who knows — maybe the rules will do what they say they will, and this will stimulate a little innovation in the industry. If so, it could make this whole thing a net positive.