The flight controller is the nerve center of a drone. Drone flight control systems are many and varied. From GPS enabled autopilot systems flown via two way telemetry links to basic stabilization systems using hobby grade radio control hardware, there is an open source project for you.
Modern drone flight controllers can trace their roots back to R/C helicopters. Historically, R/C planes were controlled directly by the pilot’s radio. Helicopters added a new wrinkle to the mix: tail rotors. Helicopters use their tail (or anti-torque) rotor to counteract the torque of the main rotor attempting to spin the entire helicopter’s body. It all works great when the helicopter is hovering, but what about when the pilot throttles up to fly out? As the pilot throttles up, the torque increases, which causes the entire helicopter to do a pirouette or two, until the torque levels out again. The effect has caused more than one beginner pilot to come nose to nose with their R/C heli.
The solution to this problem was gyroscopes, heavy brass spinning weights that tilted in response to the helicopter’s motion. A hall effect sensor would detect that tilt and command the tail rotor to counteract the helicopter’s rotation. As the years wore on, mechanical gyros were replaced by solid state MEMS gyros. Microcontrollers entered the picture and brought with them advanced processing techniques. Heading hold gyros were then introduced. Whereas older “rate only” gyros would drift, weathervane, and wiggle, heading hold gyros would lock down the helicopter’s nose until the pilot commanded a turn. These single axis flight controllers were quickly adopted by the R/C helicopter community.
Today’s flight control systems have many sensors available to them – GPS, barometric pressure sensors, airspeed sensors, the list goes on. The major contributors to the flight calculations are still the gyros, coupled with accelerometers. As the name implies, accelerometers measure acceleration – be it due to gravity, a high G turn, or stopping force. Accelerometers aren’t enough though – An accelerometer in free fall will measure 0 G’s. Turning forces will confuse a system trying to operate solely on accelerometer data. That’s where gyros come in. Gyros measure rate of rotation about an axis. Just as our helicopter example above covered yaw, gyros can be used to measure pitch and roll of an aircraft. A great comparison of gyros and accelerometers is presented in this video from InvenSense.
Stay with us after the break for a tour of available flight controllers and what each adds to the mix. Continue reading “Droning On: Choosing a Flight Controller”
In the world of drones, quadcopters, and unmanned aerial vehicles, the community has pretty much settled on AVR microcontrollers for the low end, and ARM for the high performance boards. If the FAA doesn’t screw things up, there will soon be another market that requires even more computational power, and Navio, the autopilot shield for the Pi, is just the thing for it.
Where high end multicopter and autopilot boards like the OpenPilot Revolution use ARM micros, there’s a small but demanding segment of the hobby that needs even more processing power. Think of something like the Outback Challenge, where fixed-wing drones search the desert for a lost mannequin autonomously. You’re going to need OpenCV for that, and that means Linux.
Navio is a shield for the Raspberry Pi, complete with a barometric pressure sensor, gyros, accelerometer, and compass, and GPS. It’s designed to run a more real-time version of Linux, and has the ability to do some interesting telemetry configurations – putting a 3G modem on the Navio isn’t much of a problem, and since it’s a Raspi, doing image processing of a downward facing camera is just a matter of writing the code.
The Navio team is currently running an Indiegogo campaign, with the baseline version available for $145. That’s pretty close to the price of the OpenPilot Revolution. There’s also a version upgraded with the U-blox NEO-6T that allows for on-board processing of raw GPS data.
[AwesomeAwesomeness] wanted a low cost quadcopter, so he built one from scratch. Okay, not quite from scratch. [AA’s] cookie mix came in the form of an Arduino Uno and some motors. He started with motors and propellers from a Hubsan X4 quadcopter. Once the power system was specified, [AA] designed a frame, arms, and motor pods in Solidworks. He printed his parts out and had a sweet quadcopter that just needed a brain.
Rather than buy a pre-made control board, [AA] started with an Arduino Uno. An Arduino alone can’t source enough current to drive the Hubsan motors. To handle this, [AA] added a ULN2003A Darlington transistor array. The 2003A did work, but [AA] had some glitching issues. We think FETs would do much better in this application, especially when running PWM.
On the control side of things, [AA] added an MPU-6050 Triple Axis Accelerometer and Gyro breakout from SparkFun. The 6050 has 3 gyros and 3 accelerometers in one package. Plenty for a quadcopter.
All this left was the coding. Multicopters generally use Proportional-Integral-Derivative (PID) control loops to maintain stability in the air. [AA] used the Arduino PID library for his quadcopter. He actually created two PID instances – one for pitch and one for roll.
[AA] doesn’t have any videos of his quadcopter in action yet, and we’re guessing this is due in part to weight. Lifting an Uno, a perfboard, and a frame is a tall task for those motors. Going with a one of the many tiny Arduino’s out there would help reduce weight. In addition, [AA] could use a gear system similar to what is used in the Syma X series quadcopters. Stick with it – you’re on the right track!
[Eric] has figured out a great way to build quadcopters out of recycled computer motherboards. Multicopters come in all shapes and sizes these days. As we mentioned in the last issue of Droning On, they can be bought or built-in a multitude of materials as well. Drones have been built using materials as varied as wood, PVC pipe, carbon fiber, and aluminum.
One of the more common commercial materials is G10 fiberglass sheet. It’s stiff, strong, and relatively light. Printed circuit boards are generally made of FR-4 fiberglass, G10’s flame resistant cousin. It’s no wonder [Eric] had quadcopters in his eyes when he saw a pile of motherboards being thrown out at his university.
[Eric] used a heat gun and a lot of patience to get all the components off the motherboard. With a bit of care, most of the components can be saved for future hardware hacks. This is one step that’s best performed outside. Hot melting plastics, metals, and resin fumes aren’t the greatest things to inhale.
Clean PCBs in hand, [Eric] headed to his local TechShop. He drew his dead cat style frame in SolidWorks and cut it out on a ShopBot. While a high-end CNC cutter is nice, it’s not absolutely necessary. The fiberglass sheets could be cut with a rotary tool or a jigsaw. No matter how you cut it, be sure to wear a mask rated for fiberglass resins and some protective clothing. Fiberglass plate is nasty stuff to cut.
Once the upper and lower frame plates were cut, [Eric] completed his quad frame with some square wooden stock for arms. The final quad is a great flier, and spare parts are easy to source. Nice work on the recycling, [Eric]!
Continue reading “Quadcopter Built From Recycled Motherboards”
Long range wireless control of a project is always a challenge. [Mike] and his team were looking to extend the range of their current RC setup for a UAV project, and decided on a pair of Arduino mini’s and somewhat expensive Digi Xtend 900Mhz modems to do the trick. With a range of 40 miles, the 1 watt transceivers provide fantastic range. And paired with the all too familiar Arduino, you’ve got yourself an easy long range link.
[Mike] set the transmitter up so it can plug directly into any RC controller training port, decoding the incoming signal and converting it into a serial data package for transmitting. While they don’t provide the range of other RF transmitters we’ve seen, the 40 mile range of the modem’s are more than enough for most projects, including High Altitude Balloon missions.
The code for the Arduino transmitter and receiver sides is available at their github. Though there is no built-in error correction in the code, they have not had any issues. Unfortunately, a schematic was not provided, but you should be able to get enough information from the images and datasheets to construct a working link.
The advancement of Quadcopters and their capabilities over the last few years has been amazing. Unfortunately, the price point to get into the sport with a decent size, non-toy, vehicle is still several hundred dollars. And what’s the fun with buying one when you can built it?!? Strapped for cash and feeling the same way, [Hans] over at the hackerspace Knackatory decided to build a quadcopter from e-waste.
The + shaped frame is made from lightweight plywood. It’s pretty obvious that the main rotors are PC Fans, 140mm in this case. Normally, these wouldn’t be able to create enough lift to get out of their own way except the on-board 24v Dewalt cordless tool battery bumps up the fan speed to 15,000 rpm. The one orange fan allows the operator to maintain a visual reference to which side of the ‘copter is forward.
Continue reading “E-Waste Quadcopter Lifts Your Spirits While Keeping Costs Down”
Sure there are reward posters for missing cats, dogs, and other various pets — but now in Denver, a man named [Merrick] makes a plea for his $2400 missing drone.
We couldn’t help but chuckle at this news story because it could be the tip of the iceberg. As drones become more and more common place, seeing missing posters for them could become pretty normal! The problem is, when you’re using a long-range drone, and flying it in a city, it is very possible to lose your line of sight and lose the device altogether. That is exactly what happened to poor [Merrick] the other day. Thinking quickly, he started making lost drone posters, and after channel 7 news reported on it, it was discovered in an alleyway the following day. The person who found it thought it was government related and didn’t want to mess around with it — it’s a pretty serious looking drone. Continue reading “Missing Drone Posters Are a Hilarious Look into the Future”