wcUAVc entry: progress & test flight
I entered an R&D competition as I thought it would be an interesting challenge. This is an update on my progress.
In November 2013 I stumbled on the Wildlife Conservation UAV Challenge. The aim of the competition is to encourage teams from around the world to develop an unmanned aerial vehicle (UAV) that could be used in the national parks of South Africa. The rangers in these national parks struggle to prevent poaching and would benefit enormously from having an ‘eye in the sky.’ I love the idea of using technology to help solve critical problems so I entered the competition (just a few minutes before the deadline). I was the 100th team to enter.
At the time, I wrote up my strategy for entering here.
I decided early on that a fixed-wing (ie. aeroplane) design would be more appropriate than a multi-rotor (ie. quadcopter) as they can cover long distances more easily.
Building and flying a large fixed-wing UAV from scratch is no mean feat. I built some model planes with my brother when we were young and I’ve wielded a soldering iron before but this is my most ambitious project yet.
In order to build up to flying a large UAV with an autopilot module and various sensors, I thought it would be best to tackle the challenge in stages. Firstly, I would learn to fly a remote-controlled trainer plane. Secondly, once comfortable with that, I would learn to fly a slightly larger plane with more advanced technology such as an autopilot module and a camera. The next stage would be a basic build of the Skywalker X8 model that I chose for our competition entry. This would consist only of the basic flying apparatus without an autopilot module or any sensors. Only after all of this would I fly the complete system with a camera and any other required sensors.
The first thing to buy was a remote controlled trainer plane. My research revealed the Hobbyzone Duet, which seemed an appropriate starting point. The Duet is a three channel setup with variable thurst to each prop and an elevator. Thrust is controlled by the left hand stick on the controller, pitch and yaw with the right hand stick. The Duet comes ready to fly with AA batteries for the controller and a charger for the plane battery handily built in to the controller.
The Duet is light and not very powerful. This makes it perfect for beginners, however it also means it is best flown on still days. That said, flying with a gentle breeze begins to prepare you for how a larger plane might handle in the wind.
Once confident flying the Duet, I moved on to a Hubsan Spyhawk.
The Spyhawk is a four channel RC plane with ailerons, elevator and a rudder to control yaw. To begin with I didn’t use the rudder at all and only started to do so as I got more confident. The Spyhawk also has an internal flight controller, providing auto-stabilisation, and a camera that streams video back to a small screen on the transmitter.
My first few flights with the Spyhawk were … bumpy. Figuring out the ideal combination of thrust and elevator to launch with cost me some chunks of the foam fuselage and eventually the camera module too. Now however, my confidence flying the Spyhawk has increased and my landings are much less destructive.
There are many things that flying the Spyhawk taught me but the most important is the value of auto-stabilisation. On the Spyhawk, this feature can be turned on and off mid-flight. One still, clear day I flew up to a good altitude and tried turning auto-stabilisation off. In no time the plane was tumbling out of the sky so I flicked it back on! Somehow the auto-stabilisation corrected the plane’s course but with the plane upside down and trying to correct this led to yet another crash. This particular flight helped me realise that flying entirely under manual control is tricky and an auto-stabilise function would be vital for the X8 build from the outset.
The X8 build
With some flying experience under my belt, it was time to start building the Skywalker X8 model that I had chosen for the wcUAVc entry. I ordered the airframe from China and set about figuring out what electronics were required. I used Steffan Gofferje’s helpful X8 setups page to come up with a suitable starting point.
I am lucky to have some UAV-building friends, one of whom loaned me some key parts such as servos, radio transmitter/receiver and batteries (thanks Andy!). This just left a motor, propeller, UBEC and a flight controller. For a flight controller I chose the open-source APM2.6 as it seems like a popular choice.
After ordering these parts, a small hiccup emerged: the shaft of the motor was on the wrong side relative to the motor mount. Luckily some googling and reading old threads on rcgroups.com revealed that the shaft can be removed, modified and then replaced the right way round. After a session with some borrowed power tools (thanks Alfred!) this was also done.
With the help of velcro, glue, a soldering iron and a scalpel all of the electronic components were now fitted into the fuselage.
The next thing to consider was ground testing. Both moving the sticks and the auto-stabilise function of the flight controller should have the desired effect on the two ailerons. The X8 being a flying wing requires a slightly different setup to normal RC planes as the two servos must work in synchrony when activated by the elevator channel and work against each other when activated by the roll channel. This configuration is required both on the controller unit and in the flight controller. Once done, the ground tests can be run to ensure the transmitter and the flight controller both move the ailerons in the required directions when moving the sticks or tilting the plane.
A few weeks ago I was staying with friends in rural Devon and had finally run out of excuses not to send the Skywalker into the sky. The morning of the test flight was overcast with a light breeze. The field we were using had a gentle downward slope. I had two trusty assistants to help me with launching and filming. Batteries were installed and connected. Final ground tests were done to double check aileron movements and then it was time…
I was almost certain that our first test flight would end up in a crash of some kind — most likely on either take-off or landing. The plan was for me to hand launch the plane, immediately engage the propeller, fly a circuit and then bring it in to land.
With my heart in my mouth, I took the Skywalker and tossed it gently into the breeze. The wind immediately got underneath it and it pitched up. I gave it the beans and pushed the elevator stick forward to try and bring the nose down. Unfortunately the trim wasn’t quite right and pushing the elevator stick forward wasn’t enough to bring the nose down! The plane climbed and climbed before doing a backflip and then entering a flat spin. A flat spin turned out to be a miraculous outcome as the plane landed softly not far from the take-off site. At last, we had our first flight under our belts!
We adjusted the trim, checked the electronics, re-ran the ground tests and then it was time to fly again.
My friend launched it more smoothly this time although there was a brief period of the nose going rapidly up and down until it levelled out. I then banked left and brought it round in a wide arc. At this moment however, the maximum roll limit of the flight controller kicked in preventing a tighter turn. As the angle of the turn was so wide, the plane went out of radio range and came down in the next field. Remarkably it was still in one piece although it did require some repairs to the wing mounts, motor mounts and internal circuitry from the impact of the landing.
There are minor repairs to make to the plane and a longer range radio transmitter/receiver combination to choose. There also needs to be some tweaking to the flight modes so that auto-stabilise allows a greater roll angle and can be switched on and off in-flight. With these adjustments made it will then be time for another test flight.
Once I have flown missions under manual control and using the autopilot module, then I can start to add extra sensors. First up will be a camera with a video transmitter and, in due course, a gimbal to help stabilise the image.
If this project could help you with estate security or if you’d like to help in any way then please get in touch.
Onwards and upwards!