Those of you who have played Call of Duty: Black Ops, will join me in rejoicing the sound of a friendly yelling “UAV online!”, and likewise the sinking feeling you get in your stomach upon hearing the doomsday announcement of”Enemy UAV online!”.
I’ve always had somewhat of a fascination when it comes to anything that flies. I’ve had four model helicopters (I can’t fly any of them particularly well) but for me the joy was in building these things first, or taking them to bits when they (inevitably) crashed.
Multiplex EasyStar - our airframe
So it ought not to come as any surprise then that, while playing Black Ops a few weeks ago, my friend and I had a rare moment of mental synchronicity when we both declared: “let’s build one for real!”, and to hell with the fact neither of us had any real clue where to start. But that’s what teh interwebs are for!
Black Ops aside, there are a few distinct angles to this project which make for a really fun time:
- Building the model: learning how to build a model plane and all necessary mini-skills that go with it
- Hooking up the avionics: speed controllers, batteries and radio
- Adding a micro controller and accompanying sensors for autopilot functionality
- Building a wireless telemetry system and making the “ground station”: mixing physical computing with software systems to build a truly mobile
The plan is to build a radio-controlled model aeroplane that can autonomously navigate several way points and take detailed aerial imagery along the way, purely for recreational purposes. We’ll no doubt figure some way of making some sort of game, too. As a bonus, when we’ve figured out how to do that we’d like to add a live first-person video element to the project so that it’s possible to get a “in cockpit” view in real-time.
As with all crazy ideas, the key to success is planning and there’s been no shortage of that over the Christmas period. The UAV plan will be split into two phases:
- Build an aircraft, learn to fly it manually
- Equip the plane with an autopilot, build the ground station and voila.
Given that neither of us have any fixed-wing flying experience, we figured it necessary to enlist with a local flying club once we’ve built the plane so we learn the basics from the pro’s and join the British Model Flying Association (which also provide insurance!).
After extensive forum research and oogling over product specifications, the final kit list is currently still in development but most of it is currently listed on our Wishpot wishlist. This list gets updated all the time as we substitute parts or buy each item. When the aircraft is finally built I will post the final kit list here.
Airframe and basic electronics
To build a successful aerial imaging platform, the key is having a stable airframe and a large cargo capacity. This therefore requires an aircraft which produces a lot of lift and is built more like a glider than a traditional plane: high-wing designs are in and we’re shooting for reliability over performance.
To this end, we settled on the Multiplex EasyStar Kit which was about £47. The kit includes the basic airframe, a standard motor and all moving parts (prop, servo linkages) but doesn’t include a speed controller, radio TX or RX or any servos.
Following forum advice, we won’t be flying the stock motor or propeller. Instead, we opted for a brushless motor upgrade kit (£79.99) which provides us with an Overlander battery, 30A electronic speed controller and a much more powerful motor with a slightly larger propeller.
For manual flying (and later, switching between manual/autopilot), we opted for a slightly more professional Futaba 6 channel system operating on 2.4GHz. It’s super light weight receiver (9.8 grams) is perfect, and being on the 2.4GHz spectrum means we won’t have to deal with pesky ‘crystals’ or interferrance from other modellers: it’s digital frequency control means our controller will always control our plane.
On board power will be provided by 1 x Overlander Lithium-Polymer 2200mAh 3 cell battery, putting out 11.1V. This will be split between the ESC and the radio gear, though in time we might investigate running the radio off a dedicated smaller battery.
The fun part: telemtry and autopilot
Making anything do anything by itself isn’t exactly easy, especially if you want it to do it well. For the auto pilot, we’ve chosen to use the open-source Ardupilot project which is essentially a set of hardware shields for use with an Arduino, together with some open-source software.
What I’d like to look into doing though is porting the Arduino version of the software to C#, for running on the Netduino (an Arduino ‘clone’ running the .NET Micro Framework).
Essentially, the Ardupilot requires themorpiles and an inertial measurement unit (or, IMU, for short) and a GPS. Data from these sensors can optionally be transmitted via a separate on-board radio system to a ‘ground station’.
Our model’s sensors include:
- XY+Z IR Horizon Sensors
- An EM406 GPS module
- Airspeed sensors
- Barometric pressure sensor
Our telemetry system will beam data back to the ground station via long-range Xbee modules. More precisely, 2 x XBee Pro 50mW modules (Series 2.5 with RPSMA antennas) and a couple of interface boards. These modules have an approximate line-of-sight range of 1 mile in ideal conditions, more than enough for our purposes.
Where are we now?
At this time, the basic airframe has been constructed and most of the equipment needed to build a normal manual flyer aeroplane has arrived and been assembled, with exception to the radio at this point.
Next steps are to complete the installation of the radio and servos, construct the final power distribution harness and then go join the model flying club to learn how to fly. In the mean time, there’ll be some tinkering to do in my spare time to actually construct the Ardupilot autopilot and start adding the sensors. More on that lot to follow in future posts…
Have a great new year!