Build your own computer-stabilized flying UAV/RPV drone platform

What distinguishes a radio-controlled  aircraft from an Unmanned Aerial Vehicle (or “drone”) is the presence of an on-board computer (the Auto-Pilot Module, or APM) capable of flying the vehicle with or without direct control of a person.

With Telemetry, but before adding platform sensors (video/still cameras, ultrasonic range-finders, etc)

I’ve been following and building DIYDrones.com autopilot systems since 2009, and they have come a long way!   With the new multi-copter kits in their store,  3D Robotics makes this drone technology really accessible.    Chris Anderson (founder of DIYDrones, CEO of 3D Robotics, and former Editor in Chief of Wired Magazine) has turned his focus to “amateur” drone development, and the effort really shows.

Since our government essentially allows no commercial use of UAV’s in the National Air Space (NAS), the only “approved” uses are for personal and non-commercial applications (hopefully this will change in the next few years).   Since I work with emergency service groups,  my application areas of interest are wildfires, flooding, and search & rescue.   In other countries, UAV’s are involved with a wide range of creative uses, including food & supply deliveries or delivering papers.

One of the amazing things about the DIYDrones projects is that the hardware & software is “open source“.  This means that all the circuit boards, diagrams, layouts, and programs are available to anyone in a form such that they can be copied and/or modified freely.   The usual caveat is that if you modify anything and use it for commercial purposes, those changes must be made available to anyone who asks.   All the resources are just a “google” away; even the development environments & tools used to make the software are open-source (how’s that for “bootstrapping“?).

Note: The main purpose of this post is to pull together disparate links & references into a linear form that can be easily followed (along with my experiences).  This is not a complete step-by-step tutorial; researching the embedded links and documents should fill in most of the gaps.

The hexacopter kit (one of several Arducopter products) provides a stable platform for flying a wide variety of sensors, telemetry, and imaging devices.  The basic auto-pilot module (APM 2.5+) combines GPS (position), magnetometer (directionality),  inertial measurement units (stability, position),  barometric pressure (altitude), and power sensors (an amazing amount of functionality for the price).  I chose the hexacopter over the quadcopter simply for additional payload capacity.

The basic components are the flying platform (‘copter, plane), ground control station (GC or GCS), and radio interfaces (control & telemetry).   A fun way to get an overview of how everything goes together (and what NOT to-do) is to read through the DIYDrones blog posts;  it took me a few days.    It’s a good way to spend your time while your waiting for your parts to arrive 😉

Hexacopter parts

With that said, let’s dive in-to what the raw costs are to build a hexacopter with video downlink, telemetry, auto take-off & landing sensor, ground station, batteries, charger, and radio:

Basic Parts Only (shipping & taxes not included):
———–
$570  – Hexacopter basic parts, ublox GPS & APM 2.5+ 850KV motors and 10×4.7 props.
$425  – Spektrum DX7s/DX8 with receiver
$100  – (2) Spare Motors, (2) motor shells, (2) spare ESCs, (3) additional sets of props
$20   – Receiver => APM cabling
$1000 – Laptop ground station/mission planner (estimated)
$170  – Copy of windows 7 (retail) to run on laptop (if not included w/laptop)
$125  – LiPoly Charger & battery(s)
———–
$2410.00

Optional Parts:
——————–
$40   – Ultrasonic ground sensor
$100  – Telemetry & APM cable
$270  – Hi-res video camera (not hi-def), lenses + Roll/Tilt mount & servos
$250  – Video (downlink) transmitter, receivers, and patch antenna
$200  – Diversity Receiver
$90   – Readymaderc(.com) pan/tilt antenna tracker
$350  – Video Goggles
————
$1300.00

Of course, your mileage may vary (YMMV) if you have some of these parts on-hand, or can acquire them used.

If you’re still with me, let’s look around the ‘verse to start building a vocabulary.   Starting with the Newbie’s guide to UAV’s to get a quick grasp of what’s this stuff all about.   Then be sure to read the DIYDrones site rules to know what’s expected of you.  Another quick overview page can be found here as well as here.

On the kit purchase page (hexacopter), you’ll find links to the assembly instructions and other places of interest (forum, development wiki, etc).   Another site that I found useful for assembly instructions is arducopter.co.uk.

As I mentioned above, you might consider ordering a couple of extra motors and a set of propellers.  These are the things most likely to be damaged in an “excursion”.  Motor shells are also handy to have around since they are an integral part of the propeller shaft.

Be sure to visit the “get it” page, which has useful purchase information along with links to radio gear, batteries, chargers, etc.   Being an electric r/c enthusiast, there’s a lot of assumed, but unmentioned familiarity with the technologies.  For example, care & feeding of Lithium-Polymer batteries/chargers (lots of great fire videos on-line; Boeing was recently bit by problems in their 787 using similar batteries), 2.4Ghz radios, ESCs, motors, etc.    A great site for lots of background & info is RCHelicopterFun.com.  I have several of his books covering traditional helicopter set-up and maintenance (BTW, this same APM hardware can be used to run traditional helicopters too – check this out).

When you place your order, be sure to also buy male-male 10cm servo lead wires to connect your receiver to the APM.  I found a good place on ebay (10 for $11, free shipping from USA).

Once your kit arrives, be sure to check your parts; the metric bolts (especially nylon) can be hard to find locally, so be sure you have them all.    The folks at DIYDrones support have been very helpful.   Also, before you install the power distribution board in the frame, it’s much easier to install the battery straps first (trust me ;-).

Before hooking up ESCs

As you’re building the frame (and after putting the connectors on the ESC’s), it’s a good idea to check your ESC’s and motors before you mount them (and after).  I had a couple of motors that I felt were too bad to fly for either vibration or bearing noise issues.   Power them up using a servo tester, or with your receiver & transmitter.   After mounting the motors, test them again for vibration & noise. Before strapping your ESC’s in, it’s a good idea to get the motor rotation correct.  Remember, different propellers are needed for different motor rotations (so they all ‘blow’ down).  Just exchange any two of the three motor wires to reverse motor direction.

Important:  Wherever you have metal-to-metal bolt/nut connections, be sure to use some form of thread-locker to keep them from vibrating loose (struts, motors, ..).  I use “blue” Locktite 242.  Nothing quite makes your day like watching a motor fly off on its own (along with the subsequent vehicle “excursion”).   Likewise be sure your propellers are always secure.

Now that your frame is complete, let’s move into the “quick start guide“.  In step one, download and install the ground station/mission planner software.  The ground station software is also used to load your APM with the current firmware (assuming an Internet connection).  NOTE: You cannot use the USB connection and have the telemetry module connected at the same time; they share the same interface, so unplug the telemetry module, if installed.  For me, it took several attempts at uploading the firmware before it loaded and verified successfully (YMMV).  After uploading new firmware, it’s recommended going into the command line interpreter, issuing the “setup” command, then typing the commands: “flash”, and “reset”; this flushes out any old/stale parameter settings.

A good site for instructions on hooking up your APM power module is here.  This will enable your telemetry module to relay battery voltage to the ground station.

Since you’ve already built the frame (step 2), move on-to step 3, and connect your receiver to the APM 2.   Referencing your frame assembly instructions,  mark the motor booms as 1-6 indicated in the instructions, and connect the 6-pin connector from the power module to the 1-6 outputs of the APM.   Since the APM and power module share ground & power, only a single wire/ESC is needed to be connected to the APM.  DO NOT put propellers on at this time!

Continue to follow the quick-start steps 4-7, up to the point of flying.   I had to reverse several controls on my transmitter to match what the APM needed (how you do this will vary with transmitter type).

When I attempted auto-calibration of the ESCs, there was one that just kept beeping, and wouldn’t calibrate. So I lowered my throttle trim by “6 clicks”; then when I recalibrated, all went smoothly.   Apparently all the speed controllers are not created equal, and are subject to temperature tantrums (since they are not crystal-stabilized).  Here’s a link to the ESC manual.    There are better motor controllers out there, some of which are crystal-stabilized (temperature invariant), and with faster-response firmware (A.K.A Simon K) for similar prices.  Not using crystal-stabilized speed controllers means you’ll need to re-calibrate the ESCs when the temperature changes “too-much” (whatever that means to your ESCs).   Check out this site as-well for more information on the Simon K firmware & flashing).

Adding telemetry is covered here.  The clear plastic sheath which comes with the transmitter and receiver boards is heat-shrink.   Just be careful when soldering the right-angle pins on the ground-station side circuit board, and then also when connecting the 6-pin connector.    How-to set-up your ultrasonic range-finder  can be found here; for automatic take-off, landings & terrain following.

Flyable configuration before adding telemetry

Notice the vibration dampening foam under the GPS and APM module.  These units are sensitive and should be cushioned.   To minimize vibration, also balance your propellers! Testing your motors/direction (and other things) can be done through the command line interface, as discussed here.  The motor-test firmware I was using (2.9.1) didn’t behave the way as described; the firmware just spun each motor (1-6 in-order) for a second, so that direction and placement could be verified.

Note:  When reconfiguring the APM, shifting it, changing padding, etc, the accelerometers must be recalibrated!  Click on “configuration tab” in the mission planner (with USB cable connected interfaced to the APM), and on the left side, select “arducopter level”, then press “Calibrate Accel” & follow the directions.

The basic platform (no telemetry or sensors) weighs in at 3.4 pounds with a 3S-2200mAh battery.   This battery yields 4 minutes of flight time on the hexacopter, while the same battery allows 8 minutes of flight-time on my TREX-450.   A 3S-4000mAh battery lets me fly for 8 minutes; with lots of lifting power for larger battery packs (over two pounds).

The platform flies amazingly well.  My DX7 receiver has a 3-position flight mode switch, which I programmed during set-up for “stabilized flight”, “loiter”, and “return to landing location”.   I have yet to add more flight modes by using another channel switch (giving 6 modes).    It’s fun & easy to just push the platform around in stabilized mode;  it’s responsive and VERY stable.    Clicking over to loiter, the craft just hangs in the air, no hands on the controls are needed. The APM has lots of features, including data logging (as does the ground station) to help you figure out what happened when things go wrong.   I may cover this in a future post, but for the moment, I leave it as an exercise for the reader.

Check the forums or tech support pages for help; lots of questions can be answered from there.

As always, safety first; this baby is a flying Cuisinart(tm) so be careful (no bench testing with propellers)!   I also recommend joining the AMA, if you haven’t already; they lobby our government for personal/private use in the NAS.   They also have published, government approved, guidelines for flying these platforms.  Another organization lobbying for commercial use of UAV’s is the AUVSI.  They have chapters and events around the country.   Finally, I can’t end without a plug for the ARRL and amateur radio.  As you investigate radio & video systems, many come with the caveat that you must have an amateur radio license for legal operation.   This is due to the power output of some of these systems; they exceed FCC license-free use.  The ARRL is constantly working with the FCC to keep wireless spectrum open for personal/private use.  I can’t help but feel that without them, we wouldn’t have the (spectrum) freedoms we enjoy today.

UPDATES:
Here’s an inexpensive & neat set of landing-gear upgrades.
Ultrasonic sensors don’t apparently work well below 50F; keep them warm!
Throttle failsafe in-action.