Quadcopter: Radio components

In researching the requirements for a quadcopter I found that I needed a real RC hobby radio.  I’ve looked into these in the past and was always daunted by the price of the radios  used traditionally such as those by Futaba and Airtronics.  But, given that I was going to be really getting into these copters I decided to go ahead and spring for a good one.  I started looking around at what others have used and ran across several.  First, the ones I mentioned are still in use, but they’ve moved away from the 75MHz band and analog signaling they have used for years and instead started using 2.4GHz.  And not just that, they now sport spread spectrum, frequency hopping, and digital signals which all adds up to a highly reliable radio solution with tremendous range.  Even the most basic radios have a range of 1.5Km which I find totally amazing.

With that knowledge in mind, I started looking at the various options. There is a good 8-channel setup from Futaba, and the same from Airtronics. Lots of people like Spektrum and Hitec as well and generally they are pretty similar in terms of feature set. They all come in at about $300 and include features such as multi-model memory, touch-screen displays with telemetry, and SD-card slots. But then I stumbled across what is almost an open source radio.  The Turnigy 9XR is an Arduino-based radio using low-cost parts shared with cell phones that are really inexpensive.  This results in a radio platform that costs $50 and takes a JR-style TX/RX module (those are the pieces that actually do the broadcasting and reception.)  It doesn’t have a touch-screen display, but otherwise it is pretty similar in terms of features as the $300 models.  This is the 3rd generation model and others find it works great.  Given its Arduino roots and the ability to run an open source open9x firmware stack, I decided I had to give it a try. And hey, if it doesn’t work out, I can always switch to another brand and re-use the RX/TX module.

I purchased the Turnigy 9XR from hobbyking.com and the Frsky DJT transmitter and V8FR-II receiver for a total of $90.  I’ll let everybody know how it works.

Photo Quadcopter Project

As I said in my previous post, I’m going to chronicle my quadcopter build.  I’ve never done this before so I expect to make some mistakes.  Hopefully I can learn from others and keep those to a minimum while learning lots of things along the way.

The first quad I’ve decided to build is going to be focused on photography.  I’m looking for still and video pictures taken from the perspective of the quad.  I want to try to keep the weight below 1000g total and I think this will do it.  Here is the quad I’ve designed so far and what I’ve purchased:

Frame: Turnigy Talon v2, Carbon Fiber, 550mm, 280g, $50
Why: I wanted a decent size frame to maximize stability.  I’m not interested in aerobatics with this quad, so a big frame is the way to go.  I also wanted to minimize the weight of the frame.  I’ve read the stories of many others making frames from aluminum, wood, etc. and finding they were just too heavy.  Hopefully this will do the trick.
Where: I purchased this frame from hobbyking because they had a great price for a carbon fiber frame ($50) and because I was ordering some other items from them at the same time.

APM 2.5+ ModuleFlight Controller: ArduPilot Mega 2.5+ with , 21g, $180
Why: Ultimately I want a craft that can handle autonomous flight.  While I’m sure I’ll have fun manually controlling the copter I am most interested in building a drone.  I’m looking for a device that can fly itself and take photos/video.  In Jan 2013, this is the controller to use if you’re interested in that.  While there are other controllers that are cheaper, I don’t think any of them possessed the software and community that this does.  The ArduPilot Mega contains an ATMEGA2560 Arduino Mega.  It also includes a ton of useful modules including a 3-axis gyro, accelerometer, high resolution altimeter, magnetometer (aka digital compass), and an off-board Mediatek GPS.  There is an option to deliver telemetry data via an XBee radio module to a laptop but I didn’t choose to buy that yet. I figure that if I want it later, I can always order it as an add-on ($40).
Where: I ordered this from the source – 3drobotics.com.  There is a way to order it for less if you’re willing to do more work in terms of soldering and buying the connectors yourself – rctimer.com has one for $140.

Flight Controller-add on: LV-MaxSonar-EZ0, 4.3g, $30.
Why: I decided to add on the sonar module after reading about how you can use it to let the craft land itself.  The ArduPilot contains an altimeter that allows it to detect its height, however that device is unusable below 10 feet.  In order to fly and land safely a sonar module is used to get accurate height data and allow ‘nap of the earth’ style flight.  That said, I also read plenty of posts about these things not working right all the time.  It seems the device can be noisy in that its data feed contains some bad data while flying over uneven terrain like grass (versus smooth pavement.)  We’ll see!
Where: I got this when I purchased the flight controller from 3drobotics.com.

Motor: 4 x NTM 28-30A 750kv / 140w, 67g each, $15 each
Why:  I wanted motors that were proven but could be had for a reasonable price.  After the props, these parts are the ones that are most likely to break in a crash.  And while I hope I can keep that to a minimum, I know this is going to crash.  I picked these after reading some people being happy with them and using a tool to determine if 4 750kv motors would provide enough lift.  I want to have room to spare in case I wan to put on a relatively heavy camera.
Where: I ordered these from hobbyking.com while ordering most of the other parts.  Luckily these parts were in the US warehouse in Seattle meaning I could keep the shipping costs down (shipping from China is more expensive than I expected.)  I ordered 6 in order to have a couple as backups.  I also ordered the accessory kit which includes the prop adapter (a collet to hold the propeller in place) and mounting brackets and screws.  I don’t have data on the weight of these parts unfortunately.

Electronic Speed Controller: 4x Turnigy Plush 25A, 22g each, $13 each
Why: An RC aircraft requires a speed controller per motor that allows the flight controller to change the speed of the propeller when it needs to.  The idea is simple, but apparently these little controllers are the source of much frustration.  They can overheat and fail and when they do, a quadcopter is going to crash.  While a fixed wing aircraft can glide down if the speed controller fails, a quadcopter can’t, obviously.  The prevailing wisdom is to place these controllers out on the arm of the quad away from the heat-generating devices like the battery and flight controller.  I see that many people like to ensure they are being hit by the propwash in order to cool them.  There is one interesting feature to these little controllers I didn’t expect, and that is because of what they do already they include a regulated voltage output (in this case, 5V 2A) that can be used to power something else (that’s the little plug in the photo.)  For fixed-wing aircraft this is normally a server to control the flaps or rudder, but on a quadcopter this isn’t that useful.  I’m not sure if I’ll use this feature or not.
Where: I ordered these from hobbyking.com but they had to come from China.  They were highly rated by the enthusiast community and also really cheap at $13 from hobbyking so I ordered 5 in order to have a spare.  Even when I factored in the shipping cost, these units were still about 3/4 what you could buy domestically for similar quality.

SlowFly PropsPropeller: Slow Fly 10×4.5 ABS propellers, $0.77 ea
Why: Supposedly these propellers are strong plastic designed for use on electric motors. Of all the things on my quadcopter design this is the one area where I can’t tell much about strength versus weight versus balance in terms of value.  I do know that I will be balancing them when they arrive but given how cheap they are I might also get some locally at a hobby shop rather than order them online in the future.  Obviously the quadcopter needs 4 and I ordered a set of black and a set of red (with extras) so that I can see the orientation of the quad by putting 2 red in front and 2 black in back.
Where: I ordered these with the other parts from hobbyking.com.

Battery: Turnigy nano-tech 2200mah 3S1P LiPo, 187g, $19
Why: I read good things about these batteries and  the run time some are getting from a single 3 cell battery.  I also learned to purchase the nano-tech variety due to the limited swelling during use.  According to one report, a traditional lithium ion batteries can increase in size by 15% due to heat during discharge.  I’m not sure if I will use one battery or two during flight so I ordered 3 while I figure that up.
Where: I ordered these from hobbyking.com because it was in the US warehouse.  If it had not been, I would have been looking for a local source.

My Quadcopter

AeroQuad Cyclone

AeroQuad CycloneI went to the Houston Mini-Maker Faire in January 2013 and for some reason seeing all the Star Wars droid replicas, electric cars, and 3D printers made me want to do something with the Arduino and/or Raspberry Pi I had sitting in my desk drawer.  I was charmed by the 3D printers but I honestly couldn’t figure out why I should build one.  But it was while looking at that hobby project that I found all the work being done on quadcopters and I found myself more interested in that than printing.  And then I happened to see a Nova special titled Rise of the Drones that captured my imagination in a big way.

I’ve always been a fan of RC planes having had them since I was a kid.  I’ve had several in my life including a gasoline powered control line model that was more scary than it was fun and a great park flyer that I still have.  And while I like them I’ve also had trouble with the speed and how fast it can get out of control.  RC helicopters on the other hand, were always more interesting to me but suffered from being more expensive and harder to fly.  At least that is how it used to be.  With modern micro-controllers, digital cameras, and cheap parts like accelerometers and gyros (thanks to the Wii, Sony Move, etc.) this has gotten a lot safer, easier, and opened up a whole new world of possibilities.

APM Planner

I have to admit, it got me dreaming of an autonomous copter flying around the area taking photos and providing a live video feed of its flight as it goes.  All that is possible, but I’m going to take a more measured approach and ease into it.  Sort of.

I know that I want an Arduino-based flight controller.  I like Arduino because it is a powerful modern micro-controller that is relatively easy to code to.  It is designed from the ground up as a real-time control system and that seems perfect for a helicopter.  After checking into it, there are several options that seem very viable.

One that holds great appeal is the MultiWiiCopter.  This project option combines a very inexpensive Arduino board with the insides of a Wii Motion Plus controller.  The Wii component is a very cheap way to get a set of gyros and acceleromters connected to your Arduino.  You can build one for about $50 which will act as the perfect platform for an RC-controlled quad as long as your comfortable soldering the parts (or you can order a board with all the pieces assembled for $93).  However, it isn’t really designed for autonomous flight.  You can add on a GPS/compass and other things but that isn’t what it was designed for.  I might get one of these at some point in order to learn how it works compared to others.

APM 2.5+ Module
APM 2.5+ Flight Controller

The project I ultimately decided to make is based on a project named ArduPilot.  Specifically designed for quadcopters now, ArduCopter is a robust solution with lots of enthusiast assistance in the form of blogs/forums/etc.  It also comes in a great physical package with all the components and easy-to use connectors.  With that in mind, I’ll create another post with all the details of what I have purchased so far, why (at least what my thinking was) and how it is going.