I have built & modified a few quadcopters of various (small) sizes, from the tiny brushed-motor nano-quads like the HobbyKing Pocketquad & Syma X1 to a larger, more traditional brushless motor mini quad based on the Turnigy 345mm frame. (More on that in a subsequent post.)
Throughout this endeavor I've been using (and customizing) the MultiWii flight control software, with various Arduino / Atmel-based flight control boards. It's becoming a FAQ what hardware and systems I'm using, so in this post I'll detail my current setup. Future posts will cover updates, new hardware, and a couple of crazy projects I'm working on. ;)
Note: I buy a lot of parts made and sold by HobbyKing.com in China. Their website is a bit... odd.. so I'll include the full name of each product in case the link to the product stops working as HK links tend to do. Just search for the title of the item to find it if the links don't work.
Control Transmitter:HobbyKing OrangeRX T-Six DSM2 Six Channel Transmitter (Mode 2)
Notes: I bought this transmitter because I wanted a DSM2 2.4GHz system, and it was cheap. It's perfectly adequate, but I would eventually like 8 channels and the ability for the aux channels to have more than just "on-off" capability, so I might consider a Turnigy 9XR with custom firmware and the DSM2 TX module in the near future.
First nano quad: The HobbyKing Pocket Quad v1.1
HobbyKing Pocket Quad
Notes: This is a pretty cool nano quad, but a note for the uninitiated: It is not ready-to-fly. It requires working knowledge of Arduino to get it set up, and some experience with Multiwii is helpful too. It was a steep learning curve to get everything working on it. For the firmware, I used rcgroups.com member Cesco's PQ customization of Multiwii which includes required changes for driving the mosfet / brushed-motor combination.
Once you get it working, though, it's a blast to fly, especially indoors. It's agile enough to fly outdoors, but it's small enough that it's easy to lose your orientation and lose control of outside. So be careful if you fly it outdoors. I've now actually lost two of these things outside and not been able to find where they came down. :-P
There's a long thread about the Pocket Quad (and its variants) at rcgroups.
Second nano quad: The Syma X1 MultiWii Conversion
My current brushed-motor quad of choice is a modified Ready-To-Fly Syma X1 from Amazon. Note, this thing comes ready to fly with an AWFUL cheap transmitter, and a flight controller that basically flies like a school bus drives. It works, but it's not terribly exciting.
What I like about it, though, is the tiny carbon-fiber arms and the motor / gear / propeller combinations. So, I bought it, gutted it, and replaced the flight control board with this really nifty Micro MWC flight control board from HobbyKing. This FC is based on the Atmega328p, which I'm not a huge fan of, but it's plenty capable in this form factor as its worthwhile to sacrifice secondary UARTs and other such capabilities to get such a tiny and light package. Seriously, the thing is the size of a postage stamp, includes the mosfets for the brushed motors, an integrated DSM2 receiver, and weighs < 2g.
The X1 is hilariously fun to fly with a MultiWii flight controller. I can set the PID settings how I like, jack the rate up through the roof, and make the thing do crazy flips. It becomes agile enough to fly outdoors on a windy day despite it's ridiculously light weight, and it's resilient enough to fly it into the ground without damage.
Note: Another similar option for this conversion is the WLToys V929
Important info about that HobbyKing Micro MWC flight controller, including instructions and custom firmware (again from Cesco, the king of "brushed motor" MultiWii modification) is in this long thread from rcgroups: http://www.rcgroups.com/forums/showthread.php?t=1993117
More to come about my larger flying toys...