A while ago, I posted my first Instructable about how I built my first racing drone. It was a 250 size quadcopter, running 5 inch props. I still enjoy flying it, with a few upgrades, but with the rate this hobby has progressed, a lot of the information in that Instructable (and parts used for the drone) is very out of date. I also don't get to fly this quadcopter as regularly as I'd like as I don't have enough space nearby for something that big and powerful. I tried building my own micro brushed quadcopter to fly indoors, but it was a massive disappointment. The brushed motors it was using were fragile and lacked power so I pretty much gave up on it.

Recently, I came across micro brushless quadcopters, generally around the 130 size (130mm diagonally from motor to motor). They were small enough to fly in smaller parks, would not draw negative attention due to their small size, and could be built in order to be docile enough for indoor/ backyard flying as well as powerful enough to compete with bigger racing drones. I immediately knew that I had to build one myself!

Step 1: Parts Overview

These are the parts I chose to use:

Quattrovolante Q-Carbon 130 Frame: The main reason I chose this frame is its 3D printed canopy, which covers most of the electronics giving the finished quadcopter a very neat look. The variant of 3D printed skirt I chose supports the Piko BLX flight controller, adding to the convenience of this frame. The main plate is a sturdy 2.5mm carbon fibre and overall this is an excellent frame in my opinion.
Piko BLX FC+PDB: This is an extremely interesting piece of hardware. It runs a powerful STM32F3 processor and has the MPU6000 gyro connected via the SPI bus which allows it to run at very high refresh rates. It also has an integrated PDB (power distribution board) which supplies power to the four ESCs. It has a nice board layout, allowing convenient soldering of everything to it. It is also a good bit smaller than standard flight controllers.
RCX H1407 3200kv: 1407 is pretty much the largest size of motor that will fit on this frame. It offers a good bit more power than the 1104/1105/1306 size motors typically used on this size of quadcopter and weighs only a little more than 1306. 3200kv (3200 RPM per Volt) strikes a good balance between the torque needed for heavy propellers and top end speed. If you want to know more about brushless motor sizes/ kv ratings etc., do take a look at my blog post about this. I use both the RotorX 3040T (more efficient but less durable) and DAL T3045BN (less efficient and more durable) propellers depending on where I am flying.
FVT LB20A-S: These ESCs are rated for 20 Amps of continuous current draw, and are based on the BLHeli_S architecture that offers superior smoothness and throttle response. Despite being extremely tiny, they still take up most of the space on the arms. A 10-12A ESC may have sufficed for these motors but I wanted to be safe as I am running a 4 cell battery and some aggressive propellors and I didn't want to risk burning anything. I have also written a post on choosing the right ESC which may be helpful.
Aomway 200mW: This video transmitter works on the 5.8 GHz band, and transmits the image from the FPV camera to my goggles. I chose it because it is small, light and known to be reliable. I paired it with this cheap circular polarised antenna.
XAT520 camera: This is a really small camera with pretty good image quality. I chose it because I had heard it was quite good and it was on sale at the time I bough it.

Step 2: Putting It All Together: Hardware Setup

This was quite challenging due to the extremely small size of the frame. It also requires a high level of soldering skill and experience with building quadcopters. Definitely not recommended for beginners. Here are the steps I followed:

Mount the 3D printed skirt on the bottom plate. The screws for this are included with the frame are M2 size (you will need a 1.5mm head hex driver).
Mount the 3D printed motor guards and motors. The screws needed for this are not included. I used steel M2x6mm hex bolts. They are just long enough to grip the motors without touching the windings in the motors (which can burn them out).
Mount the video transmitter at the back of the frame using double sided tape. Mount the FPV camera at the front (there is another little 3D printed piece which goes right up in the front and supports the lens). I used hot glue to hold it in.
Solder the +5V and ground wires from the video transmitter to the Vin and ground (red and black) wires on the camera. Your VTx may not have a regulated output, or may output a different voltage which can fry your camera, so be sure to check the specifications.
Flash firmware to and set up the Micro MinimOSD (if you choose to use one). It will be very hard to access later so make sure to get it done now. An OSD basically overlays data such as battery voltage and RSSI (a measure of the signal strength your receiver is seeing) on your FPV feed. This tutorial explains the procedure needed to set up the OSD.
Solder the +5V, GND, Tx and Rx pads of the Micro MinimOSD to the Piko BLX using short lengths of wire. This allows the flight controller to send the battery voltage and RSSI data to the OSD. You can find the exact wiring diagram here.
Mount the Micro MinimOSD in the small space under the Piko BLX mounting area. Solder the video input wire from the camera and output wire to the VTx. I have attached the OSD pinout to this step.
Mount the Piko BLX to the skirt. Use nylon screws. I used M3x6mm screws that I cut down slightly as they were too long.
Solder the motor wires to the ESCs. Since the arms are so small, I would have to had cut the motors very short to solder to the ESCs. This could have caused trouble later, so I decided to go with the 'wraparound' method. I passed the motor wires under the ESC, back over it, soldered them on and put heat shrink tubing on the whole thing. My ESCs do not come with motor wires. If yours do, you will have to remove them.
Solder the battery lead and ESC power and signal leads to the Piko BLX. The black wire wrapped around the white signal wire can go to the same pad as the ESC ground. Also solder the VTx to the VTx power pads on the Piko (make sure your VTx can handle the full battery voltage). You should also solder on a buzzer, and the receiver (and telemetry wires if applicable). I used a FrSky X4R-SB with the pins removed but it was still a very tight fit. The canopy does not close completely. I would recommend a mini FrSky compatible receiver (if you're using a FrSky radio/ module) such as that sold by FuriousFPV or on Banggood. Again, you can find the complete connection diagram here.

That's it. I found this build video extremely helpful as well. Before you pop the canopy on, we need to go through the software setup.

Step 3: Putting It All Together: Software Setup.

I first flashed the Piko BLX with the latest version of Betaflight (3.0 RC12 at the time of writing). It is still in pre-release and may be buggy. If you want more stable firmware, you can find older releases of Betaflight and Cleanflight on the FuriousFPV website. I also flashed the ESCs to the latest version of BLHeli_S (16.3 at the time of writing) using the passthrough function on the flight controller and the BLHeliSuite software. This requires you to plug in the battery, so make sure the propellors are off and there are no shorts/ solder blobs (double check with a multimeter and use a SmokeStopper when you plug in the battery for the first time).

I then calibrated the ESCs from the Betaflight configurator software. I have attached pictures which show my current settings in both Betaflight and BLHeliSuite.

Once you have verified that your controls are responding correctly, it is time to put on the canopy and propellers and go fly. I found that loom bands are a good option to secure the canopy. There is a set of small hooks at the front and back of the canopy where you can wrap a loom band around the canopy.

Step 4: Let's Fly!

Flying this little quadcopter is great fun. It flies as well as I hoped it would and now I can practice FPV every day in the space I have near my house. If you have built any racing drones before, do consider a 130 size for your next build. If you are new to quadcopters, a 130 might be nice and small to start off with, but it takes a high level of skill and experience to build. If you are confident with your soldering skills, you may be able to do it but it is certainly challenging.

Enjoy!