Autonomous FPV Drone Build Log

Fun Classwork: Combining an Autonomous Flight Controller with an FPV Style Drone 

Fall 2020 has been off to a rough start with covid-19 restrictions and unrelated personal medical emergencies that caused a late start to my semester. Fortunately the university was prepared for virtual courses because of covid, so I got lucky between accommodating professors and a situation that was already setup for my situation. 

Anyway, this drone sensors course has been a fun break from some intense classes. The goal here is to build an autonomous drone using the Ardupilot software. Students can choose to use S500 style drone parts from the university or buy their own drone to build. I chose an FPV style drone, the Xilo Phreakstyle Bardwell edition. This kit was chosen because it would be my first FPV build and it allowed me to be lazy. Or so I thought... As it turned out, replacing the Xilo F4  FC with the Pixhawk mini 3DR added a lot of problem solving to this build. Lets get into it...

What I plan on doing, more or less. Made with Fritzing
(which doesn't have all the parts so I made due with protoboards)

Parts in this build:

• Xilo Phreakstyle frame
• Xilo Stax 4in1 ESC
• Xilo Micro Mutant FPV camera
• Xilo Stax VTX
• Xilo 2206 2600KV Stealth brushless motors
• Xilo AXII antenna
• PIXHAWK Mini 3DR Autopilot System
• Generic Mini OSD
• FrSkyXM+ Mini receiver
• 3S/4S LiPo battery

Equipment used:

• Flush cutters
• Various micro screw drivers
• Various hex keys
• BetaFPV Radio Lite 2 controller*
• DJI FPV goggles*
• Eachine Pro 58 analog diversity receiver*
• Analog adapter from Fatshark receiver module to DJI FPV**
• LiPo charger

* Equipment is just what I have, any analog goggles or controller will work as long as it matches the frequency of the VTA/receiver in the drone

** Only needed for convenience with the DJI FPV digital goggles

So, let's walk through what all those parts are and what they do.

This is an autopilot system. This one is specifically a PIXHAWK Mini 3DR, which requires 5V of power input to operate. Course requirements necessitated an Ardupilot compatible autopilot system (where Ardupilot is the software the autopilot runs), however there are other autopilot systems. This is the brains of the drone, it tells everything on the drone what to do based on either programmed flight routes from software or the operator with a controller.

This is the power system, the drone's digestive system (to continue the analogy from above). The battery provides electricity for the drone to run. LiPo batteries are classified by the cell count and voltage, where a 3S battery contains 3 cells of 3.7V each for a total of 11.1V when stable. Wait a minute, stable? Well yes, LiPo batteries are not the most stable battery, this is not a better AA battery. LiPo batteries have a fast discharge rate and great weight to power ratio. This means the drone call pull large amount of Amps (power) from the battery to accelerate hard without weighing the drone down. You may also notice the battery has two plugs; one plug is for ensuring that each cell charges evenly and the other is the main power in/out. In this drone, the battery plugs into the ESC and is also connected to a capacitor. A capacitor hold a small amount of power when connected and can discharge instantaneously when power drops, this evens out the power draw for a more stable power supply. It's not really necessary to know the details, just make sure the cap is oriented correctly (big white stripe with - to the negative side). Once power reaches the ESC, it can be distributed to the rest of the build. This 4in1 ESC is actually a power module, 4 ESC's, and a power distribution board all in one piece. This simplifies the build, but trades off the ability to replace one component if it fails (aka if one ESC burns out, then the whole board is dead). It is common to use an all in one power board such as this. The power module and distributor take the power from the battery and make it available to the rest of the drone. Power is passed through a port to the fc/autopilot at 12V in this drone and to the ESC's. ESC stands for Electronic Speed Controller, which controls and provides the correct power to the brushless motors. The fun part of ESC's is that the motor wires can be attached anyway you want as the ESC is the part which defines what wire does what.

Brushless motors use the magic (read: physics) of magnets and electromagnetic inductance to create motion. What does that mean for you? Just that there are no mechanical connections (like in brushed motors) to wear out. Unless you physically deform the motor, it can run like brand new over its whole life. This part of the build is fairly straightforward; the motors hold your propellors and spin fast enough to create lift.

The FPV camera is what makes this an FPV (First Person View) drone. It is just a little camera on the front of the drone that provides a live video as if you are in the drone flying it.

The VTX, or video transmitter, is how the video from the FPV cam gets to the operator's goggles on the ground. The VTV is connected to the power board for 12V power and the camera for the video feed. This one sends an analog signal at 5.8GHz. Optionally, I have put an OSD (On Screen Display board) between the camera and VTX. This connects to the FC/Autopilot system to provide information on top of the video feed. This is useful as I can see the actual charge of the battery, stopping battery over-discharge and the drone falling from the sky if I don't land before it cuts off. It can also tell me how good of a signal (RSSI) the receiver is getting. 

The receiver receives commands from the controller and relays them the fc/autopilot system to control the drone. This one uses a communication protocol called SBUS which the autopilot can understand. It is important your receiver com protocol can be understood by the fc/autopilot. The receiver must also be connected to the controller via a protocol it can understand as well. Mine uses the FrSky D16 FCC protocol (FCC as I am in the USA, where the EU has another D16 protocol, they can usually be flashed/programmed between the two in firmware/software). Some controllers use other protocols though, so it's worth double checking or getting a multi-protocol controller. My BetaFPV Radio Lite 2 can do FrSky D8, D16 FCC, and D16 EU out of the box; some have even more options. Once you have a receiver that can communicate to both FC and controller, you need to bind it to the controller so it will only take your commands. Hold the only button on the receiver and then power it on. This puts it in bind mode, allowing your controller to connect when it's in bind mode. Controllers vary in how to bind so consult  your owners manual. 

Frame

The frame is simply what everything is sitting on. There are various shapes and sizes, all with pros and cons. But, it mostly just depends on what you like. You do you.