FPV Drone Project: Part 1
I’ve been wanting to build an FPV quadcopter for a number of years. This summer, with my Unmanned Systems master's program in the rearview mirror, I decided to embark on the journey of purchasing, assembling, and flying an FPV drone.
I chose the HolyBro QAV250 system for two main reasons. First, this drone was available as a kit, which included all parts except for a receiver (Rx), transmitter (Tx), batteries, battery charger, and FPV goggles. Later I would find out that selecting high-quality and compatible parts was not a quick and easy task. Second, this system utilized a stack that I wanted to gain familiarity with: Pixhawk 4 Mini autopilot, PX4 flight control software, QGroundControl GCS, and the Micro Air Vehicle Link (MAVLink) communication protocol. Having these elements was key since this stack is commonly used in larger VTOL and fixed-wing systems.
QAV250 Complete Kit
After graduating, I finally pulled the trigger and purchased the Holybro Pixhawk 4 Mini QAV250 Complete Kit from Banggood. The 915Mhz telemetry radio was chosen over the 433Mhz system because the drone will be used solely in the United States. The FCC has set aside 900Mhz (alongside 2400Mhz and 5000Mhz) for unlicensed Industrial, Scientific, and Medical (ISM) applications. The 433Mhz band is meant specifically for Europe.
The contents/specs of the complete kit:
- Pixhawk 4 Mini autopilot
- Carbon fiber 250 airframe with hardware
- Motors - 2206 KV2300
- 5” Plastic Props
- Pixhawk4 GPS
- Fully assembled Power Management Board with ESCs(BLHeli S ESC 20A)
- 915MHz Telemetry Radio
- Power and Radio Cables
- Battery Straps
- Dimensions: 198*235*85mm
- Wheelbase: 250mm
- Weight: 440g
Receiver (Rx) and Transmitter (Tx)
To ensure compatibility, the search was on for a receiver and transmitter from the same manufacturer. Several manufacturers came up when searching for applicable units: RadioMaster, Spectrum, Futaba, FlySky, FrSky, and many more. FrSky came recommended from a co-worker who built FPV systems in the past. FrSky was also referenced in past QAV250 kits I decided on a $200 mid-grade transmitter, the FrSky Q X7S. Purchasing this controller ensured that there were adequate switches and channels for a future VTOL UAS build. Another benefit of this controller was that there were no additional batteries and chargers to purchase. The controller came equipped with two 18650 Li-Ion batteries and the ability to charge using an (antiquated) Mini-USB cable. The Q X7X also used FrSky’s latest ACCESS protocol. The faux carbon fiber version was selected to match the carbon fiber frame of the QAV250.
FrSky Taranis Q X7S ACCESS Transmitter
FrSky R-XSR Receiver
Selecting a compatible battery and charger was also a rabbit hole to ensure performance and compatibility with the rest of the system. After flying drones for five years, I was familiar with how voltage and mAh values related to drones. But what was a C rating? How many S did I need? The C rating relates to how quickly a battery can discharge. A high-performance FPV drone discharges at a higher rate than your typical consumer camera drone. Therefore, an FPV drone needs a battery with a high C rating. The S value describes how many cells are contained within the battery. A 1S battery has one cell while a 4S battery has four cells. As an extreme example, the DJI M300 utilizes 12S TB60 batteries. These relatively enormous batteries are 12 cell LiPos with a voltage of 52.8V. For my modest quadcopter build, I chose 14.8V, 100C, 1500mAh batteries as shown below.
GOLDBAT 4S 1500mAh 100C 14.8V LiPo Battery
Tenergy TB6-B Balance Charger
This blog post was a quick overview of the process I used to purchase parts for my FPV drone project. There are a number of great resources and videos that go much further in-depth into each of these components. Follow me in Part 2 as I begin to assemble and troubleshoot the QAV250.
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