Flight Controller (FC)
The Flight Controller (FC) is the Heart and Soal of your multi-rotor. In many ways, it's just a computer. In that, it's a motherboard that has a MicroController Unit (MCU), which is equal to a PC's CPU, RAM, & Hard Drive all in one. These MCU's also have ports just like PC's having USB/Display ports, FC's have Serial Ports referred to as UARTs. Although all FC's do have a USB port, it's not for connecting devices, it's the Management Interface of the FC. UARTs are used to connect to all other components of the multi-rotor. FC is one part hardware and one part firmware (software).
Flight Controller (FC)
The main job of your FC is to translate user input from the RX, compare that to the gyro (movement) data coming from the IMU, and then send commands to the ESCs to make the drone do what you want. We will list out the components that make that happen. As our hobby has grown over the past few years, we are asking more and more from our FCs themselves. Which has given birth to All-in-One (AIO) FCs. The question of "what is ALL", is a hard question to answer these days. We will also list out other common components FC could have as well. Finally, we will list out typical Solder pads FCs are expected to have.
FC PCB Anatomy
List of Main components on all FC
|MCU||The processor of the FC. Today almost all FC's use MCUs manufactured by STMicroelectronics. Specifically using their STM32 family of 32-bit Arm Cortex microcontrollers. Like most processors, there are different performance levels you can purchase. For our typical multi-rotor FCs, we use STM32 F1, F3, F4, and F7 controllers. Of course, F1 being the slowest, and F7 being the fastest. As of today, F1 FC's are completely deprecated, and F3 FC is very close to becoming deprecated in the hobby. MPU also is where firmware (like BetaFlight) and settings are stored.|
|IMU (Commonly referred to as Gyro)||Inertial Measurement Unit, is an electric device (MPU) that has both 3-axis gyroscope and 3-axis accelerometer sensors at a minimum. IMU's measures and reports a body's specific force, and angular rate. The main job of that IMU is to detect multi-rotors movement on all axes. There are other IMU's in the industry that have magnetometers (compass sensor) to detect North. Mini-quad FCs commonly use IMUs from InvenSense. The MPU-6000, MPU-6050, MPU-6500, and ICM-20602 are some of the most popular. Here is a link talking about them.|
|UARTs||Universal Asynchronous Receiver/Transmitter, are just serial ports used to connect to all components of the multi-rotor. Each FC has a predetermined amount of UARTs, typically ranging from 2 to 5. The determination of how many UARTs are available comes from both which MCU used on the FC and FC Manufacture in the way of Solder pads (Also the Firmware Target). Typical components the use UARTs are Receivers (RX), Telemetry (SmartPort), vTX Control (SmartAudio), OSD, Blackbox flash memory, etc.|
|Voltage Regulator (aka BEC)||All FC's have two regulators for 5-volts and 3.3-Volts. Some FC's can have other regulators for other voltage levels between 9-12 volts for running components like FPV camera or vTX. Each regulator supports between .5 to 3 Ah. Which can be important to know since powering devices like RX, LEDs, FPV Camera, vTX, etc. off the FC is becoming more and more commonplace.|
Other FC components
|OSD||OnScreen Display should be in the list above, as more often then not your FC will come with OSD chip that supports your variant of BetaFlight OSD software. Before the OSD was a separate component (could be aka MinimOSD) in the multi-rotor that ran between your FPV camera and vTX. That OSD would get data from the FC over a UART. It would run a variant of OSD software like MWOSD. Today, most FCs have the MAX7456 (or AB7456) chip built-in to the FC and uses FC's Firmware (e.g. BetaFlight) to run OSD. This way the Video Out from your FPV camera and Video In from the vTX would run to your FC and doesn't consume an available UART.|
|SD Card/Onboard Flash||Another very common component to have on your FC is a storage area for your BlackBox Logs. One of two options could be built-in to the FC. The First is to have OnBoard flash memory chip. Typically giving about 16 MB of storage. Secondly, an SD Card slot allowing us to use a wide range of SD cards that would support >2 GB of storage.|
|PDB||Power Distribution Board. Not too long ago, a very typical quad build would include a separate PDB that would supply power to everything in the quad. The downside to this design is stack height. With the latest quad frame designs being much more compact than ever before. Therefore combining both the PDB and FC made sense, since many FC's already had onboard BECs. No need to have another component supplying voltage to your quad. Another benefit of FC's with PDB can speed up the build and repair processes for those of us using or preferring single ESCs.|
|RX||Many TinyWhoop FC's and a hand full of 5" FC have the RX built-in. No need to solder cables between your FC and RX anymore. The Bind button will be somewhere of the FC layout.|
|vTX||Not too well-known, but there are FCs with built-in vTX. Much more common in the Mirco size quads then Mini's.|
FC Solder pad & Labels
List of FC Solder Pads (Pins)
|Pad Type||Description||Common FC Label|
|ESC signal||Next to the RX and Gyro (IMU) connection, the most important connections to any FC is the ESC Signal pads. All FCs will label these pads with M# represent the motor number of the quad. The number of pads can vary between 4 to 8. But 4 is much more common these days.||M1, M2, M3, M4|
|UART||All FC will have pads for the available UARTs of the FC. They will be a label with both a number and a TX (Transmit/Send) or RX (Receive). E.g. TX3 = UART 3 Transmit and could be used with SmartAudio. RX2 - UART 2 Receive and can be used with your RX SBUS. *||TX# or RX#|
|Power||All FC's will have pads for 5v, 3.3v or other voltage rails. This will come in two forms. Small pads throughout the FC's PCB layout, strategically placed where power is needed for a given component. Or larger bus bar where all your 5v connections will go. Sometimes there are even voltage selection pads where bridging two pads will supply either/Or. Typically 5v or VCC (Battery voltage). The pads will be labeled like 5v, 3.3v, VCC, or GND for ground. Of course, if the FC has other voltage regulators you will see a pad labeled for the voltage.||5v, 3.3v, VCC, GND|
|Video In/Out||If the FC has a built-in OSD (in most cases it will) you will have a pad for both Video in and Video Out. Typically labeled VIN (or VI) or VOUT (VO). The placement of these pads very between FCs. Sometimes the pads are next to each other, and other times they VI is at the front of the FC where the FPV Camera is, and the VO is on the back of the board where it is common to have the vTX.||VIN(or VI) VOUT(VO)|
|Voltage/Current ADC||If the FC gets power from the external component like a PDB or 4in1 ESC. Then there will be pads for getting both battery Voltage and Current reading from a current sensor. Commonly labeled as VCC (or vbat), and Curr. These pads tell the FC what the battery voltage is and how much power is being consumed and how much has been consumed. This data is feed into both OSD and telemetry to your radios.||VCC(vbat), Curr|
|Buzzer||For an external buzzer. There will be a + and -.||Buzz + / -|
|RSSI||RSSI analog input from RX||RSSI|
|Camera Control||OSD of the FPV camera can now be controlled via FC. The Cam Control is done the same way OSD CMS is controlled||CAM_C|
|I2C/SPI/SWD||Not typically used by most hobbyists. I2C and SPI are other types of connection protocols to the MCU. Commonly used with GPS sensors are SPI or I2C. SWD is used by designer/developers for Debugging what the MCU is doing.||SDA, SCL|
- Note: Some UART pads are dedicated to exact uses (like SBUS) because the UART has external inverters. Very common on F4 FCs as F4 MCU doesn't have hardware-based inverters. We F3 and F7 MCUs don't have this problem.
Not all FCs are manufactured the same way nor are they the same size. What is standardized is the mounting holes. FC sizes:
- 30.5mm x 30.5mm (4" and greater)
- 20mm x 20mm (2" to 4" although some 5" frames can have both mounting holes)
- 16mm x 16mm (2")
- TinyWhoop size
All FCs will have an arrow indicating where "Front" is. This is in relation to the ICM placement and position on the FC itself. Another more important factor in orientation is the Motor layout. Some FC believes Motor 4 is Top Left, where other FC's believe that Motor 1 is Top Left.
New FC Advancements
The hobby and FC technology are still rapidly growing. We are now seeing FC coming with Dual Gyros (IMUs), Multiple MCUs, supporting 2 FPV cameras, and more to come.
FC Manufactures Page
Here is a list of Manufactures