How to Choose a Flight Controller for FPV Quadcopter
Picking the right flight controller that suits your needs is a daunting task. There are dozens of flight controllers out in the market to choose from, where each is better in their own way. With advancement in technology flight controllers have evolved greatly over the years with faster more powerful and better micro-controllers being used for better optimization of resources and features.
Technology has come a long way since the more popular and widely used KK2 boards. The early KK2 boards and their successors were bulky at 50x50mm as compared to the most modern F7 flight controller that are half the size and have more processing power.
Though there are a lot of parameters to consider before buying a flight controller, this guide tries to help you in selecting the best flight controller for your particular needs and simplify the buying process.
What is a Flight Controller?
Flight controllers (FC in short) are circuit boards that have particular sensors such as gyroscopes (helps to determine the angular orientation) and accelerometers (helps to measure the vibrations of motors) and several other insignificant but useful sensors such as barometer (altitude of the quad can be found), compass (provides orientation in relation to earth’s magnetic field) etc..,
But the functions of the flight controller’s do not end there. One of the major functions of a flight controller includes receiving and processing the input signals from the receiver and executing appropriate commands given by the users. Simply put, flight controllers might be compared to the human brain. The human brain tells us how to walk, in the same way flight controllers are the brains on a quad that tell the quads how to fly.
Flight Controller Processors
F1, F3, F4 and F7 are the most commonly used processors in mini quads. F3 was the successor of F1, F4 was the successor for F3 and F7 was the replacement for F4. All these 4 processors are based on STM32 architecture which uses 32 bit processing rather than the 8 bit on KK2.x boards.
As you can see with advancement in processors, the processing speed got higher. Higher the processing speed faster can it execute the commands. The fastest F7 processor can execute 216 million cycles per second (A cycle is the basic operation such as fetching or accessing memory or writing data).
F1 processor is the oldest processor and has the lowest processing capability of all the above processors. It is actually an outdated processor with Betaflight ending support to F1 FC’s in 2017.
F3 was essentially a F1 FC with increased number of UART’s (It is discussed in detail below) and increased flash memory (memory used to store the FC’s firmware codes). Some smaller FC’s use this processor even now because of their compact size and exceptional processing power.
With developments in Betaflight optimizations taking place constantly, F3 processors are having a hard time keeping up.
F4 was a giant leap in mini quad processors with more than double the processing power that of an F3. But there are limitations with F4 processors with no support for smartaudio natively which is not a big deal for most people. Still F4 FC’s are the most popular choice for their functionality and affordability.
F7 processor is the big daddy of mini quad FC’s. F7 FC’s became available mid of 2018 and these are the most recent processors. F7 FC’s are packed with upto 8 UART’s which can be used for telemetry, GPS, camera control etc.., F7 FC’s come with dual Gyros (MPU6000 which is noise resistant and ICM20602 which can run 32K gyro sampling).
Obviously F7 is more future proof and more and more Betalight developments are going to be geared towards optimizing the processing power on an F7 processor.
Betaflight, Cleanflight, Raceflight, KISS are some of the major flight control firmware’s widely used in flying a mini quad. Each firmware is optimized for a particular function.
Betaflight is the most popular option with its easy GUI (graphical user interface) and under constant development by its developers. Betaflight is flexible and a powerful flight controller firmware perfect for a beginner which requires little to no coding experience. Another major advantage that Betaflight has is that it supports a large number of flight controllers.
Another flight control firware is Raceflight, focused entirely for acro and racing drones. Raceflight stands out by deleting non essential codes (like GPS). By deleting these codes Raceflight freed up processing power which can be used to do other useful functions like running faster looptimes for example.
If you’re only into racing, Raceflight is the firmware to choose. But beware when selecting, flight controllers such as the Revolt F4 are capable of running Raceflight.
KISS (keep it simple stupid) is a closed source firmware developed by FlyDuino. KISS products are powerful and up to date with the current trends on the market. Similar to Raceflight, KISS is also closed source and runs on proprietary boards from KISS. If you like Apple products despite its higher price point then KISS is the Apple of the mini quad world.
Hardware is probably one of the most important aspects to consider when selecting an FC. Hardware of a flight controller decides how well a quad performs because quality components assure accuracy, efficiency and performance.
IMU- Gyroscope & Accelerometer
IMU stands for inertial measurement unit. IMU consists of Gyroscopes (gyro in short) and accelerometers. A single IMU chip contains Gyro’s and Accelerometers. Since most pilots fly acro mode, accelerometers are turned off.
Gyroscope is a sensor placed in FC’s which helps to determine the angular orientation or tilt of the quad.
There are 2 major Gyros used in the world of quadcopters. They are the MPU6000 and ICM20602. F4 FC’s use MPU6000 gyros, while F7 FC’s use ICM20602 and some FC’s have dual gyro setups featuring both the ICM20602 and MPU6000 which can be switched according to the user preferences.
The MPU6000 gyro was launched in 2010 by InvenSense. This is an older gyro which is reliable and more noise resistant than ICM20602 with gyro sampling capability at 8KHz. ICM20602 is a much latest gyro by InvenSense which is much more sensitive and has the capability to sample gyro at 32KHz.
Further reading: Gyroscopes and Accelerometers
The sensitivity of the ICM20602 might be a good thing and an equally bad thing. Technically the ICM series gyro must perform better because of their sensitivity but not necessarily. The mechanical vibrations from the motors require the FC to soft mount the gyro and the electrical noise from motors and ESC’s require the addition of capacitors to counter electrical noise. But when properly setup the ICM20602 can do better than the ICM6000 in every way.
UART stands for Universal Asynchronous Receiver/Transmitter. UART is the hardware interface that allows the users to connect multiple devices such as camera OSD control, VTX channel control, serial radio receiver etc.
UART has 2 ports to transmit and receive data. A FC may have TX4 and RX4, where TX4 stands for UART 4 transmitter and RX4 stands for UART 4 receiver. The image depicts the TX3 (UART 3 transmitter port) and RX3 (UART 3 receiver port).
Prior to 2014 FC’s used to have up to 20 UARTs on a FC where people need not worry about running out of UART ports. As manufacturers wanted to miniaturize FC’s which they did was at the expense of lesser number of UART’s with 8 being the most number of UART’s found on a modern day F7 FC.
If you plan to run telemetry or smart-port or even GPS for a long range rig and a whole lot of other peripherals that may require UART’s, you are going to have a hard time finding UART ports. You have to prioritize your peripherals and choose accordingly.
As a beginner you probably won’t be running GPS or any other advanced features like telemetry on your first quad. You are just beginning your FPV journey UART must not be that much of a concern.
PID, PID Tuning and PID Analyzers
PID stands for Proportional, Integral and Derivative. PID is a means of correcting an error from the various sensors placed on a FC such as gyroscopes. PID tuning is a very difficult process and is a whole another subject that requires separate guide.
Simply put the input from the users must be interpreted by the FC and executed appropriately. Since we are not on the quad flying it we need assistance from the FC to get the quad to orient as required. The process of orientation is executed by 3 parameters know as PID. These 3 factors govern the handling and the behavior of a quad.
For further reading and in depth knowledge about PID
The “P” parameter governs the orientation. A quad moves by changing its orientation in the air which is done by adjusting the power of the motors. Increasing the “P” value also increases the responsiveness of your quad.
“I” parameter governs for any possible errors caused by external factors on the quad such as sudden gust of winds. Increasing “I” determines how fast a quad is going to respond to your inputs.
“D” parameter dampens the effects of “P” parameter in case of errors or overshooting of inputs. “D” can also eliminate oscillations and amplify it.
Further reading: In depth knowledge about PID
One of the latest news buzzing around the world of quadcopters is PID analyzers. Most beginners cannot successfully tune a drone such that there is no vibration and most beginners can be seen on the internet asking the pros for help regarding the problems and a suitable solution. This is where PID analyzers come into picture.
If you have black box feature enabled you just feed this data into the PID analyzer which will give users the required settings or the recommended settings for smooth flying. If the FC is capable of black box data logging, PID analyzers are worth a try.
Further reading: PlasmaTree PID analyzers
GPS stands for global positioning systems. GPS is a satellite based navigation system that provides geolocation for a GPS receiver anywhere in the world. Why use GPS in quads?
Smaller quads are relatively cheap to build and losing them won’t hurt your pocket that much. But as you move bigger in size like 650mm or even a 1000mm cinematography quad frame, the parts alone for the build will cost a couple thousand dollars. Hence GPS are added to avoid mishaps and GPS can be referred to as insurance.
Not only is it useful to identify lost quads, some quads with autonomous features such as Aerial mapping requires GPS. GPS is mostly used for quads that fly beyond VLOS (visual line of sight) and totally unnecessary for close proximity flying as you can just walk over the area you flew and normally find the quad hiding in a bush.
As the name suggests, a current sensor is used to measure the amount of current your quad draws at various throttle ranges.
Why is it necessary? Because you can monitor your current and be sure that you are not damaging your battery by drawing large amounts of current. Not only measure and monitor current, a current sensor can also give the battery consumption (mAh) used from the battery.
Normally current sensors are placed on PDB’s or on the ESC’s, if not they can be mounted separately or even buy current sensor integrated FC’s.
Barometer is a type of sensor that measures the altitude by sensing the atmospheric pressure. As we all know atmospheric pressure decreases as we go up higher in altitude, if you didn’t know prior to this you know it now.
Barometers are used for autonomous navigation where the quad is required to hold a certain altitude throughout its flight path. The F7 flight controllers are so powerful that manufacturers decided to add sensors to utilize the extra processing power.
We normally don’t need Barometer sensor on our quads as we don’t do autonomous flying, but if you do long range quads the Barometer sensor might be helpful.
On Screen Display (OSD)
OSD stands for on screen display. The function of an OSD chip is to overlay information from the various sensors and display parameters such as battery voltage, current consumption, GPS location, altitude etc. These information gets transmitted with the video feed from your FPV camera.
Betaflight OSD has features that a FC can be programmed to display, like an artificial horizon (the straight line in the middle), display airspeed (if an airspeed sensor is present), GPS coordinates (if GPS sensor is present), current consumption and mAh consumed (if a current sensor is present) and so on. Below is a list of OSD elements that you want to be displayed on your goggles.
Power Distribution Board
FC manufacturers wanted something unique to sell more of their products and PDB integrated FC’s are the result of this venture. Though integrated PDB’s on FC’s eliminate the need for an external PDB, it also reduces the height of the stack by up to 15mm. FC integrated PDB’s are ideal for frames with tight spaces but they come with their own set of challenges and disadvantages.
Even though these types of FC’s reduce the height of the stack, they are prone to electrical noise interfering with the gyro. As the current flow is very close to the flight control processors and gyros, voltage spikes and electrical and magnetic interference may cause some issues. That being said manufacturers claim that they are well isolated from electrical noise.
Battery Elimination Circuit (BEC)
Apart from supplying power to the motors there are loads of other components on a quad that require power such as camera, vTx, receivers etc… A good flight controller will have a good amount of BEC’s from 3.3V from SBUS receivers, 5V BEC’s for PPM receivers and 12V BEC’s for camera, vTx and LED’s.
If you are going to use individual ESC’s and PDB for powering your motors then the PDB will have BEC’s for every component that requires power. But If you plan to go the 4in1 ESC route, then pay attention to the BEC’s present on the FC’s.
Black Box is something similar to that found on airplanes where all the data from the quad is stored. This Black box data is stored in the SD card which we plug in the slot.
Black Box is something similar to that found on airplanes where all the data from the quad is stored. This Black box data is stored in the SD card which we plug in the slot.
Black box helps us to analyze data of every parameter such as voltage draw, current consumption and such so that they can be analyzed later on the ground. If any oscillation or vibrations are noticeable then the black box data can be fed to PID analyzers to identify the necessary corrections and tune your quad.
For getting started with Black box logging
Manufacturers took a step even further into integrating things by integrating FC and ESC on a single motherboard. The Asgard FC’s were the first FC’s to integrate ESC’s into the FC’s for ease of use and simplicity. These type of FC’s require not much of soldering as the ESC and FC are internally connected saving the hassles of wiring for a beginner. The Asgard board weighs a total of 14g which is a good amount of weight reduction plus the weight gained by not using wires.
But all these features come with a penalty. There is only so much you can cram into a 36x36mm board, ESC integrated type of FC’s usually tend to have smaller MOSFETs (MOSFETs are responsible for the current carrying capacity of an ESC, larger the FETs larger the current carrying capacity). They will be fine for micro builds of 3” and under but can’t handle the current draws of larger 2207 or 2306 motors without damaging the FC.
If you already own a transmitter, then receiver compatibility is one feature that you should definitely check before buying. RC transmitters use different protocols to communicate with the air borne receiver where different radio manufacturers use different protocols. Some of the major RC protocols are PWM, PPM, IBUS, SBUS, DSMX, DSM2, XBUS, CRSF (Crossfire) to name a few.
Although most modern FC’s have all the above mentioned receiver compatibility there are some FC’s that do not support a few protocols (it is probably how they are built). So it is worth taking a look into the FC receiver support list and make sure it supports the protocol used by your particular radio.
Further reading: RC radio protocols
Soft mounting FC’s and Gyro’s
As the motors come to life when flying, they tend to produce vibrations which travel through the frame and affect the accuracy of the gyro placed on the FC. No matter what the motor quality is and how precisely the motors are manufactured, they produce vibrations. Hence to counter act this tendency, the gyro has to be isolated and the 2 methods to isolate the gyro is by either soft mounting the FC or soft mounting the gyro present on the FC itself.
Soft mounting is a must for FC boards that use ICM20602 gyro or they just become unflyable due the sensitiveness of the ICM20602 gyro. Soft mounting definitely help to soften the mechanical noise generated by the motors and wouldn’t hurt to use some sort of soft mounting.
The most common mounting pattern used in a quadcopter is 16×16 (for 2” and under quads), 20×20 (for 2” to 4” quads) and 30.5×30.5 (for 4” and larger quads). This is the distance between each hole in a FC. Each and every frame has a mounting pattern mentioned for buying suitable FC boards.
Some frames have support for 20×20 and 30.5×30.5 holes. Hence pick a suitable sized FC board that fits your frame.
Of course there are a lot of things to consider when buying a suitable FC and you may as a beginner feel overwhelmed at first. Even I was a beginner a few years back and once I spent a few weekends trying to learn the basics of quadcopters, I haven’t had the need to look back.
We suggest you to read this article thoroughly if you skipped somewhere when bored and when you have a good knowledge of things you will not feel the need to search the web for articles to learn the part you skipped.
If you are still skeptical and not confident enough in yourself we have a few recommended FC’s below.