The FPV Drone Electronic Speed Controller (ESC) on a drone is a hard-working, powerful component. The ESC connects the flight controller and the motor. Given that each brushless motor requires an ESC, a quadcopter will require 4 ESCs. The ESC takes the signal from the flight controller and power from the battery and makes the brushless motor spin. Although it sounds simple, it is anything but! Although some micro drones use brushed motors, the mini quads used in racing and freestyle rely on brushless motors. Like the name implies, a brushless motor lacks contacts, or “brushes” inside the motor. The brush acts as what is called a commutator, which uses physical contact of the motor’s windings to spin the motor. Because they lack the brush, brushless motors use a different way to turn direct current (DC), the one-way flow of electrons, into a type of alternating current (AC). This is performed externally, through the use of an ESC.
Different Types of FPV Drone Electronic Speed Controller
Like everything else in drones, the ESCs continue to evolve and adapt to the demands of the pilots. ESCs play a crucial role in the performance of the drone, therefore the ESCs hardware continues to improve. There are a few basic types of ESCs available. Most ESCs on the market are controlled by onboard 32-bit processors, running firmware called BLHeli_32 (pronounced B L Heli 32) or KISS. As recently as last year, most ESCs were only using 8-bit processors, with only a few top-end ESCs like KISS being 32-bit. 32-bit ESCs can communicate with faster digital protocols, such as D-SHOT 1200 (compared to D-SHOT 600). 32-bit ESCs are also capable of other features such as controlling light-emitting diodes (LED’s), changing direction of motor rotation for features like turtle mode (automatically righting a flipped drone with the motors). These ESCs are also capable of telemetry, whereby information from the ESC such as RPM, amp draw, and temperature are sent from the ESC to the flight controller. Although the features of the 32-bit ESC are nice additions, many current 8-bit ESCs continue to perform incredibly well running the widespread ESC firmware called BLHeli_S.
Another consideration for ESC hardware is whether the ESC is an individual unit, attached on the arm of the drone between the flight controller and the motor, or a 4-in-1 ESC in which all 4 ESCs are combined into one circuit board and mounted in the main stack under the flight controller. For lighter builds, or for a cleaner look, many pilots choose to purchase the 4-in-1 ESCs. Often they come with built-in voltage regulators and can act as a power distribution board (PDB) as well.
FPV Drone Electronic Speed Controller Ratings
ESCs are rated based on how much current they can pass to the motors. The job of the ESC is to switch on power to the motor coils at incredibly fast rates. This switching is controlled by a microprocessor and carried out by transistors called MOSFETs, commonly referred to as FETs.
The size and quality of these FETs determines how much current (amperage) can pass through the ESC. Most ESCs will have ratings such as ’30 amps’ or ’25 amps’. These numbers generally represent the sustained current the ESC can handle. For short periods of time, generally less than 10 seconds, ESCs can handle slightly more current. It is common to see an ESC labeled a ’30 amps’ ESC that is capable of a 40 amp ‘burst.’ The amp rating is an important consideration when purchasing an ESC. It is far better to get an ESC capable of more current, at the cost of size or expense, vs. an ESC that might be damaged by too large a current. Larger motors tend to draw more current, and larger propellers, or propellers with a greater pitch will also draw more current. Currently with 4-cell batteries (4S) a 30-amp ESC will suffice for most pilots.
Most drone operators currently use 4S that operate at 16.8 volts. This, however, recently started changing. A few race organizers are encouraging pilots to use higher voltage 5S and 6S batteries. In addition to amperage, ESCs are also rated in their ability to handle voltage. Some ESCs are rated for 3S-4S, while others can handle up to 6S. The power of the motors can be measured in watts, which is voltage multiplied by amps (volts x amps = watts). Therefore, interestingly, as voltage increases, amperage can decrease to keep the total power output of the motor the same. This means that higher voltage batteries can provide the same motor output power at a lower current draw. Alternatively, if the voltage is increased, and the pilot chooses to give a lot more throttle, the amperage will increase and the total power (watts) of the motor will increase and thus the higher voltage drone will fly faster vs a lower voltage drone.
Choosing the right FPV Drone Electronic Speed Controller for your Motor, Propeller and Battery Combination
In selecting an ESC, it is important to think about 3 main considerations. The 3 considerations for ESC choice include:
- Motor size: The size of the motor will greatly dictate the amount of amperage your ESC must be able to handle.
- Propeller: Choice of propeller will also dictate what amp rating your ESC should be. Will your drone be spinning 3, 4, 5, or 6 inch propellers? What kind of performance will you want, and therefore what kind of propeller pitch will you use?
- Battery: Will you be using a 3 cell battery, or a 4, 5 or even 6 cell battery? ESCs are rated for amperage, along with battery cells.
Let’s say for example you are interested in drone racing. Modern racing drones are nearly all using 5 inch propellers with a high pitch. For these high-pitch propellers to spin at high RPM, pilots will select a motor with specifications such as 2207, 2450kv. This motor with an aggressive pitched prop can pull upwards of 40 amps. Therefore, selecting the right ESC is important so that the FETS on the ESC don’t become damaged from the amperage and fail mid-race. Therefore, it is a good idea to design your drone for your specific need and application. Selecting an ESC for voltage, however, is much more straightforward, in that ESCs have ratings on them indicating the battery voltage (S) they can handle. Generally, for a 4S drone running 5 inch propellers, an ESC capable of 30 amp sustained current will work for nearly all applications like freestyle and racing.
FPV Drone Electronic Speed Controller Firmware
ESCs receive a throttle signal from the flight controller. For many years this was a pulse width-modulated signal (PWM) which told the ESC how fast to spin the motor. Modern flight controllers and ESCs however communicate with much faster digital protocols, called D-Shot. The ESC will receive the signal from the flight controller and translate that signal into motor RPM. This change in motor RPM can happen incredibly fast, in part due to the rapid rate of communication between the flight controller and ESC, and also due to the connection between the ESC and the motor. An FPV Drone Electronic Speed Controller utilizes onboard microprocessors and therefore require firmware to control the hardware. This firmware can dictate which protocol your flight controller will use to communicate with your ESC. Depending on the type of ESC you have there are currently a few types of firmware:
- BLHeli: This is found on older 8-bit ESC’s. It is capable of running oneshot protocols. The 8-bit microprocessor of later models, called the F390, is capable of the faster analog signal Multishot.
- BLHeli_S: This is also found on 8-bit ESC’s, but the hardware is more modern, running quieter and able to run all protocols (Oneshot, Multishot) up to D-Shot 600.
- BLHeli_32: This is a relatively new firmware which will run on the new 32-bit ESCs. It is capable of the faster iterations of D-Shot, like D-Shot 1200, and has things like telemetry.
- KISS: This is a proprietary ESC firmware that will only run on KISS ESCs. It is capable of Oneshot and D-Shot, and has telemetry and other features.
This firmware is user-upgradable. Settings on the ESCs can be changed using software available on both Macs and PCs.
The FPV Drone Electronic Speed Controller of years past often came with included electrolytic capacitors. As miniquads became more popular and in attempt to save size and weight, most ESCs no longer come with these large electrolytic capacitors. As flight controller and ESC firmware and hardware became faster, and motors began using more powerful magnets, it became clear that the performance of the drone could be negatively impacted by the lack of a capacitor. Capacitors basically act as a storage tank for electrons, and if placed on the drone near the battery leads it will act to smooth out the power on the drone. Adding a capacitor to the power distribution board (PDB) will help absorb power spikes generated by the brushless motors during braking. In this way, capacitors greatly help protect the electronics, remove electronic noise from the FPV video feed, and can even greatly improve the performance of the drone. Often times a drone may experience some “twitching” especially with powerful motors or certain gyroscopes on the flight controller. Adding a low ESR electrolytic capacitor with a rating of at least 440 µF and 25 volts (v) to the battery leads at the PDB can immediately improve performance. Many pilots use 1000 µF, 35v capacitors and have had great results, even with builds that may twitch.
The FPV Drone Electronic Speed Controller is a crucial component, situated between the flight controller, battery and motor. There are many choices of ESC to meet the needs of many types of drones, from small 2-inch drones, to power-hungry racing drones, to longer range camera drones. It is important to match the ESC with the style of flying and intended application. However, it is better to get an ESC capable of handling greater amps and voltage than you may plan to use, as you may give yourself room to grow, along with a margin of safety.