In this article, we’ll explore the fundamentals of Electronic Speed Controllers (ESCs) and their role in FPV drones. This comprehensive guide aims to provide valuable information such as voltage ratings, current ratings, benefits of different ESC types, and the anatomy of an ESC. Let’s get started!
What is an ESC?
An ESC, or Electronic Speed Controller, is responsible for controlling the speed of motors in an FPV drone. The ESC receives throttle signals from the flight controller and drives the brushless motor at the desired speed. Utilizing high-quality ESCs leads to a reliable and smooth flight experience, although many other factors also play a role in the overall performance.
ESCs are a crucial part of drone performance, as they are responsible for controlling the variable speed of motors. They’re powered by direct current (DC) from your LiPo battery and take motor signals from the flight controller, providing three-phase alternating current to power the motor.
Opting for a complete FC/ESC stack can simplify the building process, as it’s plug-and-play. This approach minimizes the need to worry about wiring compatibility between different manufacturers. Check out my recommended flight controller stacks here: https://oscarliang.com/top-5-best-fc-mini-quad/
For those who prefer to purchase ESCs separately, consider the following recommendations.
When using a 4-in-1 ESC and flight controller from different brands, it’s crucial to verify the pinout before connecting them to prevent potential damage to the components. Always inspect and adjust the wires in the harness as needed prior to connecting.
Top of the Line
Holybro Tekko32 F4 65A
You can get the Tekko32 F4 ESC from these vendors:
- GetFPV: https://oscarliang.com/product-2lkt
- AliExpress: https://s.click.aliexpress.com/e/_DeSQDZX
- RDQ: https://oscarliang.com/product-onoj
- Amazon: https://amzn.to/346eCJh
The Holybro Tekko32 F4 65A is possibly the most robust and lowest noise ESC available, thanks to its impressive onboard noise filtering. You’ll be amazed by the clean power this ESC delivers. Utilizing one of the most powerful F4 processors in ESC, the Tekko32 is rated for 65A with an 85A burst current. It’s an absolute powerhouse for both 4S and 6S freestyle and racing builds. For more details, check out my review: https://oscarliang.com/holybro-kakute-h7-bt-fc-tekko32-f4-50a-65a-esc/
XRotor Micro 60A
You can find the XRotor G2 65A ESC from these vendors:
- AliExpress: https://s.click.aliexpress.com/e/_DlMl6hJ
- RDQ: https://oscarliang.com/product-eczg
- Amazon: https://amzn.to/3TR72b1
- GetFPV: https://oscarliang.com/product-09w6
Purchase the XRotor G2 45A ESC here:
- AliExpress: https://s.click.aliexpress.com/e/_DB9wUEv
The Hobbywing XRotor G2 45A/65A are one of the most recognizable 4in1 ESCs in the industry, endorsed by numerous top pilots. This feature-rich ESC offers DShot and dynamic 120kHz PWM frequency support, robust FETs, direct pins for a low ESR capacitor, and the option to use either a connector for a plug-and-play setup or direct soldering to the flight controller. If budget isn’t a concern, this ESC is a strong contender to consider. Read more here: https://oscarliang.com/hobbywing-xrotor-g2-4in1-esc-45a-65a/
Cheapest Worth Having
SpeedyBee BLHeli_S 50A
You can get the SpeedyBee 50A ESC from these vendors:
- AliExpress: https://s.click.aliexpress.com/e/_DlAHDLb
- Amazon: https://amzn.to/3KieBEn
- GetFPV: https://oscarliang.com/product-hdll
- RDQ: https://oscarliang.com/product-j8vu
- Speedybee: https://oscarliang.com/product-clau
At just over $40, the SpeedyBee BLHeli_S 50A 4in1 is one of the most affordable 4in1 ESCs on the market, offering reliable and decent performance. I’ve personally tested this ESC and have been flying it for over a year. It’s still going strong and performing well. You should seriously consider purchasing this ESC with the SpeedyBee F4 V3 FC as a stack. Together, they cost under $70, making it one of the best value stacks available in 2023. For more details, see my review: https://oscarliang.com/speedybee-f405-v3/
The Best 20x20mm ESC
20x20mm ESCs are smaller and lighter but not as reliable as 30x30mm ESCs due to the larger MOSFETs on the latter. Additionally, soldering is easier on 30x30mm ESCs thanks to larger solder pads. Choose 30x30mm ESCs whenever possible; however, for lightweight racing drones or smaller drones, 20x20mm is a popular option.
Aikon AK32PRO 50A V2
You can get the Aikon AK32PRO 4in1 ESC from these vendors:
- AliExpress: https://s.click.aliexpress.com/e/_DeDfP5P
- RDQ: https://oscarliang.com/product-id38
- GetFPV: https://oscarliang.com/product-o7t9
Despite their compact form factor (20x20mm mounting holes), these ESCs offer performance similar to some 30x30mm boards, with a 50A current rating per motor output and support for up to 6S. They’re small enough to fit in 3″ builds. If you ever need a 20x20mm 4in1 ESC for even a lightweight 5″ build, this is an excellent choice also.
The Best Single ESC
Aikon AK32 35A ESC
You can find the Aikon AK32 35A ESC from these vendors:
- AliExpress: https://s.click.aliexpress.com/e/_DDvLwrJ
- GetFPV: http://bit.ly/2F8TLqh
- Amazon: https://amzn.to/32nKnKK
While I personally prefer 4in1 ESCs due to their ease of use, you may have reasons to choose individual ESCs. In that case, I recommend the AK32 35A ESC by Aikon. I’ve used these ESCs on a build for a couple of years without any issues, and they offer excellent reliability and performance. These are straightforward BLHeli_32 ESCs without fancy RGB LEDs, rated for 2S to 6S voltage, with a burst current rating of up to 45A.
The Types of ESC
There are two main types of ESCs: 4-in-1 ESC and single ESC.
A 4-in-1 ESC integrates four individual ESCs onto a single circuit board, each controlling a separate motor.
Typically, 4in1 ESCs are the same size as the flight controller, which allows for easy stacking and streamlined installation. With fewer solder joints, they require less soldering and wiring. The 4in1 ESC usually sits beneath the flight controller and connects via a single wire harness. However, if one ESC is damaged, you’ll need to replace the entire board—a trade-off between risk and convenience. However, 4in1 ESC these days are very reliable so it’s generally not something to be concerned about.
Additionally, 4-in-1 ESCs offer better weight distribution due to their centralized mass, which can enhance the drone’s responsiveness.
Three 4in1 ESC sizes are available based on mounting patterns for different drone sizes: 30x30mm, 20x20mm, and 16x16mm. Larger ESCs are typically more durable and powerful, thanks to their larger FETs. For 5″ and larger FPV drones, 30x30mm is the most common.
Single ESCs control only one motor and were more popular in the past but have become less common in recent years.
The primary benefit of single ESCs is their ease-of-use and cost-effectiveness when it comes to replacement, as they can be swapped individually if damaged. Since they’re usually mounted on the arms, they receive more airflow and have better cooling capabilities.
When using individual ESCs, they typically need to be connected to a single power distribution board (PDB) or an “AIO flight controller” (a type of flight controller with integrated PDB) for power supply.
However, individual ESCs do have some drawbacks, such as more soldering and wiring, which can also result in a heavier drone due to the added weight of wires and power distribution board.
Determining ESC Requirements
To select the appropriate ESC for your FPV drone, ensure that the ESC is compatible with your battery’s voltage and can handle the current draw of your chosen motor and propeller.
Verify that your ESCs support the voltage of your battery. Using a battery voltage that’s too high for your ESC can cause damage. Some ESCs support input voltages up to 6S, while others only support up to 4S or lower. The terms 6S and 4S refer to the cell count in your LiPo battery. If you’re unfamiliar with these terms, please refer to my LiPo battery beginner guide: https://oscarliang.com/lipo-battery-guide/#Cell-Count
ESC current rating is measured in Amps and is sometimes called “amp rating.” It indicates the maximum current an ESC can handle without damage. Keep in mind that this is not the amount of current pushed to the motors, so don’t worry about it being “too large.” An amp rating can never be too high, only too low.
For the typical FPV drone pilot, the amp rating on most ESCs is more than sufficient. If you are building a specialized racing drone that requires extreme performance or high-speed runs, you will need to pay close attention to the ESC amp rating, along with other factors. However, under normal use, most pilots do not push their batteries hard enough to exceed the current rating of their ESCs.
There are two current ratings for an ESC: continuous and burst. The continuous current rating signifies the constant current the ESC can safely manage, while the burst current rating represents the maximum current the ESC can handle for short periods, typically less than 10 seconds.
Understanding Battery Limitations
If you have a 50A 4in1 ESC (continuous current rating), it should be able to handle 200A of total current for four motors, assuming each motor draws equal amps. If you’re only pulling 100A in total, each motor is drawing around 25A, well within the amp limit of 50A. Pulling 100A is a significant load for a 5″ FPV drone, and it’s close to the limit of LiPo batteries, which means they won’t maintain such high current draw long enough to actually damage your ESC. Additionally, the ESC’s burst limit is typically higher than its continuous current limit, allowing a 50A-rated ESC to handle bursts of 70A or even 80A for a few seconds. Therefore, choosing one of the recommended ESCs on our page should suffice for most 5″ FPV drones without much concern.
Durability and Weight Considerations
Modern ESCs are often marketed with higher amp ratings to indicate increased durability and resistance to voltage spikes. Although your drone may not require 50 or 60 amps during normal use, a higher-rated ESC may still be desirable for its increased robustness. Lower-rated ESCs, such as 30-amp models, may be more susceptible to damage during crashes, despite being adequate for typical use. But beware of the increased weight, if you are building a light weight drone you probably want to avoid going overboard.
Sizing Your ESC
When sizing your ESC, consider the following factors:
- Look for recommendations from experienced pilots who have built similar drones.
- Use higher-rated ESCs if you can afford them, as they tend to be more robust and durable.
- If you are designing a unique drone setup or using an uncommon motor, obtain thrust test data or consult the manufacturer to determine the appropriate ESC amp rating.
In this section, I will provide an overview of the most important and popular ESC firmware. For a complete and up-to-date list of ESC firmware, visit: https://oscarliang.com/esc-firmware-protocols/
SimonK and BLHeli
Two of the oldest open-source ESC firmware for multirotors are SimonK and BLHeli. These are now obsolete and no longer used in modern ESCs, but they deserve an honorable mention for laying the foundation of the FPV drones.
BLHeli_S firmware is the second generation of the BLHeli firmware, developed specifically for ESCs with faster 8-bit “Busybee” processors. This post explains how to connect, flash, and configure BLHeli_S ESCs: https://oscarliang.com/connect-flash-blheli-s-esc/
While the official BLHeli_S firmware is no longer updated (as development shifted to BLHeli_32), custom firmware has emerged to support hardware that comes with BLHeli_S, offering cutting-edge features and performance comparable to the latest and more expensive BLHeli_32 ESCs. A notable example is Bluejay. For a comprehensive tutorial on flashing Bluejay firmware to your BLHeli_S ESC, visit: https://oscarliang.com/bluejay-blheli-s/
BLHeli_32 ESC firmware is the third and most recent generation of BLHeli. Designed specifically for 32-bit hardware, it has become closed-source in this iteration. The more powerful processors allow for smoother, more precise, and reliable performance than previous ESCs. This post explains how to connect, flash, and configure BLHeli_32 ESCs: https://oscarliang.com/connect-flash-blheli-32-esc/
BLHeli_32 has many settings that can be confusing, which I explain here: https://oscarliang.com/best-blheli-32-settings/
AM32 is a relatively new open source firmware that could be the tried-and-true BLHeli_32 alternative. Some latest ESC are already shipped with AM32 firmware. Learn more about AM32 here: https://oscarliang.com/am32-esc-firmware-an-open-source-alternative-to-blheli32/
Which ESC Firmware Should You Choose?
The performance difference between BLHeli_S and BLHeli_32 is minimal, so you can’t go wrong with either option. Both firmware now support Bi-directional DShot, which means you can enable RPM filtering in Betaflight with either type of ESC. Although BLHeli_S ESCs are cheaper, enabling RPM filtering requires flashing third-party firmware (e.g., Bluejay), which involves slightly more work. Meanwhile, BLHeli_32 works out-of-the-box.
BLHeli_32, as the newer generation, offers advanced features that BLHeli_S lacks, such as ESC telemetry and RGB LED support. However, these features do not impact flight performance and are thus not essential. Choose BLHeli_32 if you want a more future-proof ESC, or go for BLHeli_S if you’re on a tight budget.
ESC protocols determine the speed of the motor signal between the FC (flight controller) and the ESC. Here is a list of ESC protocols commonly used in FPV drones, arranged from the oldest to the most recent:
Without delving too deep into technicalities, just know that DShot is currently the standard ESC protocol in FPV drones. You should use DShot in Betaflight for optimal performance. DShot has various speeds, indicated by the number at the end of the names. The speed you choose depends on the PID Loop Frequency set in Betaflight. For 2KHz, use DShot150; for 4KHz, use DShot300; and for 8KHz, use DShot600.
How to Connect ESC?
The ESC is powered directly by a LiPo battery, and the motor speed is controlled by a signal from the flight controller. The motors are connected to the ESC through three wires.
In which order you connect the motor wires to the ESC doesn’t matter, because by swapping any two of the three wires, it will simply reverse the motor direction. You can also reverse motor rotation by configuring the ESC in software. I have a step-by-step guide on how to do that: https://oscarliang.com/change-motor-spin-direction-quadcopter/
Single ESC Wiring:
4in1 ESC Wiring:
Regardless of the amount of filtration available on the ESC, you should always solder an additional capacitor to the power pads of your ESC. This will reduce the chance of getting a noisy FPV feed and improve flight performance. Take a look at this tutorial where I explain why and which capacitors you should use: https://oscarliang.com/capacitors-mini-quad/
Now that we’ve covered ESC types, software, and requirements, let’s discuss the anatomy and components of an ESC. The essential components on an ESC are:
- Microcontroller unit (MCU)
- Gate driver
- Low dropout voltage regulator (LDO)
- Current sensor
- Filtering capacitors
These components work together to control the speed of the motor and ensure efficient operation. I will explain what these components do in more detail below.
A 4in1 ESC basically has four ESCs integrated on the same piece of PCB. These ESCs might share the same components (such as the processor, filtering capacitors, voltage regulators, etc.), making the 4in1 ESC smaller, lighter, and overall more cost-efficient.
A low dropout voltage regulator, or LDO, is a voltage regulator used for converting battery voltage down to an acceptable level to power the microcontroller and other components.
The microcontroller, MCU, or processor is the brain of an ESC, and it’s also where the ESC firmware is stored.
Gate drivers are used to drive the MOSFETs in our ESC. They’re connected to the gate of a MOSFET, hence the name “gate driver.” Older ESCs use simple transistors to drive the MOSFETs. Using dedicated gate drivers improves active braking effectiveness. Instead of having separate gate drivers for the three motor phases, modern BLHeli_32 ESCs use the FD6288 IC chip by Fortior. One of these chips contains three independent MOSFET gate drivers in a single chip.
MOSFETs are like switches; they switch the power on and off thousands of times per second, which is how the motors are driven. Bigger MOSFETs usually mean the ESC can handle higher voltage and current, making the ESC more robust and capable of withstanding abuse. MOSFET size is especially important for high voltage rigs, such as 6S, due to the higher voltage spikes.
I have a tutorial explaining how MOSFET work: https://oscarliang.com/how-to-use-mosfet-beginner-tutorial/
The current sensor measures the current that goes through the ESC and sends that information to the flight controller. This is helpful as you can display the drone’s current draw on screen in real time and see how much battery capacity has been consumed.
Multirotor ESCs on the market primarily use microcontroller from ATMEL, Silabs, and ARM Cortex. Each type of MCU has unique specifications, features, and firmware support:
- ATMEL 8-bit: Compatible with both SimonK and BLHeli ESC firmware
- SILABS 8-bit: Supported by BLHeli or BLHeli_S
- ARM Cortex 32-bit (e.g., STM32 F0, F3, L4): Can run BLHeli_32
ATMEL 8-bit ESCs running SimonK were more common until Silabs-based ESCs gained popularity due to the rise of BLHeli_S. In 2016, 32-bit ARM Core MCUs were introduced to ESCs, running BLHeli_32 firmware.
BLHeli_32 ESC Processors
BLHeli_32 ESCs use STM32 processors, similar to those found in flight controllers. The common processors used in ESCs are F0, F3, and F4.
Manufacturers started using more powerful F3 and F4 MCUs on BLHeli_32 ESCs since 2021, primarily due to the global chip shortage, not for their processing power. These more powerful ESCs don’t offer significant benefits over the original BLHeli_32 ESCs based on the F0 processor or older BLHeli_S ESCs (non-STM32 MCUs). The high PWM frequency (e.g., 128kHz) offered by these faster processors is mainly useful for certain aircraft, like cinematic flying and micro drones, where smoother motors and better efficiency are desired. This high PWM frequency doesn’t provide optimal acceleration and torque at low RPM for powerful and fast FPV drones.
To take full advantage of “variable PWM frequency by RPM” feature in BLHeli_32, smaller aircraft can benefit from the higher PWM frequency of the faster F4 processor (up to 128KHz) because they typically have much higher RPM and higher-frequency harmonics. For larger drones, such as 5″, the RPM is lower, and 96KHz or even 48KHz should suffice, making higher PWM frequency less important.
SILABS F330 and F39X Processors
These processors are used in BLHeli_S ESCs.
SiLabs-based ESCs feature various processors with different performance levels, such as the F330 and F39X (F390/F396).
The F330 has a lower clock speed than the F39X and may struggle with high KV motors. The F39X doesn’t have these issues and supports Multishot ESC protocol and Oneshot42 seamlessly. Well-known examples include the Littlebee 20A (F330) and DYS XM20A (F39X).
Busybee (EFM8BB) Processors
These are BLHeli_S ESC Processors.
Busybee MCUs are an upgrade to the F330 and F39X. If you currently have a BLHeli_S ESC, it probably uses a BusyBee chip. There are two BusyBee chips:
- BusyBee1 – EFM8BB10F8 (aka BB1)
- BusyBee2 – EFM8BB21F16 (aka BB2)
Rather than using software PWM (pulse width modulation), Busybee MCUs have dedicated hardware for generating a PWM signal synced with the processor’s duty cycle, resulting in smoother throttle response. They also support DShot ESC Protocol, making them a cost-effective and efficient solution for today’s standards
Examples of ESCs that use these MCUs include the Aikon SEFM 30A and DYS XS30A.
The overall performance ratings within 8-bit processors are (from the best to the worst): BB2 > BB1 > F39X > F330 > Atmel-8-bit.
Armed with the essential information about ESC types, electrical ratings, protocols, and anatomy, you’re well-prepared to select the perfect ESC for your FPV drone build. Keep in mind that the majority of the latest ESCs on the market perform at a similar level, making it challenging to go wrong with any of the options mentioned in this tutorial. Focus on understanding your specific needs and preferences to find the best match for your build.
- Jul 2016 – Article created
- Aug 2017 – updated article with info about BLHeli_32 and 32-bit processors
- Feb 2020 – Updated info, added ESC anatomy and connection diagrams
- Apr 2022 – Added info about BLHeli_32 ESC processor
- Mar 2023 – Tutorial revised, updated ESC recommendations