Understanding ESCs for FPV Drones: How to Choose the Best Electronic Speed Controller

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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 on voltage ratings, current ratings, 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. Using 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 crucial to drone performance as they control the variable speed of motors. They are 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.

ESC Recommendations

I highly recommend opting for a complete FC/ESC stack because it can simplify the building process thanks to its plug-and-play nature. This approach minimizes the need to worry about wiring compatibility between different manufacturers. Check out my recommended flight controller stacks here: https://oscarliang.com/flight-controller/.

If you prefer purchasing your ESCs separately, I offer 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 before connecting.

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ESC Types

There are two main types of ESCs: 4-in-1 ESC and single ESC.

4in1 ESC

A 4-in-1 ESC integrates four individual ESCs onto a single circuit board, each controlling a separate motor. Typically, a 4in1 ESC board is the same size as the flight controller board, 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 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 nowadays are highly 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 inside an FPV drone frame, enhancing the drone’s responsiveness.

Two mounting patterns are available in 4-in-1 ESC boards: 30x30mm and 20x20mm. You should choose one that matches your flight controller for easy installation. However, note that larger ESCs are typically more durable and powerful, thanks to their larger FETs. For 5″ FPV drones or larger, a 30x30mm ESC is the preferred size.

It’s also becoming popular to integrate 4in1 ESC into the flight controller on a single board with 25.5×25.5mm mounting pattern. These boards are designed for smaller FPV drones, specifically 3″ or smaller cinewhoops and ultralight (aka toothpicks) that don’t generally pull a lot of amps.

Single ESC

Single ESCs control only one motor and were more popular in the past, but they have become less common in recent years as the market is dominated by 4in1 ESC.

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. However, this has become less of an advantage since ESCs are generally quite reliable these days and rarely need replacing.

Another advantage is that they get more airflow and have better cooling capabilities since they’re usually mounted on the arms.

When using individual ESCs, they typically need to be connected to a single power distribution board (PDB) or a flight controller with an integrated PDB for easy power supply.

However, individual ESCs do have some drawbacks, such as requiring more soldering and wiring, which can result in a slightly heavier drone due to the added weight of wires and the power distribution board. Additionally, the mass of the ESCs is further away from the center of the drone, which increases the drone’s moment of inertia and potentially reduces its responsiveness.

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How to Choose ESC?

To select the appropriate ESC for your FPV drone, ensure you understand the requirements: the ESC should be compatible with your battery’s voltage and should handle the current draw of your chosen motor and propeller combo at 100% throttle.

Voltage Ratings

Verify that your ESCs support the voltage of your battery. Using a battery voltage that’s too high for your ESC can cause damage. The majority of the ESCs these days support input voltages from a 6S LiPo battery, while some only support up to 4S (or even 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.

Current Ratings

The ESC current rating (or “amp rating”) 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, it’s just a limit, 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 current 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

I will try to explain why I said you don’t have to worry about current ratings in most cases.

For instance, here’s a 55A 4in1 ESC (continuous current rating).

The 55A amp rating is for each motor, which means this 4in1 ESC is able to handle a total current of up to 220A (assuming each motor draws equal amps at 100% throttle). If you’re only pulling 100A in total, each motor is only drawing around 25A, well within the amp limit of 55A. In fact, pulling 100A is a significant load for a 5″ FPV drone, and it’s close to the limit of most LiPo batteries out there, which means they won’t sustain 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 55A-rated ESC to handle bursts of 70A or even 80A for a few seconds. For this reason, 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 50A or 60A during normal use, a higher-rated ESC may still be desirable for its increased robustness. Lower-rated ESCs, such as 30A ones, may be more susceptible to damage during crashes, despite being adequate for typical use. However, beware of the increased weight. If you are building a lightweight drone, you probably want to avoid going overboard.

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ESC Firmware

In this section, I will provide an overview of the most 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 for FPV drones.

BLHeli_S and Bluejay

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 being updated (as development focus shifted to the newer 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, and I highly recommend updating your BLHeli_S ESC with Bluejay for optimal performance. Here’s a comprehensive tutorial on how to flash Bluejay: https://oscarliang.com/bluejay-blheli-s/

BLHeli_32

BLHeli_32 ESC firmware is the third and most recent generation of BLHeli. Designed specifically for 32-bit processor, it has become closed-source in this iteration. While BLHeli_32 ESC offers certain advantages and unique features to the older BLHeli_S, it is considerably more expensive and does not offer significant improvement in performance, therefore many pilots still prefer buying the cheaper BLHeli_S ESC and flash them to Bluejay.

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

AM32 is a relatively new open-source firmware that competes with BLHeli_32. Some new ESCs are already shipped with AM32 firmware. There are pros and cons to AM32 and BLHeli_32, which you can learn about 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 ESC (flashed with Bluejay) and BLHeli_32 ESC 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.

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 prefer value for money.

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ESC Protocols

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 always 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/1.6KHz, use DShot150.
• For 4KHz/3.2KHz, use DShot300.
• For 8KHz, use DShot600.

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How to Connect ESC?

An ESC is powered directly from 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. The order in which you connect the motor wires to the ESC does not matter. Swapping any two of the three wires will simply reverse the motor direction. You can also reverse motor rotation in the ESC settings, saving you from soldering. 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:

Often, you will see a large number of capacitors on an ESC board. These are for noise filtering generated by the motors and FETs. However, 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/.

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ESC Anatomy

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
• MOSFET
• 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.

LDO

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.

Micro Controller

The microcontroller, MCU, or processor is the brain of an ESC, and it’s also where the ESC firmware is stored.

Gate Driver

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.

MOSFET

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/

Current Sensor

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.

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ESC Processor

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 type of FPV drones, for instances, 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.

Conclusion

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.

Edit History

• 2016 – Article created
• 2017 – updated article with info about BLHeli_32 and 32-bit processors
• 2020 – Updated info, added ESC anatomy and connection diagrams, Added info about BLHeli_32 ESC processor
• 2023 – Tutorial revised, updated ESC recommendations
• May 2024 – Updated guide and product links