How to choose a correct FPV Drone ESC for your Drone

Hello Hobby friend:

In this article I will explain what an ESC is, and cover all the basics of ESC used in FPV drones (aka mini quad). Hopefully you will find this an informative guide for beginners getting into FPV or RC in general.

ESC stands for Electronic Speed Controller, and they control the speed of the motors in an FPV drone. The ESC receives throttle signals from the flight controller, and drives the brushless motor at the desired speed. Using good quality ESC's means you should have a reliable and smooth flight experience, though of course, there are other factors to consider.

Current Rating
The first thing to look at when choosing ESC is the current rating, which is measured in Amps. Motors draw current when they spin, if you draw more Amps than your ESC can handle, it will start to overheat and eventually fail. A catastrophic failure can even end up with your ESC in flames! Three things that tend to increase your current draw and put more stress on your ESC:

Higher motor KV
Larger motor size (stator width and height)
Heavier propellers (length and pitch)
There are 2 current ratings to an ESC: continuous and burst. Continuous current rating indicates the maximum amount of continuous current which the ESC can safely handle. Even when racing, it is unlikely that you will use maximum throttle for extended periods, ESC's are usually designed to withstand a higher current for short periods of time (e.g. 10 seconds) and this is the ��burst�� current rating.

Sometimes beginners confuse the current rating of an ESC as amperage that it would apply to the motor, but the opposite is actually the case. The motors that draw current through the ESC's, so the ESC must be rated for the maximum amps of the motor you are using.

How to test your current requirement
You can find out how much current a motor draws by testing it on a thrust stand, along with a power meter. Admittedly that's a lot of hassle, that's why there are many reviewers testing motors for us and publish the results online. Popular sources are:

miniquadtestbench (website)
EngineerX (Youtube)
What you want to look for, is the amp draw of the motor at 100% throttle, spinning the propeller of your choice (or similar size/pitch to the one you plan to use).

See my propeller guide to learn about prop size and pitch.

You can sometimes find this data on the product page but I find 3rd party tests more trustworthy.

It doesn't hurt to leave some margin for error, but there is no need to go overboard. You can use an 30A ESC, or even 40A on something that only draws 20A of current, but it's an overkill.

Thrust and Current Overstated in Thrust Tests
In static conditions, the propeller pushes more air than in flight, so on the bench your motor produces more thrust, with the greater load, it therefore draws more current. When the drone is flying forward (moving through ��free air��), the load is actually smaller, so the amp draw is lower. In addition, the FC always leaves a little throttle headroom to stabilize the copter, so you will never actually see 100% of your motors capability.

Based on my personal experience, maximum amp draw is usually 20% to 30% lower in flight than in static testing.

Battery Limitations
When you draw current from LiPo battery, the voltage sags due to internal resistance. When you reach the discharge limit of the battery, the voltage would sags so much, it can no longer sustain the high current draw.

Learn more about internal resistance of LiPo batteries in this guide.

This is why for most 5�� builds using 4S 1300mAh �C 1500mAh LiPo, 30A ESC are good enough for the most part, because LiPo this size can't sustain 120A of current for very long (a few seconds at best). Most 4S 1500mAh batteries I've tested can't even reach 100A maximum discharge rate.

If you are using larger batteries on a more powerful build, then you should consider higher rating ESC's.

Using Larger ESC's than Required
It's completely okay to use larger ESC's than required, downsides are the extra weight, size and cost. In fact there are advantages with higher current ESC's, which are the lower chance of overheat and higher efficiency.

On an ESC, there are MOSFET (or FET) that basically do all the hard work handling high current. The FET's are bigger and beefier on higher current ESC's, and they don't generate as much heat as the smaller ones, therefore they can be more energy efficient.

Voltage Spikes
Some people prefer using larger ESC's because of voltage spikes which are much higher than the battery voltage. The MOSFET's in larger ESC's usually have a higher voltage tolerance. This is especially popular in 6S builds.

You can also reduce the damage of voltage spikes by soldering extra capacitors in your quad.

ESC Firmware
SimonK and BLHeli
Two of the oldest open source ESC firmware for multirotors are SimonK and BLHeli.

Early ESC's would come with primitive firmware written by manufacturers, so hobbyists tended to flash 3rd party firmware, such as SimonK or BLHeli for better performance. Later, BLHeli became the FPV industry standard and almost all ESC's have it pre-installed.

BLHeli became popular due to its wide range of features and user-friendly interface. For more info about BLHeli and SimonK, here is a discussion comparing the two firmware. Anyway, SimonK has now become obsolete as it's no longer being updated.

BLHeli_S
BLHeli_S firmware is the 2nd generation of the BLHeli firmware, developed specifically for ESC's that have "Busybee" processors. The configurator has a much more simplified user interface. Aikon SEFM 30A and series are early adopters of the updated BLHeli_S firmware.

BLHeli_32
The BLHeli_32 ESC firmware is the third and most recent generation of BLHeli. It's written specifically for 32-bit ESC's and it has gone closed source for this iteration. These more powerful processors allow for better future development, smoother, more precise and reliable performance than previous ESC's.

Which ESC firmware you can install on the ESC, depends on the hardware, more specifically, the processor.

There are many settings in BLHeli_32 and they can be confusing. Discover what the best settings are for an FPV drone in this article.

ESC Processor
The majority of multirotor ESC's on the market use processors (micro-controller or MCU) from ATMEL, Silabs and ARM Cortex. The different MCU's have different spec and features, and are supported by different firmware:

ATMEL 8-bit compatible with both SimonK and BLHeli ESC firmware