In this article we will explain what an ESC is, and the factors that affect your choices. We will look into some of the fundamental factors that beginners should consider when buying ESC’s for a mini quad or racing drone.
ESC stands for Electronic Speed Controller. As the name suggests, they are there to control the speed of the motors. The ESC receives throttle signal from the flight controller, and drives the brushless motor at optimal speed by providing the appropriate level of electrical power. Quality ESC’s ensure a reliable and smooth flight experience.
To find out what ESC options are out there, check out the mini quad parts list.
Index of Content
- Current Rating
- ESC Protocols
- Active Braking and Hardware PWM
- Size and Weight
- Input Voltage
- With or Without BEC
- 4in1 ESC
- ESC Name Brands
- ESC vs Thrust
Current Rating – Amperage
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, your ESC 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. As it is doubtful that you will use maximum throttle for extended periods, even when racing, 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. It is the motors that draw current from the ESC’s, so the ESC must be rated for the maximum Amps of the motor you are using. The fact is there is no benefit to simply using larger ESC’s, e.g. if you replace your 20A ESC’s with some 40A ESC’s you would actually see a drop in performance as your quad will just be heavier.
How to find out about current draw
You can test the current draw of a motor yourself on a thrust stand, with a power meter. Alternatively, there could be thrust test result available online, that gives you the current draw of your choice of motor and propeller combination. Some motor manufacturers even provide this data on their product page.
For example, if you want to use FPVModel 2206 Motor with 5030 propellers on 4S LiPo, it draws 10A at 100% throttle (as shown in my tests), therefore an ESC rated for 12 Amps should be more than enough. If you intend to use 6045 props with this motor however, max current draw could reach 20A, in which case it would be safer to use 20A ESC.
It doesn’t hurt to leave some margin for error, but there is no need to go overboard. You can use 30A or even 40A ESC’s on something that only draws 20A of current, but it’s overkill, adds weight and cost (because bigger ESC are more expensive.
Thrust and Current draw are higher in static tests?
One thing to bear in mind is that most static thrust tests are very likely to show both higher thrust and higher current than can be expected in actual flight conditions. First of all, PID controllers in the FC always tend to leave a little headroom to stabilize the copter, so you will never actually see 100% throttle when in flight. Secondly, the motors won’t need to work as hard when moving forward through “free”air, thus drawing less current.
To verify this theory, I tested it with an OSD (on screen display) that reports the total current draw at all times during the flight. In my test I used DYS Storm 2207 2500KV with DAL Cyclones 5045×3 props. A static thrust test of this motor shows about 30A of current draw at 100% throttle. However in flight the highest sustained current is only about 22-24A.
Besides everyone’s flight style is different, maybe you don’t push full throttle very often, if so your overall current draw will be lower.
SimonK and BLHeli
Two of the oldest ESC firmwares for multirotors are SimonK and BLHeli. Originally these were both open source, developed and maintained by RC hobbyists. In the old days, the firmware written by manufacturers was not optimal, so hobbyists would tend to flash either SimonK or BLHeli onto their ESC’s. Slowly this became the standard for ESC firmware, and most ESC’s came either with BLHeli or SimonK firmware pre-installed.
The majority of the users choose BLHeli because of its range of features and user-friendly interface. For more detailed benefits of BLHeli and SimonK firmware, here is a discussion comparing the two. Anyway, I believe that SimonK has now become obsolete as it’s no longer being updated, so flash BLHeli whenever you can.
BLHeli_S firmware is the 2nd generation of the BLHeli firmware, developed specifically for ESC’s that have Busybee processors with hardware PWM. It also has a much more simplified user interface. Aikon SEFM 30A and DYS XS series are early adopters of the updated BLHeli_S firmware.
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 smoother, more precise and reliable performance than previous ESC’s.
KISS ESC Firmware
The KISS ESC firmware is closed source and is exclusive to KISS ESC.
ATMEL and SILABS
There are three main families of processors (MCU or micro-controller unit) you need to know about for RC Multicopters. Currently the majority of multirotor ESC’s on the market use these processors: Atmel, Silabs and ARM Cortex. The different MCU’s have different spec and features that allow you to run different firmware.
- ATMEL 8-bit based ESC’s are supported by both SimonK and BLHeli ESC firmware
- SILABS 8-bit based ESC can run BLHeli or BLHeli_S only
- Atmel ARM Cortex 32-bit (More specifically STM32 F0) – can run BLHeli_32
ATMEL 8-bit ESC’s used to be more common before the market began to be dominated by SILABS. Silabs ESC’s tend to outperform 8-bit ATMEL ESC’s with the exception of KISS ESC’s. Now in 2017 the Atmel Arm Core MCU is becoming common on 32-bit ESC’s.
SILABS F330 and F39X
Within SiLabs based ESCs there are different processors that provide different performance, for example the 2 main ones currently being F330 and F39X (F390 and F396).
F330 has a lower clock speed, and may have issues running high KV motors. The F39X doesn’t have these problems, and also supports Multishot ESC protocol and Oneshot42 perfectly. Two well known examples are Littlebee 20A (F330) and DYS XM20A (F39X).
Busybee MCU are the upgrade to the F330 and F39X. BLHeli_S ESC’s commonly runs
- BusyBee1 – BB1 (EFM8BB10F8)
- BusyBee2 – BB2 (EFM8BB21F16)
These are better because instead of using software PWM (pulse width modulation), they have specific hardware that can generate a PWM signal that is synced with the duty cycle of the processor, the result is much smoother throttle response. They also support the latest D-Shot ESC protocols. Examples of ESC’s that use these MCU’s would be the Aikon SEFM 30A and DYS XS30A.
In a nutshell, the overall performance ratings from best to worst:
8-bit and 32-bit
Many ESC’s are still using 8-bit processors (F330, F39X, Busybee etc), but since 2016 some 32-bit STM32 based ESC’s started to emerge, such as the KISS 24A Race Edition, the V-Good Firefly, and the Gemfan Maverick. These powerful 32-bit processors unlock many new features that were not possible with the limited processing power and capability of the 8-bit MCU. Features such as the “ESC Telemetry” on the KISS 24A, or “Change Rotation Direction at Start-up” on the Firefly – to mention just a few.
ESC protocols determine how fast the signals can be sent from FC to ESC, which can have a big impact on your quadcopter’s performance. The original (oldest) ESC protocol – standard PWM, has delay up to 2ms, while the currently fastest Multishot has reduced latency down to only about 5-25uS.
Here is a list of current protocols used on quadcopters, from oldest to latest:
Check out this post to learn about ESC firmware and protocols. Not every ESC supports every protocol, make sure you check the specifications before you buy.
Supports for Active Braking and Hardware PWM
There are a few key features in an ESC that make them perform great and are worth mentioning.
- Damped Light, a.k.a. Active Braking – Greatly improves responsiveness
- Hardware PWM – Improves smoothness and responsiveness, makes your quad noticeably quieter and slightly more efficient. It also allows for more fine control
- Dedicated gate driver – Cheaper ESCs use transistors to drive the FET gates, but using a dedicated gate driver improves active braking effectiveness
Size and Weight
Normally the size and weight of an ESC is proportional to the Amp rating.
ESC’s that are designed for mini quad have fairly standard dimensions and weight these days, at around 4-6g each. It’s becoming challenging to make ESC’s any smaller and lighter without sacrificing performance and cooling. For racing you generally want to keep your quad as light as possible, however the ESC is probably not the best place to look if you want to drop more than a few grams.
Smaller ESC’s tend to heat up faster and they can be harder to cool down, which leads to concerns of overheating with tiny ESC’s.
Some ESC’s might support input voltages up to 6S, some might be up to 4S only. Make sure the ESC is compatible with the LiPo voltage you want to use with your mini quad. Ensure you check what the voltage rating is for your ESC’s, powering your ESC with excessively high voltage will fry them, and possibly your motors as well.
Some ESC’s might support input voltages up to 6S, some might only have a 4S maximum. Make sure the ESC is compatible with the LiPo voltage you want to use with your mini quad. Ensure you check what the voltage rating is for your ESC’s, powering your ESC with an excessively high voltage will fry them, and possibly your motors as well.
With or Without BEC – Opto ESC
Some ESC’s come with a built-in BEC (battery eliminate circuit) that outputs 5V (which you can use to power your flight controller, RX and other components). Those that don’t have built-in BEC, are often referred to as “Opto” ESCs by marketers and manufacturers, despite this claim though, these ESC’s might not actually use opto-isolators.
An opto-isolator is an optical component that transfers signals using light. It basically separates the high voltage circuit from the low voltage circuit, and prevents rapidly changing voltages from damaging the ESC electronics or interfering with the signals from the FC.
ESC’s that don’t have a BEC have the advantage of being lighter, smaller, and less noisy (since the motor control circuitry is optically isolated from the radio receiver and flight controller).
Without the 5V BEC however, your FC and RX will require a separate power source. (Note: ESC’s without a BEC don’t have the “red” servo wire, only the signal and ground wires)
Novice Question: Connecting ESC with Motor
I still remember when I started with quadcopters, I was staring at my ESC and motor, wondering how to connect the 3 wires. I still get this question occasionally from beginners.
Don’t worry about the order, simply hook up the three wires on one end of the ESC to the three motor wires in any order you’d like. If the motor spins the wrong direction, simply switch any two of the motor/ESC wires. You can also change the rotation direction setting in BLHeliSuite (if you are using this firmware). For KISS ESC users, there are 2 solder pads you can bridge to reverse motor rotation.
BLHeli ESC Configurator
As you might be aware, BLHeliSuite only runs in Windows, but there is good news for users of other operating systems. There is now a Chrome APP called BLHeli Configurator you can use to flash and configure your ESC’s, which will run on any OS as long as you have Google chrome installed.
(works only with BLHeli and BLHeli_S ESC’s)
ESC Integrated Motors
We have seen motors with an ESC built into them such as the ZTW Black Widow. While it seemed to be convenient and space-saving, it was actually quite a controversial idea. In the case of either the motor or ESC failing, both would need to be replaced, costing more in the long run. Another issue with the motor and ESC in one is that neither can be upgraded individually.
A convenient option is the 4-in-1 ESC, which is basically four ESC’s integrated into one single board of the same size as an FC or PDB, which you can stack together, cleaning up your wiring. However damaging a single ESC means the retirement of the whole board. This is a trade off between risk and convenience.
To combat this compromise, some manufacturers have released a design using 4 separate ESC’s which join together to form a single board which can be built into the stack, such as the Quadrant 4-in-1. A 4-in-1 ESC also has benefits in terms of weight distribution on the aircraft, because the mass is more centralized there is less moment of inertia to the mini quad, which should improve responsiveness.
Name Brands of ESC
Popular, high performance and well-known ESC manufacturers for racing drones (in alphabetic order):
Sorry if I missed anyone, please remind me in the comment.
ESC vs Thrust
Some ESC’s can generate more thrust than others with the same setup (same motor, prop, voltage…). There can be a discrepancy of up to 20% in thrust output between the most and least powerful ESC’s on the market. However that does not indicate the quality of the ESC, which can depend on many other factors: build quality, longevity, supported voltage range, smoothness, electrical noise level, etc… It all depends on what kind of flying you do.
Honestly all the latest ESC’s from the well known brands all have excellent power and perform very similarly, you won’t go wrong to choose among them.
Auto-Timing or Fixed-Timing?
The 2 different approaches to motor timin are auto timing and fixed timing, which are traditionally used in KISS ESC and BLHeli ESC respectively. They have some effect on performance and reliability of the ESC and motor which we discuss in more detail in this article: Motor Timing.
Back in the days when we had multiple different firmware options, bootloader was an important aspect of flashing an ESC. Think of it as a small program you need to install on the ESC, to let you load and access it more easily.
Nowadays we don’t even need to know what bootloader is, since new ESC’s always come with BLHeli firmware and BLHeli bootloader installed already. Users don’t normally need to worry about it. However here is some info for the curious.
Without the bootloader, you can only flash firmware or change ESC config by connecting directly to the processor chip. You can also install the bootloader while flashing firmware this way.
SimonK and BLHeli both have their own bootloaders. BLHeli bootloader offers more features and flexibility, making firmware flashing and configuration much easier. Initially we could flash firmware via the signal lead, using 1-wire interface. More recently “passthrough” became an option, which basically uses the flight controller as the programmer.
Which ESC to Recommend?
Please See our “Top 5 Best” articles to see which ESC we recommend for mini quad.
- Jul 2016 – Article created
- Aug 2017 – updated article with info about BLHeli_32 and 32-bit processors; And thanks to Tom for some of the edits