In this article we will explain what ESC is, and the factors that affect your choices. We will look into some of the fundamental considerations that beginners should know when buying ESC’s for mini quads (aka racing drones).
ESC stands for Electronic Speed Controller. As the name suggests, they are there to control the speed of the motors. They receive signal/command from flight controller, and drives the brushless motor by providing the appropriate level of electrical power in order to change motor speed (RPM). Quality ESC’s ensure 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
First thing to look at when choosing ESC is the power rating, which is measured in amps (current rating).
Motor draws current when they spin. If you draw more current than it can handle, your ESC will start to overheat and eventually burns out or even go up in flames. There are 2 current ratings: continuous and burst current. Continuous current rating indicates the maximum amount of constant current allowed to pass through to the motor safely. The ESC might allow a higher current to pass through for a short period of time (e.g. 10 seconds), and this is the burst current rating.
Some beginners confuse current rating as the amount of current that would be applied on the motor, but No. The fact is there will be no power gain to your motors using larger ESC’s, e.g. using 40A ESC doesn’t mean your quadcopter is going to fly faster than using 20A ESC, instead your quad will just be heavier.
How to find out about current draw
You can test it yourself on a thrust stand, with a power meter. Alternatively, there are many thrust tests available online you can check the current draw of your motor and propeller setup. 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), 12A ESC should be more than enough. But if you intent to use 6045 props with this motor, 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 no need to go crazy on it. You can use 30A ESC or even 40A ESCs on something that only draw 20A of current. It will work fine, but it’s an overkill and dead weight and extra cost (bigger ESC costs more).
Current draw is higher in thrust test?
One thing to bear in mind is that most of the static thrust tests we see online is very likely to be showing bigger numbers than what you would get in real flights (both thrust and current). First of all, PID controllers in the FC always tend to leave a little headroom to stabilize the copter. Secondly, the motors won’t need to work as hard to spin at 100% when move fast forward through the air, thus drawing less current.
To verify this theory, I tested it with an OSD that reports the total current draw at all time during flight. I tried DYS Storm 2207 2500KV with DAL Cyclones 5045×3 props. In static thrust test, it says it should pull about 30A of current at 100% throttle. However the highest sustained current is only about 85A-90A, so that’s only 22-24A per motor.
Besides everyone’s flight style is different, maybe you don’t push full throttle very often, then your maximum current draw will be lower.
ATMEL and SILABS
There are two main families of micro processors you need to know about RC Multicopters:
Currently majority of the multirotors ESC’s on the market use micro processors from 2 brands: ATMEL, Silabs. The different MCU’s have different spec, and allows you to run different firmware.
- ATMEL based ESC’s are supported by both SimonK and BLHeli ESC firmware
- SILABS based ESC can run BLHeli only
ATMEL MCU used to be more common, but the market of ESC is being taken over by SILABS. Silabs ESC’s tend to outperform 8-bit ATMEL ESC’s with the exception of KISS 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 is lower in clock speed, and may have issues running high KV motors. 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).
The latest ESC’s with BLHeli_S runs BusyBee1 – BB1 (EFM8BB10F8) and the BusyBee2 – BB2 (EFM8BB21F16) MCU’s. These are better because instead of using software PWM, these new MCU uses hardware PWM that is synced to duty cycle. They also support the latest D-Shot ESC protocols. Examples ESC’s that use these MCU would be the Aikon SEFM 30A and DYS XS30A.
Basically BB2 > BB1 > F39X > F330 > Atmel in overall performance.
8-bit and 32-bit
Most ESC’s are still using 8-bit processors (F330, F39X, Busybee etc), but in 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. The powerful 32-bit processors unlock many new features that were not possible previously on an 8-bit ESC, such as the “ESC Telemetry” on the KISS 24A, or “Change Rotation Direction at Start-up” on the Firefly.
SimonK and BLHeli
Two of oldest ESC firmware for multirotors are SimonK and BLHeli. These are open source firmware developed by RC hobbyists. In the old days, firmware written by manufacturers was not optimal, so hobbyists would tend to flash either SimonK or BLHeli on their ESC’s. Slowly these firmware became the standard of ESC firmware, and most ESC’s came either with BLHeli or SimonK firmware installed.
Majority of the users choose BLHeli because of the user-friendly interface and rich in features. For more detailed benefits of BLHeli and SimonK firmware, here is a nice discussion comparing these firmware. Anyway, I believe SimonK has become obsolete as it’s not being updated anymore, so the general advice is you should run when you see ESC being sold comes with SimonK. :)
BLHeli_S firmware is the 2nd generation of the BLHeli firmware, developed specifically for ESC’s that have Busybee processors and allow hardware PWM. It also has a much simplified user interface. Aikon SEFM 30A and DYS XS series are the early adopter of BLHeli_S.
The BLHeli_32 ESC firmware is the third generation of BLHeli. It’s written specifically for 32-bit ESC and it has gone closed source in this version. The more powerful processor would allow 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.
ESC protocols determine how fast the signals can be sent from FC to ESC, which will have some pretty 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:
Not every ESC supports these protocols, make sure you check.
Supports for Active Braking and Hardwrae PWM
There are a few key features in an ESC that are worth considering.
- Damped Light, a.k.a Active Braking – It greatly improves responsiveness
- Hardware PWM – Improves smoothness and responsiveness, make your quad noticeably quieter and slightly more efficient. It also allows 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
ESC designed for mini quad have fairly standard dimension and weight these days, around 4-6g each. For racing you generally want to keep your quad as light as possible, but ESC is probably not the best place to look at if you want to lose a lot of weight.
Smaller ESC also means heat builds up quicker and harder to cool down, so there is concerns of over heating with tiny ESC’s.
Some ESC might support up to 6S, some might do 4S. Make sure the ESC is compatible with the LiPo voltage you want to run in the mini quad. Majority of the ESC’s nowadays support up to at least 4S Lipo cell count. Powering your ESC with excessively high voltage will fry your ESC’s, and possibly your motors as well.
With or Without BEC – Opto ESC
Some ESC’s come with built-in BEC that outputs 5V (which you can use for flight controller and radio receiver). Those don’t, are often referred to as “Opto” ESCs by marketers and manufacturers, despite these ESC’s might not really have opto-isolators.
Opto isolator is an optical component in an ESC that transfers the signal using light. It basically separates the high voltage circuit from the low voltage circuit, and prevents rapid changing voltages from damaging the ESC electronics or interfering the signal.
ESC that doesn’t have BEC has the advantage of being lighter, smaller, and less noisy (since the motor control circuitry is optically isolated from the radio receiver and flight controller).
However without the 5V BEC, means it requires a separate power source for the FC and RX. (Notice it doesn’t have the “red” servo wire, only signal and ground)
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 and doesn’t support other OS. Good news is for BLHeli and BLHeli_S ESC, there is now a Chrome APP called BLHeli Configurator for ESC flash and configure. You can run it on any OS as long as you have Google chrome installed.
ESC Integrated Motor and 4in1 ESC
It might or might not be a good idea to use motors with built-in ESC’s, such as the ZTW Black Widow. It seems to be convenient and space-saving,. But if either the motor or ESC fails, both need to be replaced which is more expensive. Also you can’t upgrade just the motor or ESC individually but both.
Another convenient option is the 4-in-1 ESC. Four ESC’s are integrated into one board of size of a FC or PDB, which cleans up your wiring a lot. However 1 damaged ESC means the retirement of the whole board. A trade off between risk and convenience.
4in1 ESC has benefit in terms of weight distribution of the aircraft. Mass is more centralized meaning there is less moment of inertia to the mini quad.
Name Brands of ESC
Popular, high performance and well-known ESC manufacturers are 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 power and thrust than others with the same setup (same motor, prop, battery, voltage…). There are some 20% variance in thrust output between the most and least powerful ESC on the market. However that does not indicate the quality of the ESC, which depends 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.
But to be honest, the latest ESC from the name brands all have excellent power and perform very similarly, and you won’t go wrong to choose among them.
Auto-Timing or Fixed-Timing?
The 2 different approach to motor timing: auto timing and fixed timing are traditionally used in KISS ESC and BLHeli ESC respective. They have some effect on performance and reliability of the ESC and motor which we discussed in more detail in this article: Motor Timing.
Back in the days when we had multiple different firmware on the market, bootloader was an important aspect of flashing 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 in case someone is curious.
Without the bootloader, you can only flash firmware or change ESC config by connecting directly to the processor chip, (or to the flashing soldering pad provided if available). While flashing firmware this way, you can also install the bootloader.
SimonK and BLHeli both have their own bootloaders. BLHeli bootloader offers more features and flexibility, making firmware flashing and configuration much easier. At first we could do that via the signal lead, using 1-wire interface, later on we can even do “passthrough” basically using flight controller as a programmer.
Which ESC to Recommend?
Please See our “Top 5 Best” articles to see which ESC we recommend for mini quad.