In this article we will discuss what ESC is, and factors that affect your choices. We will look into some of the things beginners should know and consider when choosing ESC’s for mini quads (aka racing drones).
ESC stands for Electronic Speed Controller. They takes PWM signal from flight controller, and drives the brushless motor by providing the appropriate level of electrical power.
First thing to look at when choosing ESC is the current rating.
Your motor and propellers draw current when spinning, and your ESC should meet the current requirement. There are 2 current ratings: continuous and burst current. Continuous current rating indicates the maximum amount of current allowed to pass through to the motor constantly and safely. The ESC might allow higher current to pass through for a short period of time (e.g. 10 seconds), and this is the burst current rating.
Some beginners mistaken it as the amount of current that will be applied on the motor, but not really. There is no power gain 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 be heavier.
Knowing Your Current Draw
There are many online resources that you can find out what the current requirement is for your motor propeller setup. Some motor manufacturers even provide this data.
For example, if you want to use FPVModel 2206 Motor with 5030 propellers on 4S LiPo, it will draw 10A at 100% throttle, 12A ESC would be more than enough. But if you intent to use 6045 props on 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 unnecessary weight and cost.
One thing to bear in mind is that most of the static thrust tests we see online normally shows larger numbers than in real flights (both thrust and current). Besides everyone’s flight style is different, maybe you don’t push full throttle very often, then your maximum current draw might be actually 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 and 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 nowadays majority of the ESC’s are SILABS.
SILABS F330 and F39X
Even within SiLabs based ESCs there are different processors of 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 from these problems, and also supports Multishot ESC protocol perfectly (10 times faster than Oneshot125) and Oneshot42. Two famous examples are Littlebee 20A (F330) and DYS XM20A (F39X).
The latest ESC’s with BLHeli_S runs BusyBee1 (EFM8BB10F8) and the BusyBee2 (EFM8BB21F16) MCU’s. These are better because instead of using software PWM they will be using 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.
8-bit and 32-bit
Most ESC’s are still using 8-bit processors (F330, F39X, Busybee etc), but in 2016 we began to see more and more 32-bit STM32 based ESC’s, such as the KISS 24A Race Edition, the V-Good Firefly, and the Gemfan Maverick. The more powerful 32-bit processors unlock many features that were not possible on an 8-bit ESC, such as the “ESC Telemetry” with the KISS 24A, or “Change Rotation Direction at Start-up” with the Firefly.
SimonK and BLHeli
Currently the two of oldest ESC firmware for multirotors are SimonK and BLHeli. These are open source custom firmware. In the old days, firmware written by manufacturers was not optimal, so we had to flash either SimonK or BLHeli on our ESC’s when we bought them. But now most ESC’s come either with BLHeli or SimonK firmware installed because they have become the standard.
Majority of the users choose BLHeli because of the user-friendly interface and rich in features. For more detail benefits of BLHeli and SimonK firmware, here is a nice discussion comparing these firmware.
More recently there is the BLHeli_S firmware developed specifically for ESC’s that have Busybee processors and allow hardware PWM. Only a handful of ESC supports BLHeli_S, such as Aikon SEFM 30A, DYS XS series etc.
There is also KISS ESC firmware which is closed source and only relevant to KISS ESC so we won’t discuss it here.
Maybe not as important now than a year ago (before 2016), another thing related to firmware is bootloader. Think of it as a small program you need to install on the ESC, to let you load and access it more easily.
Nowadays when you buy an ESC with BLHeli pre-flashed, it should come with BLHeli bootloader installed already, so 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. I prefer BLHeli bootloader because it offers more features and flexibility, making firmware flashing and configuration much easier:
- Via the signal lead, using 1-wire interface
- Or via flight controller
Weight and Size
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 if you want to lose a lot of weight.
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 slowest ESC protocol – standard PWM, has delay of about 1ms-2ms, while the currently fastest Multishot, the latency has dropped to only about 5-25uS.
Here is a list of current protocols used on quadcopters, from oldest to latest:
- Standard PWM
- DShot (DShot150, DShot300, DShot600) <== For a comprehensive difference between the above protocols also check out this post
Not all ESC support these protocols though, therefore make sure you consult the datasheet or seller before making the purchase.
Supports for Active Braking and Hardwrae PWM
There are a few key features on an ESC that you should know.
- Damped Light, a.k.a Active Braking – It greatly improves responsiveness
- Hardware PWM – Improves smoothness and responsiveness
- Dedicated gate driver – Cheaper ESCs use transistors to drive the FET gates, but using a dedicated gate driver improves active braking effectiveness
LIPO Battery Support
Depends on what LiPo cell count you want to run on your quad, make sure the ESC of your choice meets the requirement. Majority of the ESC’s support 3S and 4S, but you might want to run 5S or even 6S batteries. Powering your ESC with excessively high voltage will fry your ESC, and possibly your motor.
With BEC 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 even might not 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.
ESC Integrated Motor and 4 in 1 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.
Also check out FlexyFPV’s blog post about ESC.