Electronic Speed Controller (ESC) for Drones and UAVs

How to choose ESC for drones?

Using a good quality ESC means you should have a reliable and smooth flying experience, but of course, there are other factors to consider. Here's a guide on how to choose the best ESC for quadcopter and FPV drones：

1. ESC current rating

When you choose an ESC for UAVs, the first thing to consider is the current rating, which is the amount of current it can handle. The ESC is measured in Amps, therefore sometimes referred to as amp rating.

It is recommended that you decide on the current rating of the ESC after you have selected the proper motor size. Because the motor draws current as it spins, and if your ESC handles too much current, it will begin to overheat and eventually break down.

In general, the ESC should be rated 10-20% higher than the motor's maximum current at 100% throttle. For example, if your motor produces 10A at full throttle, you should use a 12A or 15A ESC.

For safety reasons, you can also choose some ESCs that are equipped with temperature sensors. These sensors not only monitor their temperature and adjust to prevent overheating, but also prevent damage if your drone hits something sharp or flies too close to an object with high thermal conductivity.

2. Input voltage rating

In addition to the amperage, ESCs have a maximum amount of voltage that they support, which is the voltage rating. Some ESCs are rated for 3S-4S, while others can handle up to 6S. It largely depends on what battery voltage you want to run on your drone, too high a voltage used to power your ESC will destroy both the ESC and the motor.

The power of a motor can be measured in watts, which is voltage multiplied by amperage (volts x amps = watts). Therefore, as the voltage increases, the amperage may decrease to keep the engine's total power equal. This means that a higher voltage battery can provide the same engine output power at a lower current draw.

Moreover, when the voltage of the ESC is increased, the pilot will tend to choose to give more throttle. This increases the amperage and the total power (watts) of the motor increases. This is why a high-voltage drone will fly faster compared to a low-voltage drone.

3. Weight and size

Typically, the weight and size of an ESC are determined by its current rating and are proportional to it. Most ESCs on the market today are similar in size and weight, with single ESCs weighing between 4-6 grams and quad ESCs weighing around 12 grams to 15 grams.

Lighter ESCs are better suited for racing drones, they allow the drone to have a faster spin and deceleration and produce a faster speed change. But the lighter the ESC, the lower the heat dissipation, raising concerns about overheating.

4. ESC firmware

As the software that runs on each ESC, the ESC firmware provides information about the protocols and configuration interfaces it supports and determines the performance of the ESC. Most ESCs are running the following 3 types of ESC firmware.

• BLHeli_S firmware is the second generation after BLHeli, developed for the BusyBee processors (BB1 & BB2 chips). Thanks to the hardware PWM, BLHeli_S delivers a smoother and more responsive motor response than previously. It uses damped light (Regenerative Breaking) for better drone control. Besides, BLHeli_S Supports regular 1-2ms input signal, as well as Oneshot125, Oneshot42, and Multishot.

• BLHeli_32 ESC firmware is the 3rd generation of BLHeli's firmware, which is specially written for ESCs that utilize 32-bit MCU (Microcontroller Unit). BLHeli_32 has higher processing power, making it possible to have faster, lower latency, and higher update rates for input signals such as the Dshot1200. However, you need to pay a license fee to the developer and the source code is closed.

• BLHeli is an outdated open-source firmware, so it is currently only used by a small number of aircraft ESCs.

• KISS is a closed-source ESC, which means that the KISS firmware is exclusive to KISS ESCs.

5. With or without BEC

Another important thing you may want to know before buying an ESC is what BEC means and do you need it. BEC stands for Battery Elimination Circuit. An ESC with a BEC can power devices on the flight platform such as a receiver, rudder, or flight controller.

Whether you need a BEC or not depends on your flight controller. Most drones now have a separate power module to power the flight controller, in which case you will not need an ESC with a BEC. For example, JOUAV's CW-40 VTOL drone has batteries designed to power the flight controller, payload, and engine electric start. However, if you want or need to power other devices such as servos and receivers, then an ESC with BEC will be necessary, which will allow you to get rid of the extra receiver battery pack.

Tips for choosing an ESC with BEC

There are two main types of BECs: switched and linear (sometimes called "LDO"). Which type you choose depends on your budget. The linear BEC is the cheapest and most common type of BEC, but it runs with only 25% of the power used for useful work and 75% of the power is converted to heat. The switched BEC is more efficient but more expensive. In practice, the highest efficiency of switched BEC is about 85%, with only about 15% being converted to heat.

Also, you must double-check the current limits of their BECs and make sure that the total current of all servos/receivers, etc. does not exceed this amount. In general, for small models, 1.5 to 2 amps is sufficient; for medium-sized models, 3 amp types need to be considered. For large models, the BEC must provide 5A or more.

6. ESC protocols

ESC protocols are the "language" in which the flight controller and ESC talk and determine how fast the signal is sent from the FC to the ESC. Here are all the ESC protocols currently available for UAVs and how long it takes them to send a packet.

• Standard PWM (1000

  us – 2000us)

• Oneshot125 (125us – 250us)

• Oneshot 42 (42us – 84us)

• Multishot (5us – 25us)

• Dshot

  • Dshot150 (106.8us)

  • Dshot300 (53.4us)

  • Dshot600 (26.7us)

  • DShot1200

    (13.4us)

• ProShot

Standard PWM (1000us – 2000us)

PWM means "pulse width modulation" and it uses pulse timing to determine the speed at which the motor should rotate. Almost all ESCs support the PWM protocol, which is how radio receivers communicated with ESCs and servos long before the advent of drones. But this ancient protocol has a low refresh rate and is only suitable for large, slow-flying drones.

Oneshot125 (125us – 250us) and Oneshot 42 (42us – 84us)

Oneshot 125 and Oneshot 42 are both analog protocols introduced by the BLHeli firmware. They work very similarly to the PWM protocol, but they have a higher refresh rate and faster communication speed.

On OneShot 125, the duration of each packet is between 125 and 250 microseconds, while on OneShot 42, the duration of the packet is between 42 and 84 microseconds. So, Oneshot 125 is 4 times faster than PWM and OneShot 42 is almost 10 times faster than PWM.

However, since some processors with BLHeli ESCs are not enough, they can only work with OneShot 125 and do not support OneShot 42.

Multishot (5us – 25us)

Multishot is another analog protocol similar to PWM introduced by BLHeli firmware, but with a much higher refresh rate. the duration of each packet of Multishot is between 5 and 25 microseconds, which is 20 times faster than PWM.

However, Multishot requires a very fast communication speed, which is only supported by BLHeli ESCs with super-fast microcontrollers. On top of that, the protocol is susceptible to electromagnetic interference from motors or other devices, so it also requires high-quality wiring and some insulation to avoid synchronization problems.

Dshot (13.4us-106.8us)

We recommend the DShot ESC protocol for better reliability and performance. It can send not only motor speed but also specific commands to the ESC. Directional DShot is also possible, which means that the ESC and FC can communicate in both directions and the ESC can send motor speed data back to the FC. This makes speed filtering and other advanced PID functions such as dynamic idling possible.

• Dshot150 (106.8us)

• Dshot300 (53.4us)

• Dshot600 (26.7us)

• DShot1200 (13.4us)

Between DShot300/600/1200, the faster protocol is better in terms of latency. But not necessarily, the faster protocols may be more prone to corrupted packets. It is recommended that the appropriate DShot speed be chosen based on the PID loop frequency.

• 2K PID loop frequency with DShot 150

• 4K PID loop frequency with DShot300

• 8K PID loop frequency with DShot600

ProShot

ProShot is the latest ESC protocol that encodes 16-bit DShot into 4 PWM pulses. ProShot shares the same throttle resolution, frame structure, CRC, etc. as DShot. Unlike DShot, ProShot only sends 4 pulses per signal instead of 16 pulses. The wider pulses allow ProShot's microcontroller to read without DMA, allowing a wider range of MCU work. Due to the shorter signal width, Proshot has lower CPU utilization and higher update rates than DShot.

However, the PWM pulses in ProShot can be more prone to noise. Though filtering capacitors can be installed on the signal line to reduce noise, unfortunately, using filtering capacitors at high update rates can scramble the signal, so it is not suitable for high-speed development.

ESC processors

There are three main families of processors (MCUs or microcontrollers) that you need to know about multiplexing. Most of the ESC multiplexers on the market today use these processors: Atmel, Silabs e ARM Cortex. They have different specifications and features that allow you to run different firmware.

• ATMEL's 8-bit supports SimonK firmware and BLHeli ESC firmware

• SILABS' 8-bit can only execute BLHeli or BLHeli_S

• Atmel ARM Cortex 32-bit (especially STM32 F0) - can execute BLHeli_32

ATMEL's 8-bit ESCs were more common until the market started to be dominated by Silabs. Except for the KISS ESC, Silabs ESCs tended to outperform ATMEL's 8-bit. Starting in 2017, the MCU Atmel ARM Core has become the common processor for ESC 32-bit.

7. Capacitor

A typical 5 FPV drone draws between 150-190 A at full throttle. This huge current draw strains the battery and causes what is called a voltage spike. If the spike is too strong or occurs for a longer period, voltage regulators, capacitors, and field effect tubes can be damaged and fail.

Capacitors can help protect electronics by absorbing the energy of these spikes before they penetrate your drone and cause damage. In addition to this, capacitors eliminate electronic noise in FPV video signals and can also greatly improve the performance of your drone.

The most commonly used capacitor is the low-ESR capacitor. Adding a low-ESR electrolytic capacitor with a nominal value of at least 440 μF at 25 volts (v) PDB to the battery's cable can immediately improve performance.

8. 4-in-1 or individual ESC

There are two types of electronic speed controllers for drones, 4-in-1 ESCs or individual ESCs. The 4-in-1 ESC is all 4 ESCs combined on a single printed circuit board and mounted in the main stack underneath the flight controller. Usually, they come with a voltage regulator and can also be used as a power distribution board (PDB).

As for usage, there is no difference between the 4-in-1 ESC and the separate ESC. the 4-in-1 ESC offers a lighter and cleaner look to the drone, so it is more popular than the individual ESC.

The only downside to the 4-in-1 ESC is that if you, unfortunately, damage one ESC, it means the whole ESC is useless. If you are a beginner and have a small budget, we recommend you expand the ESC separately as it is cheaper and more economical to replace and repair.