Quick Answer
BLHeli_S is older 8-bit firmware still found on budget ESCs, AM32 is the modern open-source replacement offering better performance and active development, and BLHeli_32 is the most feature-rich 32-bit option with bidirectional DShot. For new builds, AM32 or BLHeli_32 are the way to go.
What Is ESC Firmware and Why Does It Matter?
ESC firmware is the software running on your Electronic Speed Controller that translates flight controller signals into the precise electrical pulses driving each motor. The firmware you choose affects motor response, efficiency, noise levels, and what protocols you can use. It sits between your flight controller and your motors, so even small differences in firmware quality have a noticeable impact on how your drone flies.
Three firmware options dominate the FPV market today: BLHeli_S, AM32, and BLHeli_32. Each has distinct strengths, and choosing the right one depends on your ESC hardware and flying priorities.
BLHeli_S: The Legacy Option
BLHeli_S has been around for years and runs on 8-bit microcontrollers. Most budget ESCs shipped with it until recently, and it still works fine for basic flying. It supports DShot150, DShot300, and DShot600, which covers most use cases.
The main drawbacks are development has effectively stopped, it lacks bidirectional DShot (needed for RPM filtering), and motor response can feel slightly mushy compared to 32-bit alternatives. You will still find BLHeli_S on some BLS (Basic Lite Speed) ESCs from brands like NeutronRC, which use an 8-bit chip to hit lower price points.
AM32: The Open-Source Contender
AM32 (formerly BLHeli_S32) is the open-source successor to BLHeli_S, designed to run on the same low-cost 8-bit hardware while delivering noticeably better performance. It supports all the same protocols as BLHeli_S plus RPM filtering via bidirectional DShot, smoother throttle response, and better motor startup behaviour.
Because AM32 is open-source, it receives regular updates from the community. It is the firmware of choice for budget-to-mid-range ESCs that want 32-bit features without the licensing cost of BLHeli_32. ESCs like the Foxeer Reaper F4 Mini 45A and the NeutronRC Mini 45A ship with AM32 pre-installed.
BLHeli_32: The Full-Featured Standard
BLHeli_32 runs on 32-bit ARM processors and offers the most complete feature set. It supports bidirectional DShot natively, has a graphical configurator, handles higher PWM frequencies, and provides the smoothest motor response of the three. RPM filtering through BLHeli_32 is widely considered the gold standard for noise rejection in Betaflight PID loops.
Most mainstream ESCs from T-Motor, Flycolor, iFlight, and Hobbywing ship with BLHeli_32. The T-Motor Velox V45A Lite V2, Flycolor Trinx G5 60A, and Hobbywing XRotor G2 45A all run BLHeli_32 out of the box.
Which Firmware Should You Choose?
- BLHeli_S only if you have an older ESC that cannot be reflashed. Acceptable for casual flying but you are missing out on RPM filtering.
- AM32 for budget builds where you want modern features without paying for a 32-bit ESC. Great value, actively maintained, and supports RPM filtering.
- BLHeli_32 for any new build where budget allows. The smoothest motor response, best configurator, and widest ESC compatibility. The default choice for most pilots.
What to Buy
- T-Motor Velox V45A Lite V2 - BLHeli_32, reliable 45A for 5-inch builds
- Foxeer Reaper F4 Mini 45A - AM32, compact 20x20 for lightweight builds
- Flycolor Trinx G5 60A - BLHeli_32, 60A for demanding builds
- ESC Collection - Browse all ESC options
FAQ
Q: Can I flash AM32 onto a BLHeli_S ESC?
A: On most 8-bit ESCs, yes. AM32 was specifically designed as a drop-in replacement for BLHeli_S on common chips like the EFM8. Check your ESC's MCU type before flashing. The AM32 configurator makes the process straightforward.
Q: Does BLHeli_32 work with Betaflight RPM filtering?
A: Yes, BLHeli_32 supports bidirectional DShot which enables RPM-based noise filtering in Betaflight. This is one of its biggest advantages over BLHeli_S, giving you cleaner gyro data and allowing more aggressive PID tuning.
Q: Will I notice a difference flying BLHeli_32 vs AM32?
A: For most pilots, the difference is subtle. BLHeli_32 may feel slightly smoother on very aggressive throttle changes, and its configurator is more polished. AM32 is an excellent choice if you are building on a budget and do not want to sacrifice RPM filtering.