Apart from tuning PID, you should also tune BLHeli settings on your ESC to achieve better flight performance with your FPV drone. In this article I will share my BLHeli_32 configurations that I use which give me the best results, and explain what they do.
So, What’s the Best BLHeli Settings?
If you don’t want to read the long article, here is the summary.
Here’s my recommendation right now:
- PWM Frequency:
- Set both LOW and HIGH to 48KHz (you can make up some of the loss of torque by enabling Thrust Linearization in Betaflight later on)
- Alternatively, you can set LOW to 16KHz (or whatever is the lowest) and set HIGH to “by_RPM”, it lets the ESC decide what to use on the go to achieve optimal performance; Try this and 48KHz see which one works better for you
- For racing, try 24KHz on both LOW and HIGH. If it causes vibrations, try 48KHz
- For 2″ or smaller drones like Tiny Whoops, use the highest possible value for both LOW and HIGH (e.g. 48KHz, 96KHz or even 128KHz)
- Motor Timing: 16 deg for responsiveness, Auto for efficiency
- Ramp-up Power: 40%
- ESC Protocol: DShot600 for 8KHz PID Loop Frequency, DShot300 for 4K, DShot125 for 2K
- If you have ESC desync, try to set Demag to High, high Motor Timing, lower Rampup Power
You can flash your ESC to Bluejay (48KHz) firmware, that’s it. 48KHz is better for smoothness and efficiency especially for micro size drones. Some prefer 24KHz because it has slightly more torque and better for prop wash handling, but if you enable thrust linearization in Betaflight on it should make up some of that torque loss when using 48KHz, so you get the best of both worlds.
The original BLHeli_S firmware doesn’t support higher PWM frequency or bi-directional DShot. You need Bluejay firmware which is also required for various features in Betaflight such as RPM filter and Dynamic Idle.
Now let’s go into a bit more detail about what each setting really do.
Motors are driven by a PWM signal from the ESC, which is basically a voltage that turns on and off rapidly.
The “PWM Frequency” setting in BLHeli_32 changes how often the microcontroller (MCU) in the ESC sends updates to the MOSFET. This basically means how often the ESC drives the motor. Note that this “PWM Frequency” setting is entirely unrelated to ESC protocol, FC looptime or the PWM frequency setting in Betaflight.
When you increase the PWM frequency, the motors tend to run smoother and generate less noise, with an increase in efficiency (flight time) and a slight boost in maximum thrust and power. However the downside of higher PWM frequency is the decrease in braking power (just deceleration of the motor, acceleration unaffected) hence results in less responsiveness in flight.
The default value for PWM Frequency in BLHeli_32 is 24KHz. By raising it to 48KHz you should notice an improvement in the smoothness of your flight performance right away. It solves “mid throttle oscillations” in a lot of cases, some even claim their motors come down cooler as well as getting longer flight time thanks to the improved efficiency.
In Jan 2022, the most advanced ESC currently with F4 processors can run up to 128KHz PWM Frequency.
Why does higher PWM Frequency help reduce vibrations?
At lower PWM frequencies, there can be some aliasing/conflicts between the commutation rate and the PWM update rate.
Commutation rate is the time it takes to detect a zero crossing and switch through one feedback cycle, there are 6 commutations per one eRPM, so it is tied directly to RPM
This can result in some odd vibrations or roughness at certain throttle positions. Raising the PWM frequency to the FETs can move the harmonics where this happens outside the range of the commutation rate.
Downsides of Higher PWM Frequency
So why is the default PWM frequency at 24KHz, not higher such as 48KHz? Because there is no free lunch!
Running a higher PWM frequency gives you smoother flying experience at the expense of loss of braking power and responsiveness. Because of this, higher PWM could also reduce peak current draw slightly too, which isn’t necessarily a bad thing for the longevity of the ESC.
At higher PWM Frequency, the torque at low RPM can also be reduced slightly and so your low end throttle might feel softer and less responsive. It can also slightly weaken prop wash handling. When setting PWM frequency too high, the quad tends to be more susceptible to wobbles.
For racers and hardcore freestylers who want to have all the power and responsiveness available, might actually prefer lower PWM frequency such as 24KHz. 48KHz is a good balance between smoothness and responsiveness.
Even better, try Variable PWM Frequency as I explained below, it gives you the best of both worlds.
Variable PWM Frequency by Throttle Position
It makes sense to run maximum PWM frequency some of the times, but not all the times, this is why variable PWM frequency was introduced. This is a feature since BLHeli_32 version 32.8.0, it allows you to set a minimum and maximum PWM frequency, and the ESC linearly increases PWM frequency as throttle goes up.
This gives you the best of both worlds. When your throttle is low, it gives you higher torque and better stability. As you increase throttle it gives you better smoothness and efficiency. The range of PWM frequency allowed depends on your particular ESC. For example with the Tekko32 F3, the minimum and maximum are 48KHz and 96KHz, while some newer F4 ESC allows 24KHz to 128KHz.
You may want to retune PID after enabling this feature.
By setting both low and high to the same value basically disables it and you it becomes a fixed PWM frequency.
Variable PWM Frequency by RPM
Variable PWM Frequency by Throttle Position does not come without problems. First of all, there’s a possibility that the PWM frequency and RPM of the motors can create harmonics which leads to mid throttle oscillations and jello. And at high throttle, the high PWM frequency significantly reduces responsiveness of the drone which might not work well on some setups.
The new Variable PWM Frequency by RPM basically addresses these issues. It tracks the motor RPM so it stays well away from the problematic harmonics in the first place, while using the lowest possible RPM frequency in high throttle to ensure the best possible responsiveness.
Variable PWM Frequency by RPM is a new feature in BLHeli_32 since 32.8.3, probably one of the biggest improvements in ESC performance we have seen in a while, it really improves motor smoothness, torque and braking power.
However, “By RPM” is not necessarily better than “By Throttle Position“, it depends on whether you prefer smoothness and efficiency in high throttle over responsiveness. If you are getting some sort of unexplained mid throttle oscillations, then you might want to give “By RPM” a try.
To enable “By RPM“, you need to flash the latest 32.8.3 firmware (currently in beta and need to be downloaded in github), then simply set PWM Frequency Low to “16KHz” or “24KHz”, and set PWM frequency High to “By RPM”.
Here’s a github thread explaining how it works.
The default Motor Timing in BLHeli_32 is “16 Deg”, which seems to work fine for the majority of builds.
Generally speaking, a higher motor timing is less likely to have “desync” issues, but it reduces both acceleration and braking of the motor, making your drone less responsive. Setting it lower at 8deg also has the same effect, 16deg seems to be the sweet spot.
For most builds, setting motor timing to “16 deg” is recommended. If you are after efficiency and flight time, “Auto” is the best setting.
Regardless of the differences in performance, DShot is indeed more CPU intensive. This has been the reason for some to opt for Multishot, to allow more processing power to run the “ultimate” 32K/32K Gyro sampling and looptime.
Anyway, give both protocols a try if you want to experiment. Personally I feel very minimal difference in performance between the 2 protocols, but when using DShot:
- I don’t have to worry about ESC calibration (calibration doesn’t do anything when running DShot)
- I use ESC beacon which relies on DShot command
- You need DShot in order to use ESC Telemetry
- Betaflight 4.1 recommends DShot300 for RPM Filter when running 4K looptime, or DShot600 for 8K/8K
This setting can help reduce “desync”. Just leave the setting at default unless you have desync issues, otherwise change it to high. (what is ESC desync)
High power builds (e.g. 6S or hexacopters) that suffer from electrical noise may benefit from setting demag to High, but in most cases Medium is fine.
You might experience performance losses by setting it to high, as it’s basically backing down acceleration in order to reduce current spikes and noise.
Rampup Power can be used to reduce current spikes due to the sudden increases in throttle by limiting the change of power, it can be helpful if you have ESC desync issue or excessive electrical noise in your build. It’s previously known as Startup Power in the older BLHeli.
If the motors are pushing close to the limit of your ESC’s, current spikes from punch-outs (sudden wide open throttle) could inflict damage, reducing Rampup Power can lessen this risk.
Leave it at default if you are unsure, but you can tune it and make your quad fly better, but note that setting it too low can lead to slower motor response, and too high can lead to noisier quad and hotter motors.
A slightly higher rampup power can benefit your drone as it pushes the motor harder when it’s trying to gain RPM (faster acceleration), giving you more responsive and powerful feel, but it doesn’t affect braking performance (deceleration). Note that higher rampup power can make your motors run hotter too, so you should keep an eye on motor temperature when increasing it.
If you are suffering from too much vibrations and there is no other solutions, you can try decreasing rampup power. Lowering it incrementally, until you notice a difference in performance, then back off. For most builds it’s hardly noticeable when you lower it to 20% (40% is the default).
On long range builds, you probably want to lower it by a reasonable amount for better efficiency if you don’t need all that motor responsiveness.
Current protection limits the amperage passing through the ESC. The purpose is similar to Rampup Power, but the Current Protection setting is more specific on current limit.
I recommend leaving this setting to off (default), unless you know what you are doing.
Potentially this can be used to protect your ESC from “burning” due to current spikes, crashing and desyncs. But as long as the current rating of your ESC meets the requirement, you shouldn’t need to worry about it.
Dead time in BLHeli is the time interval between each PWM pulse that the ESC will just shut off power to the coil. Dead time is to make sure there’s no overlap when trying to push current to the coil so it can get discharged before the next pulse.
If dead time is too short your motor will get really hot, however if it’s too long it reduces braking torque (especially in higher throttle level), results in less responsive performance.
How about the Rest of the Settings?
For mini quad? Just leave them at default :) A lot of these settings are for fixed wings and planes.
- Jun 2018 – Article created
- Nov 2018 – Added Demag Compensation
- Feb 2019 – Updated Rampup Power and Current Protection
- Jan 2020 – Revised
- May 2021 – Added info regarding new feature, variable PWM Frequency by throttle
- Apr 2022 – Added info about variable PWM Frequency by RPM, and updated best settings thanks to Chris Rosser’s testing