There are settings you can play with in BLHeli_32 configurator to achieve better performance on your mini quad. In this article I want to share my configurations in BLHeli_32 that have given me the best result.
Basically, this is it!
- PWM Frequency: 48KHz for freestyle; Default value for racing
- Motor Timing: 22 or Auto for freestyle; 25 for racing
- ESC Protocol: DShot1200 if possible, next choice would be Multishot
The setting “PWM Frequency” in BLHeli_32 changes how often the micro controller on the ESC sends updates to the FET’s. In a nutshell, this means how often the ESC drives the motor. The word “PWM” here is unrelated to ESC protocol, FC looptime or the PWM frequency setting in Betaflight.
The default value for PWM Frequency in BLHeli_32 is 24KHz. By raising it to 48KHz should make a noticeable improvement in flight performance for most mini quad’s out there.
When you increase PWM frequency, the motors should run smoother and tend to generate less noise. It solves “mid throttle oscillations” for a lot of people, some even claim their motors come down cooler as well as getting longer flight time thanks to improved efficiency.
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 points. Raising the PWM frequency to the FETs can move the harmonics where this happens outside the range of the commutation rate.
Downside of Higher PWM Frequency
So why is the default not 48KHz? Because there are some drawback to it.
In general higher PWM rates create a smoother response though they can have some small power loss (roughly a few percents). Because of that, it can reduce peak current draw slightly too, which isn’t necessarily a bad thing. And therefore racers might actually prefer lower PWM frequency – (just the default value).
At higher PWM Frequency, the torque at low RPM can also be reduced slightly and so your low end throttle might feel softer.
If you are a perfectionist, you can try 48KHz first, then slowly back it down to find the perfect middle ground between power and smoothness. Every setup is different.
The default Motor Timing in BLHeli_32 is 16, which seems to work just fine for the majority of builds. However I always change it when I am configuring my ESC.
Generally speaking, a higher motor timing is less likely to have “desync” issues. Increasing motor timing also increases the power of your motor in the expense of efficiency.
If you are after blunt power, you can try setting it at around 25, or maybe even slightly higher. However it’s not recommended setting it all the way to the highest just in case of unexpected problems, since every motor is different. High motor timing is also more likely to burn your motors if you crash into something that stops your motors from spinning freely.
For a good balance between power and efficiency, 22 seems to be a good value. For a mini quad, it’s unnecessary to set motor timing any lower, unless you are driving a huge motor that spins 10″ propeller.
The optimal motor timing value can actually change with motor RPM. Therefore you can set motor timing to “Auto”, and it lets the ESC decide what motor timing to use on the fly. Generally speaking, it would give you a good middle ground between efficiency and power through the whole throttle range.
Personally I haven’t seen that big of a difference setting it to auto and 22 in real life. Give it a try anyway and see if it’s any better or worse for your quad and let me know in the comment.
DShot is a newer and more advanced protocol, and it’s recommended over Multishot for several reasons. But the debate of whether DShot or Multishot is better, is still not over! I still occasionally get messages telling me that how Multishot is better and DShot is more noisy and so on.
Regardless the differences in performance, DShot is indeed more CPU intensive. This has been the reason for some to stay with Multishot, so they can make room in 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 am currently quite happy with DShot simply because:
- I don’t have to worry about ESC calibration
- I use ESC beacon which relies on DShot command
- You need DShot in order to use ESC Telemetry
- I only run 8K/8K – sometimes even 8K/4K
- I don’t really notice the differences when I am flying DShot and Multishot
This setting can help reduce the chance of getting a “desync”. Normally you can just leave it at default unless you have desync issues, then you would want to change it to high. But It’s worth knowing that even if you don’t have any desync issues with your quad, it doesn’t seem to do anything if you set it to high.
Rampup Power basically limits the change of power with sudden throttle increase.
Lowering Rampup Power can reduce current spikes that happen when you suddenly increase your throttle. The downside is that if you set it too low, it can lead to slower motor response.
The default should be fine for the most part. I can see it could be useful to decrease Rampup Power when you have some under spec’ed ESC’s and you want to protect them from current spikes that might damage them in a punch out.
This is the limit to what the maximum amount of current is allowed to pass through the ESC.
The purpose of Current Protection is kind of similar to Rampup Power, but this setting allows more fine control on the current.
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.
For mini quad? Just leave them to 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