There are settings you can play with in BLHeli_32 configurator to achieve better flight performance on 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 (or higher) for racing
- Motor Timing: 22 or Auto for freestyle; 25 (or higher) for racing
- ESC Protocol: DShot1200 or Multishot
The setting “PWM Frequency” in BLHeli_32 changes how often the micro controller in the ESC sends updates to the MOSFET. In a nutshell, this basically 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 – especially smoothness.
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 the improved efficiency.
Don’t go below 24kHz, you should always choose between 24 and 48KHz.
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 not 48KHz then? Well, because there is no free lunch!
Higher PWM frequency gives you smoother flying experience in the expense of some small power loss (roughly a few percent). Because of this, it can reduce peak current draw slightly too, which isn’t necessarily a bad thing.
At higher PWM Frequency, the torque at low RPM can also be reduced slightly and so your low end throttle might feel softer.
For racers who want to have all the power available, might actually prefer lower PWM frequency, or just stick with the default value.
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 Deg”, which seems to work just fine for the majority of builds. However I always increase 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 I don’t recommend setting it all the way to the highest just in case of unexpected problems, since every motor is different. Motor timing that is too high tends to cause hot motors, and 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 to get started. For a mini quad, it’s unnecessary to set motor timing lower than the default, unless you are driving a huge motor that spins 10″ propeller.
The optimal motor timing value can actually change with motor RPM, therefore you are given the option “Auto” too. 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 on 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 for 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.
Some 6S builds, or builds with lots of electrical noise, can benefit from demag High, but generally you should just leave it at medium.
Rampup Power limits the change of power when you suddenly increase throttle, and reduces the current spikes. 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. It could be useful if you have some under-spec’ed ESC’s, you can reduce Rampup Power to to protect them from current spikes that might damage them in punch-outs.
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 amount of 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.
How about the Rest of the Settings?
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