<p>To clarify, the 48kHz is NOT running on the gyroscope or the FC firmware.
What 48kHz is referring to is the PWM Frequency in the ESC, namely the frequency at which the power MOSFETs on the speed controller switch on and off in order to provide power to the brushless motors and therefore thrust to the craft.
The reason in whoops and small/light craft 3" and smaller will see a flight time improvement is that the RPm ranges these crafts fly at, the switching down-time at lower PWM frequencies means the motor/ESC is having very small active braking events in the switching cycle, then overcompensating by driving higher throttle values to compensate (both of which cost energy).</p>

<p>In some cases, 96kHz will also work very well, although this is often limited to smaller whoop class quads, and I would caution against it on specific instances where the ESC design has a higher dead time value because these tend to suffer failures more often at higher PWM frequency when pushed hard.</p>

CC BY-SA 4.0
2020-04-14T20:21:27.693Z
Thank you for the explanation, that makes sense.
Drones and Whatnot
CC BY-SA 4.0
2020-04-15T01:33:31.970Z
It should also be noted that this ONLY works with micro motors and very high RPMs, and may have minimal or opposite impact on anything larger and heavier than micro drones.
QuadMcFly
CC BY-SA 4.0
2020-04-15T16:52:05.300Z
@QuadMcFly I get why it would have minimal effect on motors with a lower RPM but how would it have a negative impact?
Brecht
CC BY-SA 4.0
2020-04-15T16:56:24.483Z
As mentioned by @tehllama, if the deadtime values are less than ideal, faster PWM rates can create heat in the ESC which is essentially lost energy. It can also cause shoot-through if the deadtime is off, which could burn out the ESC. Unfortunately what we've seen is a lot of manufacturers either miscalculate the deadtime, or have a large enough variation on the quality and specifications of the components used that the appropriate deadtime varies as QC varies.
QuadMcFly
CC BY-SA 4.0
2020-04-15T16:58:01.330Z
With the fairly low current draw and ESCs calibrated for very fast switching on small motors this is low risk, but on larger motors and ESCs it becomes more of an issue.
QuadMcFly
CC BY-SA 4.0
2020-04-15T20:12:15.233Z
QMF - you're correct that it can be an issue on larger setups.  I have successfully ran 48kHz (JESC 2.3) on 2507 and 2408 quads on 7" props, but I have found that the marginal reduction in effective D-Term authority due to reduced active braking torque has put me against a tuning range that is less optimal, and flashing the 24kHz firmware set that tuning window up wider, and the performance is better.  I still maintain that 48kHz does work up to 7" (largest copters I own), even though there aren't any improvements left to be found above 3" or 225g AUW quads.
Tehllama
CC BY-SA 4.0
2020-04-14T20:19:39.227Z
2020-04-21T04:41:31.857Z
2020-04-21T04:41:31.857Z
Tehllama
<p>I was looking at ESC settings for whoops/toothpicks and have seen how the 48KHz JESC firmware can increase flight time. Why is this? Thanks!</p>

CC BY-SA 4.0
2020-04-14T20:18:46.620Z
Welcome!  Increased flight time as compared to what other sampling rate?
Amazon Dies In Darkness
CC BY-SA 4.0
2020-04-14T20:19:58.790Z
Sorry - as opposed to the default rate of 8KHz (as far as I know).
Drones and Whatnot
CC BY-SA 4.0
2020-04-15T01:34:37.877Z
The default on BLHeli 32 is 24khz, and it cannot be changed without custom firmware on BLHeli_S. The non-custom firmware on BLHeli_S runs at 24khz as well.
QuadMcFly
<multirotor>
Why do 48KHz ESCs increase flight time?
Drones and Whatnot
# Why do 48KHz ESCs increase flight time?

(Asked by: username_0 on 2020-04-14)

I was looking at ESC settings for whoops/toothpicks and have seen how the 48KHz JESC firmware can increase flight time. Why is this? Thanks!

**Tags:** multirotor

> **Comments:**
> **username_1**: Welcome!  Increased flight time as compared to what other sampling rate?  
> **username_0**: Sorry - as opposed to the default rate of 8KHz (as far as I know).  
> **username_2**: The default on BLHeli 32 is 24khz, and it cannot be changed without custom firmware on BLHeli_S. The non-custom firmware on BLHeli_S runs at 24khz as well.  

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## 1 answers

### Answer by username_3 on 2020-04-14. Score: 13 | Accepted answer

To clarify, the 48kHz is NOT running on the gyroscope or the FC firmware.
What 48kHz is referring to is the PWM Frequency in the ESC, namely the frequency at which the power MOSFETs on the speed controller switch on and off in order to provide power to the brushless motors and therefore thrust to the craft.
The reason in whoops and small/light craft 3" and smaller will see a flight time improvement is that the RPm ranges these crafts fly at, the switching down-time at lower PWM frequencies means the motor/ESC is having very small active braking events in the switching cycle, then overcompensating by driving higher throttle values to compensate (both of which cost energy).

In some cases, 96kHz will also work very well, although this is often limited to smaller whoop class quads, and I would caution against it on specific instances where the ESC design has a higher dead time value because these tend to suffer failures more often at higher PWM frequency when pushed hard.

> **Comments:**
> **username_0**: Thank you for the explanation, that makes sense.  
> **username_2**: It should also be noted that this ONLY works with micro motors and very high RPMs, and may have minimal or opposite impact on anything larger and heavier than micro username_0.  
> **username_4**: @username_2 I get why it would have minimal effect on motors with a lower RPM but how would it have a negative impact?  
> **username_2**: As mentioned by @username_3, if the deadtime values are less than ideal, faster PWM rates can create heat in the ESC which is essentially lost energy. It can also cause shoot-through if the deadtime is off, which could burn out the ESC. Unfortunately what we've seen is a lot of manufacturers either miscalculate the deadtime, or have a large enough variation on the quality and specifications of the components used that the appropriate deadtime varies as QC varies.  
> **username_2**: With the fairly low current draw and ESCs calibrated for very fast switching on small motors this is low risk, but on larger motors and ESCs it becomes more of an issue.  
> **username_3**: QMF - you're correct that it can be an issue on larger setups.  I have successfully ran 48kHz (JESC 2.3) on 2507 and 2408 quads on 7" props, but I have found that the marginal reduction in effective D-Term authority due to reduced active braking torque has put me against a tuning range that is less optimal, and flashing the 24kHz firmware set that tuning window up wider, and the performance is better.  I still maintain that 48kHz does work up to 7" (largest copters I own), even though there aren't any improvements left to be found above 3" or 225g AUW quads.  

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