Longer flight times on your micro

Thanks to Joe Lucid, the creator of JESC there is now a new BLHELI_S version that allows for up to 30% more flight time. The smaller your quad the bigger the improvement, so this is definitely something that all whoop and toothpick pilots should look into.

The good news ist, that this improvement is available for free, you do not need a JESC license, although I highly recommend getting one, so you can enable RPM filtering on your BLHELI_S ESC.


In order to get this update you have to meet two prerequisites:

  1. Make sure you have BetaFlight 4.1.x installed on your flight controller
  2. Make sure your ESC’s do support JESC - your AIO flight-controller must have the better (BB21) ESC MCU’s

Flashing JESC

After installing and configuring at least BetaFlight 4.1.x follow the steps shown below to install JESC:

  1. download the JESC Configurator and start it
  2. Connect your flight-controller to your computer via USB
  3. Plug in the battery to your quadcopter (make sure to remove your props before attaching your battery)
  4. Connect the JESC configurator to your flight-controller by clicking the “Connect” button on the top right
  5. Click the “Read Setup” button on the bottom right
  6. Make sure that the currently flashed version has an H in the version number - this means you can flash JESC now
  7. Click the “Flash All” button. From the dropdown select JESC 2.2 - 48kHz (early access). The version you will see here might be different, just make sure you select the 48kHz version
  8. Hit “Flash” and lean back - this will take a minute or two
  9. You should now see the new version being flashed on all ESC’s. Double check, that you indeed flashed ALL ESC’s

That is it - depending on your build you can now enjoy up to 30% more flight times.

I also have an article on installing ESC telemetry and configuring RPM filters on BLHELI_S ESC’s.


But how?

The really interesting question is, how does it work and what is the trade-off? The smaller the motor the smaller it’s inductance (and thus it’s capability to hold current when the applied voltage changes). On smaller motors and 24kHz the current does not just decrease in the off phase but might change direction and thus basically slow down the motor. This basically means that the motor is accelerating and slowing down in each PWM cycle, which wastes a lot of energy.

48kHz on the other hand decreases the time the motor has to slow down, thus wasting less energy. To understand the trade off we have to take the ECS’s deadtime into account: the deadtime is given in 24.5ns units. When we now have a look at for example the NamelessRC AIO ESC’s which needs a deadtime of 120, corresponding to 20.4ns x 120 = 2448 or ~2.5us. This means that the deadtime takes around 12% of an 48kHz PWM cycle (which takes 1/48000 = ~20.8us).

2.5 / 20.8 x 100 = ~12

On the other hand, switching also takes energy, so since we switch with double the speed, we use double the energy for switching - this means in some cases we use more energy than we safe. Generally speaking the benefits are the highest on small motors (<=080x) and ESC’s with a low deadtime - preferably a deadtime of 5.

Faster switching also reduces noise, which can be of benefit especially on bigger rigs.

CONCLUSION: Your mileage may vary. Try it out and see for yourself if it makes any difference on your exact setup.


Some users experience wobbles after flashing the 48kHz version. In this case you have multiple solutions: Increase PD gain or decrease I term. in Some cases none of those solutions work and only reverting to th 24kHz version helps. This happens especially on ESC’s with higher deadtimes.

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Chris is a Vienna based software developer. In his spare time he enjoys reviewing tech gear, ripping quads of all sizes and making stuff.

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