When one of the motors in your FPV drone stops spinning unexpectedly, causing it to tumble out of the air, it might be due to ESC Desync. This article discusses the reasons, and tips to fix ESC desyncs using BLHeli and Betaflight settings.
Table of Contents
What’s an ESC Desync?
Not every instance of a “drone falling out of the sky” is due to ESC desync. For instance, if your quad drops to the ground without any spinning, it could simply be a failsafe or loss of power. Typically, during an ESC desync, the drone will spin or roll rapidly out of control.
The best way to identify an ESC desync is by examining Blackbox logs. An ESC desync occurs when one of the motors stalls (stops spinning and thus stops producing thrust), prompting the drone to command that motor to spin harder, causing the motor signal to reach its maximum of 100%.
New to Blackbox logs? Don’t worry I have a complete tutorial here to get you started: https://oscarliang.com/blackbox/
Without Blackbox, examining DVR footage frame by frame can sometimes offer clues about the direction of the roll and which motor experienced the ESC desync—the one that goes down first.
Causes of ESC Desync
Common causes of ESC desync include:
- Excessively high RPM (motors running faster than the ESC can handle).
- Too much electrical noise.
When motor RPM is too high, the ESC can miss the motor’s “zero crossing” (commutation), while electrical noise can exacerbate the situation. If the ESC cannot accurately detect the “zero crossing,” it will not know when to fire the next pulse (to create the necessary magnetic field to push the motor), leading to the motor eventually stalling.
Solutions to ESC Desync
To fix ESC Desync, or reduce the likelihood of its occurrence, you can try changing some settings in BLHeli and Betaflight. Not all the suggestions may be necessary at the same time, but one or some of them could fix your issue.
However, firstly, it’s crucial to have a low ESR capacitor soldered to your ESC’s power input if you haven’t already done so; it can help reduce some of the electrical noise – often times it’s the root of the problem. I have a guide on the type of capacitor you should choose, and where to solder it to: https://oscarliang.com/capacitors-mini-quad/
- Rampup Power (or Startup Power): Use a lower value, such as 0.125 in BLHeli_S or 12% in BLHeli_32. If the props hesitate to spin when you arm the quad, you might need to slightly increase the rampup power until you find the sweet spot where the motors start spinning smoothly upon arming the quad without causing ESC desync.
- Demag Compensation: Set to high, as it aids the quad in recovering from desyncs instead of merely dropping to the ground, albeit at the cost of some performance.
Only adjust these settings if your quad experiences desyncs. For more detailed information on what these settings do, refer to this guide: https://oscarliang.com/best-blheli-32-settings/.
If BLHeli settings are insufficient, you can also try the following settings in Betaflight:
- Use DShot ESC Protocol if you are not already using it.
- Motor Idle Throttle Value: The default is 5.5, which is quite conservative for smaller quads. Try a slightly higher value like 6.5 or 7.
Hopefully following these tips helped resolve your ESC Desync issues, and now you should consider tuning your quad by following these 10 simple steps :) https://oscarliang.com/fpv-drone-tuning/
- July 2021 – Article created.
- February 2024 – Updated.