How to Fix ESC Desync in FPV Drones: Tips & Fixes

ESC desync is one of the most puzzling and frustrating issue in FPV. 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.

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What’s an ESC Desync?

In simple terms, a desync occurs when the ESC loses synchronization with the motor. When the ESC and motor go out of sync, the ESC’s commutation timing—essentially, the precise timing it uses to keep the motor spinning—gets disrupted. As a result, the motor stalls and causing your drone to crash. The drone experiencing ESC desync also makes stuttering noise or a specific motor acting erratically before the fall.

However, 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 (all motors stop 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 because all the motors are still spinning except one.

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

Desync occurs when the ESC’s timing of the commutation sequence fails to keep up with the motor’s movement. This misalignment results in a loss of synchronization, and the motor essentially stops. Here are some common causes:

Excessively High RPM

Motors with ultra-high KV ratings or those spinning at RPM that is too high for the ESC to handle, are more prone to desync issues. As the motor spins faster, the ESC has to process the commutation timing more rapidly to keep up. In extreme cases, the ESC can struggle to maintain synchronization, resulting in desync.

When the motor is spinning too fast, 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.

Sudden Speed Changes

If the motor changes speed too quickly, the ESC may not be able to adjust its commutation timing fast enough, causing it to lose sync with the motor. This is especially common in situations requiring rapid throttle changes, like aggressive maneuvers or hard braking during freestyle flying.

Damaged ESC or Motor

Physical damage to either the ESC or motor can lead to desync. For example, damaged motor windings or a faulty ESC can disrupt the precise control required for commutation, leading to synchronization issues. In my experience, older motors or ESCs that have sustained wear and tear are more prone to desyncs.

Electrical Noise

Excessive electrical noise can interfere with the signals between the ESC and the motor, leading to desync. This can be caused by wiring issues, poor connections, or other components creating electrical interference.

Not Everything Is Desync

One of the most common misconceptions is that any incident causing the quad to drop is a desync. However, not all issues that look like desyncs are actual desyncs. Here are some examples of issues that can mimic desyncs:

• Burned Motors: If a motor draws too much current and burns out, the quad might spin out of control and crash. While it might look exactly like a ESC desync in video, it’s not caused by ESC desync.
• Overheating or Faulty ESCs: If an ESC malfunctions or overheats (e.g. temperature protection), it may cut out, causing the motor to stop. Again, this isn’t a classic desync but rather an ESC issue.
• Battery Voltage Drops: A sharp drop in battery voltage can cause the ESC to lose power momentarily, leading to motor cutoff. This can look like a desync but is actually a power issue.

Solutions to ESC Desync

Select the Right ESC and Motor Combo

To prevent ESC desync in the first place, choose an ESC and motor combination that works well together. Motors with very high KV values should be paired with modern ESCs capable of handling fast commutation speeds.

Use Additional Filtering Capacitor

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/

BLHeli and Betaflight Settings

To fix ESC Desync, or reduce the likelihood of its occurrence, you can try different settings in BLHeli and Betaflight. Not all the suggestions may be necessary, but one or some of them could be the answer to your problem.

BLHeli Settings:

• 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.

Avoid Sudden Throttle Changes

Flying aggressively with rapid throttle changes can increase the chances of desync, especially if your ESC isn’t keeping up with the speed changes. If you’re experiencing desyncs during aggressive flying, try easing off the throttle changes or adjusting your flight style to reduce stress on the ESC.

Can ESCs Recover from Desync?

In some cases, ESCs are capable of recovering from a desync mid-flight. When a desync occurs, the ESC may enter what’s known as “blind commutation”. Normally, the ESC senses the motor’s position and adjusts its timing accordingly. In blind commutation, however, the ESC attempts to estimate the motor’s position without precise feedback, hoping to regain synchronization.

If the ESC succeeds, you might experience a momentary stutter, but the drone will continue flying. However, if the ESC fails to resync, you’ll experience a “death roll” where the motor completely stops, causing the drone to tumble and crash.

Conclusion

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/

Happy flying!

Edit History

• July 2021 – Article created.
• February 2024 – Updated.