Introducing Oneshot ESC Protocol – Better FPV Drone Performance Than PWM

In this post, we’re diving into Oneshot125, a cutting-edge ESC protocol designed to enhance the responsiveness of your FPV drone beyond the traditional PWM signal. We’ll explore what Oneshot is, and introduce the BLHeli feature, Active Braking (damping light), which dramatically improves throttle response.

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Understanding ESC Protocols

An ESC protocol is crucial for communication between the flight controller (FC) and the electronic speed controller (ESC), which governs the motor’s rotation speed. Traditionally, this communication has relied on PWM signals, ranging from 1000ms to 2000ms (0% to 100% throttle). However, PWM is pretty slow for FPV drone applications, and can be prone to jitter, leading to the development of Oneshot125.

For a comprehensive overview of ESC protocols, check out this article: https://oscarliang.com/esc-firmware-protocols/

What is Oneshot?

Oneshot125, specifically tailored for FPV drone, is a faster alternative to PWM. Created by firmware developers who synchronized the ESC signal with the PID loop, it reduces susceptibility to jitter. Oneshot uses a shorter signal width, allowing the FC to communicate with the ESC/motor more rapidly, theoretically enhancing your multirotor’s performance.

To use Oneshot125, ensure your flight controller supports the feature and that your ESCs are updated with the latest BLHeli firmware, which recognizes the protocol automatically. This post will cover why Oneshot125 outperforms standard PWM and guide you through enabling it on your ESCs. We’ll also delve into the advantages of Active Braking (Damping light).

Note: With OneShot, the motor_pwm_rate is disabled in Cleanflight, so its setting becomes irrelevant.

How Oneshot Improves Drone Performance

Traditionally, a flight controller operates with a main control loop that calculates motor outputs based on sensor data. This calculated value is then picked up by the main control loop and sent to the ESC. However, the duration it takes to complete a flight controller (FC) main control loop can vary.

With the standard PWM motor output signal, whatever value is available is sent—whether it’s new or old. If we’re fortunate, the ESC may pick up a new value recently produced by the FC. But at times, a new value isn’t picked up immediately, possibly because the ESC is still processing the old one. This can mean the value being written to the motor is old.

Though this scenario doesn’t typically cause significant issues, as the time differences are minimal (we are talking about just a few milliseconds here), some developers have proposed a solution.

Oneshot – The New Approach

Oneshot125 addresses the above issue by synchronizing the FC’s main control loop with the motor output signal, implementing two key changes:

1. Increased Timer Speed: Oneshot125 boosts the motor output timer speed to eight times faster than standard PWM. While traditional PWM signals range from 1ms to 2ms, Oneshot reduces this to just 125us-250us. This accelerated pace means data is transmitted to the ESC more quickly, mitigating the issue of delayed value updates.
2. Single Signal Per Loop: Oneshot only sends one pulse of the signal per flight controller loop, immediately after the FC has a new value ready for the ESC. This is likely the origin of the name “Oneshot.” The ESC begins writing this new value to the motor even before the FC starts its next control loop, resulting in quicker responses from both the FC and the ESC.

Pilots who have tested Oneshot125 report minimal improvements in PID gains but significant enhancements in throttle response, including faster changes in motor speed.

For a straightforward explanation of how quadcopter PID works, check out this post on Quadcopter PID: https://oscarliang.com/quadcopter-pid-explained-tuning/

How to Enable Oneshot on Your ESC

For those looking to enhance their FPV drone’s responsiveness and speed, enabling Oneshot on your ESC is a vital step. Here’s how to ensure that your ESCs are compatible with Oneshot125 and properly updated with the new BLHeli firmware. Your flight controller (FC) must also be updated to the latest firmware that supports Oneshot.

Supported ESC and Firmware

ESCs that are flashed with BLHeli rev13.0 or a newer version support Oneshot and will automatically detect the protocol without additional configuration. Recent updates to SimonK firmware now also include support for Oneshot.

Supported Flight Controller Boards / Firmware

All flight controllers that are compatible with the latest versions of Cleanflight, Betaflight, Raceflight, and KISS now support Oneshot.

Calibrating Oneshot ESCs

The calibration process for Oneshot ESCs mirrors that of standard ESCs:

1. Ensure your ESCs are disconnected from the LiPo battery.
2. Remove the propellers for safety.
3. Connect the board to your PC and open the Cleanflight configurator, navigating to the motor test tab.
4. Activate “TEST MOTOR” and set all motor speeds to maximum using the master slider.
5. Connect the LiPo battery to your ESCs; they will emit a beep to indicate calibration mode.
6. Quickly drag the slider down so the motor speed is now zero. The ESCs will beep again to confirm successful calibration.
7. Disconnect and then reconnect the battery to your quadcopter. Check that moving the motor slider causes your motors to spin up normally and simultaneously.

Don’t Forget Active Braking!

Active Braking, also known as Damping Light, is a feature in the latest BLHeli ESC firmware that many pilots enable alongside the Oneshot protocol to achieve more responsive performance.

With Active Braking enabled, your ESC will actively reduce motor speed faster as you lower your throttle, instead of just letting the props slow down passively through air resistance. This results in more responsive throttle control and a more agile quadcopter. Without it, the quad may feel more “floaty.”

Caution: Active Braking can cause voltage spikes during braking, which might disrupt your video feed or potentially damage the electronics in your mini quad. Installing low ESR capacitors at the power or ESC can mitigate this issue: https://oscarliang.com/capacitors-mini-quad/

More Info and Resources

For the foundational post on Oneshot125 and documentation, refer to Cleanflight’s official guides: https://github.com/cleanflight/cleanflight/blob/master/docs/Oneshot.md

See Hydra demonstrating the difference between normal PWM and Oneshot on an Oscilloscope:

Exploring More Advanced ESC Protocols

As technology evolves, so do the protocols. Apart from Oneshot125, the market now features more advanced ESC protocols like Oneshot42, Multishot, and D-Shot, each offering distinct advantages for specific flying styles and needs.

• Oneshot42
• Multishot
• D-Shot

Edit History

• Mar 2015 – article created.
• Apr 2024 – fixed grammar.