Drone Motor Protection with Betaflight RPM Alarm🔔

A little known feature in Betaflight you never knew existed. This little-known feature could save your drone's life. Dive in to find out how!

8 months ago   •   3 min read

By Robyn
Table of contents

Introduction

Hey drone enthusiasts! Ever found your FPV drone stuck in a tree, trying desperately to dislodge it, only to end up frying the motor or ESC? Or worse, discovering one of your motors jammed after a crash and a failed attempt at takeoff? We've all been there. But guess what? There's a way to stop this from happening, and it's been hiding in plain sight in your Betaflight settings and Bardwell has just released a video showing you how to set this up! Let's dive into the details.

The Problem at Hand

Most of us, after an unfortunate crash into a tree or a post, tend to use turtle mode or arm the drone to try and shake it loose. But that can backfire. If the prop is up against a branch, trying to spin the blocked motor can create damaging surges of current. This is a surefire way to fry your motor or ESC.

A Solution in Betaflight

Here's the good news. Betaflight can actually warn you if one of your motors is jammed!  If you're someone who crashes a lot (don't we all?), turning on this option could save your drone's life!

The warning we're referring to will pop up in your on-screen display. The warning usually appears in the upper left-hand corner where my OSD warning element is located. When one of the motors is obstructed, a warning pops up showing 'ESC1234'. One of these numbers is followed by an 'R', which signifies an RPM warning, meaning the motor RPM is unexpectedly low. This is your cue that the motor is jammed or blocked. To turn this feature on, go to the CLI and type:

set OSD_ESC_RPM_alarm = 1000.

The warning will show on your OSD, with the motor showing an R, indicating its RPM is lower than what it should be, indicating it could be jammed!

The Caveats and the Catch

However, there's a catch. The flight controller knows the RPM of the motors, but it only triggers this alarm if the RPM of the motors is coming in via ESC Telemetry. So, if you're using bi-directional D shot, which most people do, this isn't going to work. Your ESC will need to have a Telemetry wire that's going to the flight controller. Although most ESCs have a Telemetry wire and can do ESC Telemetry, many people don't use it as most of its functionalities can be covered by bi-directional D-shot.

ESC Telemetry needs to be enalbed for the RPM alarm to work!

So, if you've never set up ESC Telemetry, this option won't work even though the flight controller can identify the RPM of the motors using bi-directional D shot. This might seem like an oversight in the Betaflight code and perhaps they'll update it in the future.

Wrapping it up

Once you have ESC Telemetry set up, you can enable it in the CLI and make sure you have the warning element in your OSD.  

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