How to Fix Faulty Motor Output on FC

Are you having trouble with motor outputs on a flight controller? One of the motors just doesn’t spin when you arm the quad? In this post I will share some experience how to troubleshoot and fix “dead” motor outputs on an FC.

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Are You Sure Motor Output is Dead?

Sometimes the issue might be a lot simpler than we expect, so let’s go through the standard troubleshooting first.

Don’t forget to remove props first!

Check ESC Power

Are the ESC’s actually getting power? You can check the voltage input of the ESC with a multimeter with the LiPo plugged in.

Listening to Motor Initiating Beeps

When you power up your quad, the motors should make a “start-up tone”.

As soon as you plug in the battery, you should get three short tones like “du-du-du”… Indicating your ESC and motor are getting power.

A couple of seconds later, it should make two longer tones “duuuu…. duuuu….”, confirming the ESC is receiving valid throttle signal from the FC.

If you get the first three “du”, not the last two “du”, then it indicates an issue with your FC not talking to the ESC (correctly), which could be a motor output issue. A couple of quick checks:

• Is the motor signal wire broken?
• Is the motor output pin on the FC somehow shorted to the ground? Take a multimeter, put in continuity mode and check between motor signal and ground pins

How to Check Motor Output

You first want to check and confirm if the motor output is definitely faulty before attempting to fix it.

The method I use to troubleshoot motor output is by measuring the voltage level of all four motor outputs, and see if they are the same.

Your flight controller controls the ESC using PWM signal (Oneshot and Multishot are both PWM signals), or digital signal (such as DShot). Note that multimeters are quite dumb, and it cannot read these signals. However it can act like a low pass filter, and convert these signals into a voltage reading. When you change throttle, the signal changes, so will the voltage reading.

Disconnect ESC signals from the FC.

Connect your FC to Betaflight Configurator.

Measure the voltage of motor output with your multimeter – red probe connects to the motor output while the black probe connects to a ground pin.

Ideally, you should get the same voltage on all four motor outputs.

Now go to the motor’s tab in Betaflight Configurator, and move the slider all the way up to 2000 (100%). Measure the voltages again, you should see the voltage increases with the slider. (it’s quite fascinating the first time you do it :D )

For analog signals like PWM, Oneshot, Multishot, you should be getting around 1.5V when throttle is at 1000 (0%), while that for DShot should be around 0.2V.

When throttle is at 2000 (100%), voltage for analog signals will be higher than 3V, while that of DShot should be around 0.4V.

The exact voltage value doesn’t matter that much, the key is to make sure all the motor outputs are giving the same value at any given throttle. If one of the motor outputs are giving different value, or not giving any value at all, then it’s an indication of a faulty motor output.

Remap Motor Output

You can remap your motor outputs on some flight controllers. If you are not sure which pin to use, it’s best to consult your FC manufacturer, or ask the people where you bought the FC from. Maybe a shot in the dark but worth asking on our forum too, Intofpv.com.

Pins you might be able to use as motor outputs are:

• PPM
• LED Strip
• Soft-Serial

This tutorial walks you through how to remap pins in Betaflight, including motor outputs.