Drone propeller won’t stop spinning? 3 Fixes!

You may have an issue with your drone where the propeller just won’t stop spinning unless you disconnect the battery. Maybe this is happened after you have had a little bit of a rough landing or damage the drone in some way. It doesn’t have to be just one of the propellers that won’t stop spinning. It could be that a couple of the propellers also continue to spin after landing. In some extreme cases you may find that the propeller will spin even when the drone is switched off. It will be drawing the power from the battery regardless and stuck on.

If your drone propeller won’t stop spinning you will need to replace the PC board. The PC board contains all of the hardware connection points. This includes any LEDs, propeller motor, cameras, antenna, and battery connectors. It is likely that one of the transistors is deformed in shape. By simply replacing this transistor you can easily stop your drone from spinning. Alternatively, you will need to replace the entire circuit board.

In this article we will be looking at all of the ways that you can stop a drone propeller from spinning and the most important parts of the drone to check and potentially replace.

To understand exactly what is wrong with your drone propeller we need to understand a little bit about the electronics that run a drone.

The electronics of a propeller that won’t stop spinning

The motor of a drone is driven by what is called a pulse width modulated circuit which simply switches the power on and off. The motor uses this pulse width modulated circuit as a speed controller. This pulse width modulator is used to produce analog signals from digital devices such as microcontrollers. Essentially, the pulse with modulation stays on for a particular time and then stays off for the rest of the time. This dictates the speed of the motor.

Connecting the motor to the control board is a transistor. A transistor is used as an electronic switch which can either be in the on or off state. So you can see that it is very likely that if your propeller is continuing to spin the transistor is broken and not switching to the off state.

Replace the faulty transistor

Here are the step by step directions for replacing this the faulty transistor on a drone where the propeller won’t stop spinning.

  • Locate which motor is the one spinning – on the front controller or circuit board where the particular motor plugs in locate a three legged diode nearest the motor. Each motor has the same diode next to it so with a magnifying glass read the markings on top of the transistor this is the number of the part that you will need to replace.
  • Remove the faulty transistor – you can remove a faulty transistor with a bit of flux and a heat gun to remove the old part.
  • Hold the new transistor in place with clips and arms – while holding the transistor in place you need to make sure that it’s not going to move. I recommend using some form of clamp and arm system so that it does not shift from its position while soldering.
  • Use a soldering iron to touch each leg for a second or two each and then place some solder on the joint to connect it to the circuit board.
  • You have to make sure that each leg has been successfully soldered in place by using denatured alcohol to clean the board prior to testing it out.

If you’ve done a good job you will see that the motor no longer spends when you connect the battery. If you are unsure about exactly you are doing check out this really detailed article on building a DIY drone using Arduino – click here. It shows you exactly what the transistor electronic looks like and it may be useful for you to see how a drone is built from scratch.

Here is a YouTube video for how to desolder a component from a circuit board. Please note that the drone circuit board will be much smaller than that demonstrated in the YouTube video but the same things apply:

Look for a bad solder joint

If the transistor does not look like it is damaged and the drone with the propeller that won’t stop spinning is new you could have a bad soldering join on your circuit board. In the first instance you can return the drone for a replacement. But if you are more game than that you can decide to fix a bad soldering join on a circuit board using a solder sucker and a soldering iron. These can be picked up relatively cheaply online.

Here is a fantastic YouTube video on how to fix a bad soda join on a circuit board:

Here are some quick tips that will allow you to solder with a little bit more precision and create a professional quality connection:

  • choose the right soldering iron tip – there are plenty of different types of soldering iron tips and you must use one that allows you to get in contact with the solder without touching any other parts of the circuit board.
  • Clean the tip – it’s always better to use a new soldering iron but in some instances you can use soldering iron tip cleaner to get the grime off the end.
  • You can remove solder by buying a solder wick which is a metal wick that when placed over the solder and heated with a soldering iron it sucks up the old solder.
  • After you have soldered the component it should look like a volcano shape and be shiny. If you do not have a nice peak leading to the connector re-solder the part and try again.
  • Use the right solder – there are many different types of solder. There is lead and tin solder which is about 60% 10 and 40% lead and there is less free solder which is usually tin and silver. Leadfree solder requires more heat to melt so your soldering iron might not be strong enough. Turn up the power if your solder is not melting.

Refer to different methods of soldering and find one that you are most comfortable with. There are plenty of videos on YouTube talking about the best ways to solder. Also, I recommend that you practice on some other scrap parts before you launch into soldering your drone transistor.

Calibrate your electronic speed controller

The electronic speed controller is an electronic circuit that acts as an interface between the pilot commands and the individual drone motors. There are many different types of electronic speed controllers but the types of motors in drones require a three phase controller. The electronic speed controller requires calibration as it is a finely balanced piece of hardware that moves each motor the precise amount so that it can stay airborne and steady. If you are having issues with a motor that won’t turn off consider recalibrating your electronic speed controller to make sure that it is operating in the most efficient way.

Always check the documentation for the brand of ESC that you are using. An “all at once” approach has been noted to work well for most ESCs and can be seen in the video below:

https://www.youtube.com/embed/gYoknRObfOg?feature=oembed There are some ESCs that do not require calibration but check with the documentation if you can change the settings.

What about a DJI drone?

If you are here due to issues with your DJI drone you need to look for your IMU calibration settings. IMU stands for inertial measurement unit and uses data from an accelerometer, gyroscope, thermometer and barometer to determine the drones movements and position.

A lot of the time the DJI GO4 app will prompt you to recalibrate the IMU or compass if it senses an issue. Always follow this advice and calibrate the drone’s sensors. In many cases, it won’t allow you to take off without recalibrating anyway.

Conclusion

There are all of the reasons why your drone propeller won’t stop spinning. In most cases you will need to replace a component of the drones such as the transistor or circuit board in full. This can require a fair bit of electronic soldering experience as these components are very small.

Before launching into soldering and other types of repair reach out to the manufacturer to see if you can get a replacement part or a replacement drone.

Good luck and I hope that you managed to get back in the air as soon as possible!

 

The Author

Dr Andrew Stapleton is a writer and YouTuber with a PhD in science. He has written and/or produced videos for Science Alert, COSMOS magazine, and Australia's Science Channel among others. Andy started droneflyingpro.com to share his love and the research of all things drone! He has been a drone pilot for many years and has flown many types of drone. His favorite is still the DJI Mavic Air for the portability and functionality packed into a small and portable drone!