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Why Do Quadcopter Motors Spin Up by Themselves? (Solved)

So, you have just bought your first quadcopter or built one for yourself. Congratulations! You may have observed, however, if you’re testing out your quadcopter motors with the propellers off, that the motors spin up by themselves, and you have no idea for the reason behind this is. You double and triple-check everything but still can’t find an apparent reason why this is happening. Well, if your quadcopter is exhibiting such behavior, we have just the answer you are looking for.

If you’re throttling up your drone with the propellers off, it’s normal for the motors to spin up on their own. This doesn’t mean they will do the same thing with the propellers attached. The motors spin up because of the buildup of the “I” value of the PID component. 

In this article, we will discuss why quadcopter motors spin up by themselves. We will also talk about how to fix quadcopters that spin around on take-off. If either of these issues are something that you’ve run into, we’ll offer some helpful tips to resolve it.

Why do quadcopter motors spin up with props off?

The answer to this question lies in the technical understanding of how multirotor drones maintain stability in flight. A control system called the PID controller essentially uses a feedback loop to convey information from the sensors on the flight controller to make a change or adjustment through the motors on the drone. The sensors “read” how well those commands carry out the intended change, and make additional adjustments as necessary to try to achieve the desired command. 

To understand why motors spin up when throttled up with the propellers off, we need to understand the “I” constant, a function of the PID controller. The “I” constant represents the differential between the intended command or value, and what the PID senses the value to be in real life. 

When the propellers are not attached, the throttle command instructs the motors to spin until lift is achieved, but the sensors are instructing the controller that this is not being achieved. The feedback loop results in a buildup of the “I” constant, causing the motors to continue to spin faster and faster. This phenomenon is commonly referred to as “I” term windup.

When propellers are installed, this feedback loop of command with no result is broken, hence you should not see motor spin up of this kind unless you are throttling up your quad without propellers attached. 

Why does my drone keep spinning?

It can be quite frustrating to observe your drone spinning uncontrollably for no obvious reason. One of the simplest explanations for a drone spinning around on take-off is that your transmitter may just require a bit of calibration and trim adjustment to stop your drone from spinning. However, there may be some other reasons why your drone keeps spinning, and in this section, we’ll have a look at them.

1. Incorrectly installed or damaged propellers 

Each propeller used for each motor should match the direction the respective motor is spinning. On a quadcopter, there are two clockwise propellers and two counterclockwise propellers. Having the wrong propeller on the wrong motor can cause your drone to not only spin but also flip over or refuse to take off. 

This should be easy to fix. Check your user manual to make sure you’ve installed the correct propellers on the correct corners. 

Another reason your drone may be spinning is if there is damage to your propellers. Even slight damage to your drone’s propellers, such as a chip or crack, may be responsible for your woes. If you find damage on any propeller, you should replace it and see if this fixes the spinning problem.

2. Miscalibrated ESC

The ESC, also known as Electronic Speed Controller, connects your drone controller to the motor. It detects the signal from your controller and takes power from the battery to make the motors spin. This may seem simple enough, but with multiple motors to spin, this means that different ESC’s need to be working in sync. If this is not the case and one is slightly out of sync with the rest, your drone starts spinning.

This is why ESC calibration is important. The process of calibrating the ESC varies among different drones, so you should consult your drone’s manual on how to do so.

3. Poorly calibrated compass

Most drones have an built-in compass which it uses to determine direction. The compass determines which direction your drone is facing while in flight. And just like the compass on your smartphone, the drone’s compass has to be properly calibrated for the drone to fly correctly.

One of the reasons your drone may be spinning is if the compass hasn’t been properly calibrated. To fix this issue, you should read the manual that came with your drone to know how to calibrate it properly. Different drones have different methods of compass calibration.

4. Motors spinning in the wrong direction

All motors should be spinning in the right direction (two clockwise and two counterclockwise, on opposite corners). There are various drone motor setups for different drones, so you should consult the manual to make sure the motors are spinning in the right direction; otherwise, your drone will keep spinning in circles.

If this is the culprit, you have two options. The first is that you can swap the wires from your ESC to that particular motor that’s the problem. The second is that you can use software to configure your ESC.

5. Motors spinning at different rates

If your drone motors are configured correctly and are spinning in the right direction, but your drone is still spinning, the reason may be that one of your drone’s motors isn’t spinning at the same speed or with the same power as the rest. A lack of balanced thrust in one or more drone motors can cause the drone to spin out of control.

You can solve this problem easily by calibrating your ESC. If you had already done this, then the reason your drone may be spinning is if one or more motors are not in good working order or have debris or hairs tangled in them. Try cleaning the motors to see if this resolves the issue.

6. Miscalibrated IMU

IMU stands for Internal Measurement Unit, and if this is not properly calibrated, you may experience your drone spinning. The IMU is essential because it detects acceleration changes and fixes your drone’s spinning problems. The IMU has gyroscopes that detect and fix changes in roll, pitch, and yaw. When talking about spinning, what we’re really referring to is motion on the yaw axis of your drone.

So, fixing the spinning problem on your drone could be as simple as calibrating your quadcopter’s IMU. Once this is done, your drone will fly correctly. You should go through your drone’s manual for instructions on how to properly calibrate your IMU. Once this is done, you’ll know whether the IMU was the cause of your drone spinning or not.

Try each of the pointers in this article to diagnose the cause of the spinning problem with your drone and fix it appropriately.