The most simple method I have found to balance a brushless motor is using an application on my mobile phone. By simply running up the engine while the application records vibrate, I slowly adjust the vibration with a small piece of tape repeating this process until the vibration measurement is at its minimum.
I’m using a Samsung Galaxy 7 and a free application called Max Vibrometer. I like this application because I can pause the reading to note it down. Any vibration app will work but it’s much easier if you have a fixed number on screen.
Ensure you work safely
Remove any props on your multicopter and place your multicopter on a level surface with something to stop it from moving around. My multicopter has material on the landing gear that works well, although taping the multicopter to the table works too.
Tape vibration absorbing material on the bottom of your phone
This helps the phone to stay in place when testing and reduces vibration to a manageable working level.
Tape over foam which is discarded protective packaging.
Tape your phone to an arm of your multicopter
Obtain an initial vibration reading
Ensure you only have one motor running at a time. Run your motor up to full throttle and press the hold button in the vibration app (if you’re using the same app as me). Now throttle down and record the reading somewhere.I only use the Z value as my reference.
Obtain a second reading
By placing one small piece of tape on the side of the motor, you may increase or decrease the vibration. Simply repeat step 4.
Start tweaking the vibration level
Now that you have another reference, move the tape slightly to the left. If the Z value decreases, you’re on track. Simply keep moving the tape to get the lowest possible reading. Once you have gone quite low in the Z value and it starts to go up again, go back one position as you have found the lighter side of the brushless motor housing.
Continue tweaking the vibration level
Now that you have found the lightest side of the brushless motor, it’s time to start adding small pieces of tape at a time to reduce the vibration down as far as you can. Continue running the motor up and recording the Z value.
Finish the job
Now that you know how much tape is required to fix the vibration, make note of where the current position of the tape is either by marking it with a pen or by having your tape ready to swap out. Place new fresh tape in that position so it will remain in place permanently. Perform one final run up to see if you have the same Z value (or lower if you’re lucky).
Written by Thomas