I assembled a frame to balance my motors. The frame is composed of a thin piece of wood clamped to my workbench, with a mirror on it. I attach a motor to the wood, spin it up, then direct a laser pointer to deflect off the mirror onto the far side of my shed. That way, any deflections of the mirror due to vibration will manifest themselves as a line appearing on the laser strip at the end of the room.
|Motor balancing jig|
|The strip of laser light when a motor is unbalanced|
As it turned out, happily two of my motors were quite balanced and needed no adjustments. However, two were off by so much I had to tape a small washer to each one in an appropriate location to reduce the length of the laser strip when it’s running. Note that an enormous amount of centrifugal force is generated when the motor is running, so make sure that your tape is firmly attached before spinning up. Several bits of tape got spun straight off the motor, which was pretty surprising.