If one blade is spinning faster than another, then the helicopter won't lift off. The first thing to check is the gears driving the blade shafts. It could be that one of the gears is not set properly, or there is something caught near the shaft. Pet hair can often wrap around the shaft and cause drag. If the gears appear to be in the correct positions, and meshing with the pinions (small gears) on the motors, and there is nothing wrapped around the shaft, such as hair, I would slowly increase power and see if both motors start spinning at the same time. If they don't, there could be a problem with the motor, or the controller board. If this is the case, it may be repairable, but might be just as cheap to replace the whole helicopter. Hope this helps!
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If one blade is spinning faster than another, then the helicopter won't lift off. The first thing to check is the gears driving the blade shafts. It could be that one of the gears is not set properly, or there is something caught near the shaft. Pet hair can often wrap around the shaft and cause drag. If the gears appear to be in the correct positions, and meshing with the pinions (small gears) on the motors, and there is nothing wrapped around the shaft, such as hair, I would slowly increase power and see if both motors start spinning at the same time. If they don't, there could be a problem with the motor, or the controller board. If this is the case, it may be repairable, but might be just as cheap to replace the whole helicopter.
Hope this helps!