 Due to the eccentric nature of the drive, if the cycloidal disk is not balanced by a second disk or a counterweight, it will generate vibration which will propagate through the driven shafts and the body.This will cause increased wear on the exterior teeth of the cycloidal disk, as well as component bearings.With two discs the static imbalance is corrected but a small dynamic imbalance remains, this is generally considered acceptable for most applications but to reduce vibration high speed drives use three (or more) discs to allow the imbalance to be corrected, the outer discs move in unison and in opposition to the middle one which is twice as massive.