IR Comp Adjustment: Most drives have this adjustment. If set too far clockwise the motor will tend to oscillate. Slowly turn the IR Comp trim pot in the counter clockwise direction until the oscillation stops. Speed command signal: An unstable speed command signal to the drive can cause the motor not to run smoothly. Remove the command signal from the drive and use a potentiometer instead. If the motor becomes smooth, the external speed command signal was the source of the problem. Change in load: In most applications a drive can be tuned to run a motor smoothly and compensate for changes in load. But when loads change abruptly, the IR Comp circuit cannot respond fast enough. Make sure there are no mechanical problems in the operation that can cause these abrupt changes in load. A good way to check this is to simply remove the load from the motor and observe how it runs. If operation becomes smooth, you most likely have a mechanical obstruction. Motor brushes: If using a permanent magnet motor, inspect the brushes for excessive wear or irregular wear. It also a good idea to blow compressed air into the brush housing to clean out any carbon build up. If possible, turn the motor shaft as you blow compressed air into the brush compartment. Max speed too high: Having the output voltage to the motor set too high can cause some drives armature output to become unstable. Do not try to run a motor that exceeds the armature voltage that is available to use. For example, you can't run a 180VDC rated motor when you power a drive with 115VAC.