text: <s>[INST] 2HP PF755 Motor Speed Varying with Encoder Feedback Summary: Closed Loop Speed Control is PoorHello. I have been getting beat-up by this drive path over the past few weeks. It is a 2HP/480V/1750rpm application with a PF755/2HP connected to a known well-performing Marathon Blue Max 1024 Quad Encoder-Feedback motor taken from another line during troubleshooting. 150W brake resistor is connected. Control is entirely over Ethernet. This motor goes through a ~20:1 right angle gearbox with an output driveshaft down to a small meltpump. VFD cable is used to the motor with no terminations in-between. Control mode is Induction FV. Speed regulation is poor at +/-3% and load swings of +/-15% degrading to load swings of +/- 100%. Other paths with the same setup are rock-solid with very tight speed control - no deviation from set point is seen on the scada hmi. I have attached a video showing this. Motor/Encoder has been replaced, gearbox has been replaced. The speed control fluctuations persist even when disconnected from the load. The original new drive was just replaced with another new drive today. It has been Calculate, Static & Rotate tuned without successfully eliminating the speed hunting. Once again, the other paths on the machine are absolutely stable. Our process requires tight speed control. Any ideas where to look next? Thanks in advance, -dan [/INST] You did not say that you'd done an inertia tune, only the calculate/static/rotate tune that characterizes the motor winding. You need to do an inertia tune, and even after that, I suggest increasing the speed regulator bandwidth (P636). Assuming you use DriveExecutive or CCW, when you do the inertia autotune, after it completes it shows speed reg BW at the bottom. It never, ever changes this; the default I've always seen is 10 rad/s. After autotuning, before moving to the next page, change it. If you have a 20:1 gearbox. Try a value of 30. If that does not work, then go to P636 directly and increase it to 50. Also, be aware that, unless the drive was brand new / broke the box seal to install it, a drive previously used does not completely wipe itself when running the autotune wizard. We've found out the hard way that a drive autotuned for a small motor, then switched to a larger motor keeps some parameters that were appropriate for the small. We've found that you have to do a factory-reset ON THE HIM in order to clear out all parameters. Doing it from DriveExecutive / CCW is not enough. If your new drive was actually a drive new to the application but had been tuned to a different motor, that might explain some of your results. \\n </s>