Motor Tuning - The Practical Approach
There are five tuning values that can be used to achieve smooth, accurate motion. To adjust these values, select the motor you wish to tune in the Cue Grid and select the Tuning section in the Stagehand Properties Panel.
P-Gain is the ratio of power to position error. The higher this value, the more power will be applied to correct for position errors. This is often the only tuning value you will need to adjust. P-Gain needs to be at least “1” for the motor to move at all. If the value is too high, the motor will begin lurching. Sometimes this lurching can be extreme so make sure to have your hand on the Emergency Stop when you first adjust this value.
D-Gain is applied against changes in position error. It can have a dampening effect on a motor, absorbing the shocks from a high P-Gain. Typically apply at intervals of 100.
This describes how often the Derivative Gain should be applied. If you are using Derivative Gain, Derivative Sampling must be set to at least “1.” Rarely (but not never) is there any benefit to using a Derivative Sampling value higher than “2.”
I-Gain or Integral Term, tries to compute corrective action by evaluating the position error and motor response over time. From a practical standpoint, I-Gain will often correct the motor’s position at the end of travel. This can be helpful if you need to reduce Proportional Gain to smooth out a motion, but then lose accuracy. In such a scenario, adding in 1 or 2 points of I-Gain will often retain accuracy without sacrificing smooth travel.
Integral Limit prevents a condition known as Integral Windup, which can lead to really erratic motor behavior. If you use an Integral Gain, set Integral Limit to 1000.
Over the past several years, we’ve come up with a practical approach to motor tuning that yields good results in a reasonable amount of time. That approach is shown in the form of a flow chart. The steps are clear and simple, but it can still be a frustrating experience the first time you attempt to tune a motor. It’s extremely important to find at least an hour of quiet time on the stage without anyone else working around the moving scenery. Get a cup of coffee, relax, focus and take a stab at it. If that doesn’t work, give us a call. - we have had plenty of experience helping people tune motors over the phone. The good news is that it gets a lot easier once you see it work the first time.