Questions answered to demystify servo sizing

Extra questions about servomotor sizing are answered here, from a May 17 webcast, archived for a year. More help includes related services and software, more servomotor sizing errors and information needed for servomotor sizing.

By Sixto Moralez June 16, 2022
Courtesy: Yaskawa

Audience members participating live in the May 17 webcast on “Demystifying Servo Sizing” have their additional questions for the speakers answered below to help learn how to properly size or retrofit servomotors in a machine design or other motion control project.

Speaker for the webcast is Sixto Moralez, senior regional motion engineer, Yaskawa America Inc. The webcast, archived for a year, was moderated by Mark T. Hoske, content manager, Control Engineering.

Question: Do you offer services to assist me in sizing my application?

Moralez: Yes, please contact your local distributor/integrator or Yaskawa Sales Representative for further assistance.

Question: You discussed common mistakes made when sizing. Of these, which happen most often and why?

Moralez: The most often is the crossover manufacturer trap since the machine is already working and the easiest thing to do is copy/paste specifications as close as possible. However, how do you know the axis isn’t oversized already and then increase the capability 20% more? Furthermore, all manufacturers aren’t the same and the specs won’t be either.

Question: Aside from the errors mentioned, are there things people overlook or may ignore?

Moralez: Most people ignore the inertia ratio mismatch since the data shows enough torque and speed.

Question: Before sitting down with motor-sizing software, what do I need to bring to the computer?

Moralez: Bringing a general understanding of the application would assist in the sizing process. However, the following is a list of data that should be gathered:

  • Payload of object moved
  • Mechanical data (ID, OD, lengths, densities)
  • What gearing is in the system?
  • What is the orientation?
  • What speeds are to be achieved?
  • How far does the axis need to travel?
  • What is the required precision?
  • What environment will the machine reside?
  • What is the duty cycle of the machine?

Question: I’ve seen some shaky motion control demonstrations at various shows over the years. Are these sizing issues or could they be something else?

Moralez: Depending on the inertia mismatch, this shaky motion could be system tuning. Either the gains are too hot or the load has a low frequency that would need to be suppressed. Yaskawa’s Vibration Suppression can help.

Question: Any other advice you’d like to offer about servomotor applications?

Moralez: Many people disregard the use of software to guide in the selection process. Take advantage of Yaskawa’s SigmaSelect software to validate the data when sizing servomotors.

Sixto Moralez is senior regional motion engineer and Latin America sales manager at Yaskawa America Inc. Edited by Mark T. Hoske, content manager, Control Engineering, CFE Media and Technology,

KEYWORDS: More answers about servomotor sizing

Review common servomotor sizing errors.

Examine what you need to gather before using servomotor sizing software.

Get additional advice about servomotor sizing.


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Author Bio: Sixto Moralez is a senior regional motion engineer for Yaskawa America, Inc. His diversified, worldwide experience comes from time invested in the field. He holds a bachelor’s degree in electrical engineering from DeVry University in Irving, Tex.