Repair Bulletin Detail

Whatever Happened to Original PacSci Brushless Servomotors?

Pacific Scientific sprang into the servo arena in the late 1980’s with their R series brushless servomotors. Although the “R” in those days indicated the motor employed rare earth magnets, these were not just any rare-earth magnets.

The R Series’ Samarium-Cobalt (SmCo) magnets couldn’t be damaged by temperature or current. Additionally, these magnets’ significant strength allowed the Pacific Scientific R servomotor to have excellent torque-to-inertia ratio. Even when the motor got very hot the torque didn’t diminish, as they would have with “ordinary” magnet material.
The Regal Series Was Born

The cost of Samarium-Cobalt magnets exceeded even that of magnets used today, making R series motors comparatively expensive at the time.  Pacific Scientific soon added a more competitively-priced line, in which the R series received its new identity as the Regal Series.

Some applications continue to exist today that can only be solved by the torque density provided by Samarium-Cobalt magnets. This has helped extend the lifespan and viability of the R/Regal series motors. Motor Systems currently has a stock of refurbished R series brushless servo motors for sale.
Pacific Scientific Introduces the Sentry Series

Pacific Scientific replaced the R motors with the Sentry (S) series, which now featured neodymium-iron-boron (NdFeB) magnets. While similar in strength to Samarium-Cobalt magnets, the newer alternative was much cheaper. The S servomotors were available in number 2 and 3 frame sizes.

Although the Sentry was considered a decent low-cost motor, it wasn’t suitable for applications requiring smooth torque delivery. The S motor had a large component of torque ripple that was caused by a variation of torque as the motor rotated. It was eventually replaced in the late 1990’s by the PMA.

The Sentry Series is Replaced By the PMA

The PMA motors were manufactured in Ireland until all production was moved to the Pacific Scientific plant in Rockford, Illinois. These were the first Pacific Scientific motors to use the M23 style connectors that are now the standard.
The PMA motors had smoother torque delivery than the S series, relegating the Sentry to NEMA mount applications. The PMAs featured all metric mounting and were generally designed for 480 VAC applications, the first Pacific Scientific motor to use that voltage level. It was introduced to the market along with the 480 VAC PacSci SCE900 drives.
PacSci Brushless Servo Motor Repair

Motor Systems Inc. is the factory-approved repair center for all PacSci SCE900 drives.

Editor’s Note: In an earlier blog we told of the rivalry that existed between Pacific Scientific and Kollmorgen before their arranged marriage under the Danaher umbrella. At the heart of this competition were their respective brushless servo motors. This is the first in a series of two blogs that will look back at those two manufacturers’ introductory servo offerings.

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