55NM81-120-2 Pacific Scientific
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The Pacific Scientific 55NM81-120-2 is part of the Low Inertia PMDC Servomotors series and features a rated power of 280 Watts with a rated speed of 1460 rpm. This servomotor is designed with a rated torque of 1.82 Nm, a maximum speed of 2500 rpm, and a rated current of 12.2 Amps. It has a back EMF constant of 17.7 V per 1000 rpm and a rotor inertia of 71 × 10^-6 kg·m².
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Product Description:
The 55NM81-120-2 is a permanent-magnet DC servomotor produced by Pacific Scientific and supplied in the Low Inertia PMDC Servomotors series. Designed for industrial automation axes that require fast acceleration and repeatable velocity loops, the motor converts low-voltage DC drive power into controlled rotary motion while keeping mechanical inertia low. The permanent-magnet field reduces armature losses, making the unit suitable for battery-powered mobile platforms and compact assembly stations. Its low-inertia rotor also helps the motor respond quickly during short indexing moves, frequent starts, and rapid reversals.
Under continuous duty, the motor is rated for a supply of 36 V and draws a nominal current of 12.2 A. At that operating point, it delivers 1.82 Nm of shaft torque and reaches a servo speed of 1460 rpm, providing a mechanical output of 280 W. The 0.8 K/W thermal resistance shows how readily internally generated heat moves to the housing, which is useful when the motor is mounted to a conductive surface or used with added airflow. A back-EMF constant of 17.7 V per 1000 rpm indicates the voltage generated during rotation, and a rotor inductance of 1.2 mH influences current ripple and current-loop smoothness. The electrical time constant of 1.85 ms shows how quickly armature current follows command changes, which supports stable drive response during changing loads.
For transient moves, the drive can command up to 10.1 Nm of pulse torque while the armature carries 60 A for short intervals. Peak velocity is limited to 2500 rpm, and the no-load speed of 1775 rpm shows that friction and iron losses remain low at typical working voltages. Dynamic response is supported by a mechanical time constant of 1.6 ms and by the low rotor inertia of 71 × 10⁻⁶ kg·m², allowing rapid direction changes without making the axis feel sluggish. With a torque constant of 0.169 Nm/A, the controller can estimate output torque from measured current, which helps with current-based control and smooth torque delivery during acceleration.
Frequently Asked Questions about 55NM81-120-2:
Q: What is the rated torque of the 55NM81-120-2 servomotor?
A: The 55NM81-120-2 PMDC servomotor has a rated torque output of 1.82 Nm.
Q: What is the maximum pulse current the 55NM81-120-2 can handle?
A: This model supports a peak pulse current of 60 A, enabling high short-term acceleration.
Q: What is the rated voltage of the Pacific Scientific 55NM81-120-2 servomotor?
A: The rated voltage for the 55NM81-120-2 servomotor is 36 V.
Q: What is the maximum speed capability of the 55NM81-120-2 servomotor?
A: This servomotor can achieve a maximum speed of up to 2500 rpm.
Q: What is the back EMF constant of the 55NM81-120-2 servomotor?
A: The back EMF constant for this model is specified at 17.7 V per 1000 rpm.
