Product Description:

The 4VM81-220-5 is a low-inertia permanent-magnet DC servomotor built by Pacific Scientific and supplied within the Low Inertia PMDC Servomotors series. Designed for precision industrial automation, this motor converts armature current into tightly controlled torque for positioning tables, pick-and-place heads, or rotary actuators that must accelerate quickly without overshooting. Its permanent-magnet field eliminates external excitation hardware, while the low-inertia armature allows fast reversal and accurate following of drive commands, making the unit suitable for closed-loop velocity or torque loops in servo drive systems.

Commutation is accomplished through carbon brushes, a choice that keeps contact resistance low and mitigates arcing at higher armature speeds. These brushes are also field-replaceable, so routine maintenance can be completed without disassembling the laminated core or magnet assembly. No encoder is attached, so velocity feedback is provided by the standard tachometer unless an external encoder is added. Thermal management relies on an air inlet/outlet with baffles that steers forced air across the internal heat path. With that airflow, the motor can provide up to a 200% torque gain for short duty periods. When subjected to rapid accelerations, the motor can momentarily deliver 5× rated peak torque, allowing it to start heavy inertial loads without oversizing the drive amplifier.

Torque density comes from an Alnico V permanent-magnet ring that resists demagnetization during high current bursts and from a basket-wound hollow rotor that minimizes rotating mass while sustaining mechanical rigidity. Speed feedback is provided by a standard analog tachometer; the sensing drum has a 2.765 in tachometer diameter and a length of 2.062 in, producing a voltage proportional to shaft speed with ±0.5% linearity across its specified range. With provisions for either front or rear encoder mounting, digital feedback can be added when tighter position control is required.