• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Motion Control Tips

Automation • Motion Control • Power Transmission

  • News
    • Industry News
    • Editor Blogs
    • Video
  • Controls
    • HMIs
    • PC-Based Controllers
    • PLCs + PACs
    • Stand-Alone Controllers
    • Software
  • Drives
    • Servo Drives
    • Stepper Drives
  • Encoders
    • Absolute Encoders
    • Incremental Encoders
    • Rotary Encoders
  • Mechanical
    • Bearings
    • Brakes + Clutches
    • Belt + chain
    • Couplings
    • Gears + Gearing
    • Lubrication
    • Shock + Vibration Mitigation
    • Springs + Rings + Seals
  • Linear
    • Actuators
    • Linear Motors
    • Linear Encoders
  • Motors
    • AC Motors
    • DC Motors
    • Brushless Motors
    • Gearmotors
    • Piezo Motors
    • Servo Motors
    • Stepper Motors
  • Systems
    • Conveyors + linear transport systems
    • Gantries + Stages
    • Rotary Tables
    • Grippers + End Effectors
    • Robotics
  • Networks
    • Connections + Sliprings
    • Fieldbuses
    • I/O
    • Sensors + Vision
  • FAQs
    • Motion Casebook
    • Motion Selection Guides
  • Suppliers
You are here: Home / FAQs + basics / What is linear behavior for DC motors?

What is linear behavior for DC motors?

July 6, 2017 By Danielle Collins Leave a Comment

When the term “linear behavior” is used to describe a system, it implies that the system’s output is directly proportional to the input. 

Unlike their wound-field counterparts, permanent magnet DC (PMDC) motors exhibit linear behavior. The use of permanent magnets means PMDC motors don’t need separate field excitation, and therefore, don’t experience the electrical losses that often occur in field windings of other DC motor designs.

In permanent magnet motors, linear behavior is evident in several performance characteristics. First, the motor’s angular velocity (or speed) is directly proportional to the applied voltage, as shown by the equation:

torque-speed

Where:

ω = angular velocity

V = voltage

k = motor constant

T = torque

R = resistance

Second, the motor’s output torque is directly proportional to the current through the armature. The relationship between torque and current is shown by the equation:

Where:

T = torque

I = current through the armature

kT = torque constant of the motor

The linear characteristics of PMDC motors also extend to their torque-speed curves. The linearity of the relationship between speed and torque makes permanent magnet motors ideal for adjustable speed uses and for servo applications.

linear behavior
Image credit: National Instruments Corporation

It’s important to note that DC motors with permanent magnets can be either brushed or brushless types. Brushed permanent magnet DC motors are often referred to as PMDC motors, while brushless permanent magnet DC motors are referred to as BLDC motors. Both motor types – PMDC and BLDC – exhibit the linear behavior characteristics described above.

Despite their similar speed and torque behavior, there are two significant differences between PMDC and BLDC motors. First, PMDC motors are commutated mechanically, via brushes and a commutator, whereas BLDC motors are commutated electronically, typically via Hall effect sensors on the stator. Second, PMDC motors have a stator made of permanent magnets, while BLDC motors have permanent magnet rotors.

For a primer on industry terminology for servo motors, check out this article.


Feature image credit: VEX Robotics

You may also like:


  • Why use brushed servo motors?
  • motor constant
    FAQ: What’s the difference between torque constant, back EMF constant,…
  • Hall effect sensors
    FAQ: What are Hall effect sensors and what is their…
  • nominal voltage
    FAQ: Can DC motors run at lower than nominal voltage?
  • DC shunt motors
    FAQ: What are rotational losses in DC motors?

Filed Under: DC Motors, FAQs + basics, Featured

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

POWER TRANSMISSION REFERENCE GUIDE

DESIGN GUIDE LIBRARY

“motion
Subscribe Today

RSS Featured White Papers

  • Specifying electric rodless actuators: Ten tips for maximizing actuator life and system performance
  • The truth about actuator life: Screw drive survival
  • Top Ten Tips: How to specify electric rod-style actuators for optimal performance, reliability and efficiency

Footer

Motion Control Tips

DESIGN WORLD NETWORK

Design World Online
The Robot Report
Coupling Tips
Linear Motion Tips
Bearing Tips
Fastener Engineering.

MOTION CONTROL TIPS

Subscribe to our newsletter
Advertise with us
Contact us
About us
Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy | RSS