Limited Angle Torque Motors

Overview

Limited angle torque motors (torquers) are brushless rotary actuators designed for precise angular positioning with exceptional acceleration capabilities. Operating on electromagnetic principles, these motors produce torque proportional to input current, enabling intricate control of angular position, velocity, and acceleration when paired with servo electronics and feedback devices.

The low-profile design and minimal rotor inertia make torquers ideal for applications requiring rapid angular movements in confined spaces where conventional rotary motors cannot fit. Available in two distinct series—TMR (iron core) and TWR (moving coil)—these motors accommodate angular excursions from 60° to 360° with continuous torques up to 1000 oz-in.

How Limited Angle Torque Motors Work

Limited angle torque motors operate on the Lorentz Force principle: when a current-carrying conductor is placed in a magnetic field, a force (torque) is exerted upon it. This torque is proportional to both the magnitude and direction of the current and the magnetic flux density.

Since the permanent magnet flux field is fixed, rotation direction depends on input current polarity, while torque output is directly proportional to current magnitude. When integrated with a bearing system, shaft, and rotary encoder or feedback device, the torquer achieves precise angular control.

Power & Control: A DC linear servo amplifier supplies current to the torquer based on commands from a motion controller. The feedback device continuously monitors position (typically 500 times per second), allowing the controller to adjust current in real-time for accurate positioning, velocity control, and acceleration profiles.

Low Inertia Advantage: The minimal moving mass of the rotor assembly enables exceptionally high angular accelerations, making these motors suitable for dynamic applications requiring rapid direction changes.

Key Components

TMR Series (Iron Core Design)

Stator: Toroidally wound copper magnet wire on a soft magnetic steel toroid with electrical insulation. Only 2 leads exit the stator assembly.

Rotor: Rare earth permanent magnet assembly with 2, 4, or 6 poles. Maximum angular excursion varies by pole count:

• 2-pole: Up to 180°
• 4-pole: Up to 90°
• 6-pole: Up to 60°

Torque decreases to zero at travel extremes. For constant torque throughout rotation, actual excursion is less than maximum.

Magnetic Interaction: Radial attractive forces exist between stator and rotor. When properly centered, these forces balance and cancel each other out.

TWR Series (Moving Coil Design)

Rotor: Single coil of bondable copper magnet wire wound and preformed into shape, held together by bonding agents. Can be encapsulated with aluminum or plastic brackets for mounting. Maximum angular excursion typically under 90°.

Stator: Multipole permanent magnets bonded to steel plates, spaced apart with end plates to create a gap. Coil rotor moves angularly within this gap with no magnetic attractive force between components.

Configurations:

• Type L (Low Profile): Smaller height for compact installations, reduced angular rotation per stator arc segment
• Type S (Standard): Larger height with approximately double the angular rotation per arc segment compared to Type L

Performance Specifications

Angular Range:

• TMR Series: 60° – 180° (dependent on pole configuration)
• TWR Series: Up to 90°
• Extended range available up to 360° with modified windings (requires 4 leads and commutation)

Torque Output:

• Continuous torque: Up to 1000 oz-in
• Proportional to input current magnitude

Acceleration: High angular acceleration capability due to low rotor inertia

Supply Configuration: Typically unhoused without bearings or shaft for direct mounting to customer bearing systems. Housed versions available upon request.

Advantages & Limitations

Control & Integration

Required Electronics:

• Motion controller (for programming speed, acceleration, PIDs, position)
• DC linear servo amplifier (sinusoidal or trapezoidal)
• Feedback device (rotary encoder or resolver) for closed-loop servo positioning

Control Flow:

1. Motion profile programmed on PC and downloaded to controller
2. Controller sends ±10V reference signal to servo amplifier
3. Amplifier provides current to motor based on reference signal
4. Motor moves to desired position at programmed speed/acceleration
5. Feedback device returns position data to controller 500x per second for verification

Design Flexibility

• Supplied unhoused for direct integration with customer bearing systems
• Housed configurations available upon request
• Custom angular excursions available up to 360°
• Two-lead design simplifies wiring (commutated versions require 4 leads)
• Compact length-to-diameter ratio fits applications where conventional motors cannot

Applications

Limited angle torque motors excel in precision angular positioning across multiple industries:

Aerospace: Flight control surface actuation, gimbal systems, antenna positioning

Semiconductor: Wafer handling, valve control, precise angular alignment

Medical: Surgical robotics, imaging equipment positioning, diagnostic instrument control

Military: Weapon systems, radar positioning, optical tracking

Industrial: Valve actuation, optical scanning, pick-and-place robotics

Why Choose Limited Angle Torque Motors

Limited angle torque motors provide exceptional angular acceleration with zero torque ripple in a low-profile brushless design. The direct-drive configuration eliminates backlash while delivering precise position control. Two distinct series accommodate various application requirements—TMR for higher torque density with iron core design, TWR for ultra-low inertia with moving coil architecture. Custom configurations available from 60° to 360° with torques up to 1000 oz-in.

Ordering Information

All torquers are custom-built to specification and not stocked. Available for any angular excursion up to 360° and continuous torques up to 1000 oz-in. Contact H2W Technologies with your specific angular range, torque, and envelope requirements for custom quotation.

Product Numbering Chart

![Limited angle torque motor product number chart showing TMR and TWR series designation system]

Typical Performance Curve: Torque vs. displacement for 4-pole configuration shows peak torque at center position with gradual reduction toward travel limits.