Torque and force density

March 1, 2007
Packed with power. Mini but mighty. Compact housing. What do these phrases have in common? Each hints at a design optimizing torque density. At its core,

Packed with power. Mini but mighty. Compact housing. What do these phrases have in common? Each hints at a design optimizing torque density. At its core, torque density is all about getting the most power from the least amount of space. For applications where cubic inches are at a premium, consider these power-packed products and expert tips.

High torque servomotor

The DST servomotor series offers higher torque density in a 30% smaller package than previous designs; handles speeds up to 4,500 rpm and works as a direct drive in place of small gears.

Baumüller
www.baumueller.de

Hybrid stepper motor

H3 stepmotors use aluminum housing for superior heat dissipation to create high torque. Stator-enhanced magnets deliver up to 40% more torque in the same footprint as other motors, while oversized bearings handle larger-than-normal side and radial loads.

Portescap
www.portescap.com

Linear actuators

Size 8 hybrid linear actuators, now with encoder feedback, occupy a space of just 21 mm square. With thrusts up to 10 lb, these motors are well suited for applications requiring precise positioning and rapid motion.

Haydon Switch & Instrument Inc.
www.hsi-inc.com

Servo insert couplings

Torque-dense Servomax couplings feature a precision molded elastomer element press fit between two precision machined coupling halves, resulting in zero backlash and guaranteed concentricity.

R+W America
www.rw-america.com

Servo actuator

The TPM+ incorporates a high-precision gearhead, high-pole motor, and feedback in a compact package. The highly integrated actuator is 50% smaller than standard motor-gearbox combinations in terms of size as well as mass.

Wittenstein Motion Control
www.alphagear.com

DBO ✓ list

  • Think more power in less space

  • Consider smaller, stronger motors and gears

  • In motors, increase content of active materials (iron, copper, permanent magnets) to increase torque

  • Likewise, decrease content of inactive materials (air, plastic, insulation)

  • Heat is the limiting factor in electric motors with regard to torque density

  • Remember that magnets can only take so much heat; then they weaken, reducing motor torque

  • Key to torque density is current density

  • Think about coil winding design; traditional design limits use of copper inside slots on motor stators

  • Less copper means less current, less magnetic flux, and less torque

  • High slot fills mean maximum current per unit of motor circumference, creating maximum torque density

  • Consider “cut-core” stator technology with each tooth individually wound prior to motor assembly

  • Keep windings cool to improve torque density

  • Proper motor cooling (correct heat sinking and unimpeded air flow) is vital to torque density

  • Attach motor to heat sink; paint motor black; lower ambient temperature

  • Apples to apples: When comparing motor torque, look at continuous duty ratings and product lifespan

  • Consider planetary and right angle (worm, bevel, hypoid) gear sets for maximum torque density

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