Torque Vs. Speed

General Topics Torque Speed Gear ratio

What is a Motor? Converts electrical or gas energy into mechanical energy Provides motion Has specifications that must be designed for Specific Applications Motor Produce more Speed or Torque Pickup Truck vs. Sports Car

Torque Force at a distance Rotational strength of a motor Measured in Newton-meters or foot-pounds  Be aware of unit conversions Speed Rotations per minute (RPM)  May be measured as radians/second

Power Power = angular velocity * torque Measures how strong and how fast a motor is spinning  Measured in Watts (radians -Newton- meters/second) This relationship shows that speed and torque are inversely related  Less torque = more speed  More torque = less speed

Gears, Chains & Sprockets Gearing can be used to change the output torque/speed Sprockets and chains can be used for same purpose  Slightly less efficiency loss See drive presentation for details

Power Loss in the Mechanism Some power from the motor is lost due to friction in the mechanism Gears, belts, cables Bearings, guides Tires, balls, or other deformable item Power loss is heat Heat and friction are usually not your friends

transmission efficiency is important Spur gears: 90% per pair Worm and gear: 10%-60% Chain: 85%-95% Rack and pinion 50%-80%

Speed vs. Torque Inversely related Review: (important concept) Stall torque -> speed = 0 Stall speed -> torque = 0 More torque -> Less speed

Max Power Max power = max output of the motor This is the power you should design for Torque at max power is half of stall torque Speed at max power is half of free speed

Peak Efficiency  Peak efficiency is about at about 1/3 – 1/6 of stall torque  Occurs at about 60% of Max Power  After max efficiency -> efficiency crashes

After this exhausting presentation … Definitions of all terms discussed Relationship between torque and speed Basic understanding of gear ratios