torque vs. speed. general topics torque speed gear ratio
TRANSCRIPT
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
TorqueForce 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 spinningMeasured in Watts (radians -Newton-
meters/second) This relationship shows that speed
and torque are inversely relatedLess torque = more speedMore torque = less speed
Gears, Chains & SprocketsGearing 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 heatHeat and friction are usually not your friends
transmission efficiency is important
Spur gears: 90% per pairWorm 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
Fisher-Price motor
0
500
1000
1500
2000
2500
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
Torque (Nm)
Spee
d (ra
d/s)
; Po
wer
(W)
Output power, W
Speed, rad/s
407 W
Stall
Peak Efficiency Fisher-Price motor
0
10
20
30
40
50
60
70
80
90
100
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
Torque (Nm)
Eff
icie
ncy,
%
76%
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 discussedRelationship between torque and speedBasic understanding of gear ratios