Transcript Fluid Dynamics: Thrust Lesson 9 Dr. Aaron P. Wemhoff

Motors
Lesson 9
Thinking About Motors
 What

Device that converts energy into mechanical
motion
 What

is a motor?
are motors used for?
Hard drives, disk drives, fans, DVD players etc..
 How
do motors work?
Magnets- Necessary Component of Motors

History



Named for a region in Asia Minor called Magnesia
Magnesia was the first location magnetic rocks were
found
Earliest Uses- 11th Century China


Compass needles
Needle is made of a magnet that points towards the
north pole
How Magnets Work
 Magnets

Attract
Metals: iron, nickel cobalt
 Why?

Alignment of atomic structure of material
Magnetic Poles
 Magnets


North pole- attracts south pole, repels north
South pole- attracts north pole, repels south
 Easy


have two poles
way to determine north vs. south pole
Hold a compass next to a magnet
The compass needle will point to the south pole
Mechanical Motion from Electricity
 Hans

Christian Oersted
Discovered relationship in 1800’s between:
• Mechanical Force
• Magnetism
• Electricity

Followed up by Maxwell, Farady and Lorentz
Mechanical Motion from Electricity
 Basis

for Electric Motor
A wire conducting current will experience a
force when it is placed in a magnetic field
F = iL x B


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

F (Force)
i (Current)
L (Length of Conductor)
x (Cross Product)
B (Magnetic Field Strength)
Mechanical Motion from Electricity
 Vectors

Vectors represent a quantity with a size and
direction
 According



to the formula:
The force is a cross product of the vectors B
and iL
Cross Product: takes two vectors B and iL and
produces a third: BiLsin(Ө)
We will only consider vectors at right angles:
F= iLB
Mechanical Motion from Electricity
Right Hand Rule




Used to find the direction of the force on the wire
Point hand with open palm in direction of first
vector in the cross product (iL)
Close fingers in the direction of second vector (B)
Your thumb is now pointing in direction of F
Practice the Right Hand Rule!!!
Inside a Motor

Force on current (i) in a magnetic field can be turned
into torque




Simple: run current through a loop of wire in a magnetic
field
Current switches direction based on what side of the loop it
is on
Results in a pair of forces which cause torque
The loop will align with the magnets but will not spin
How Does a Motor Spin?

Add physical components to make current change
direction



Brushes: attached to power source, do not move
Commutator: attached to the coil , spins with coil
When commutator spins , brushes change direction
which results in current switching direction
 The torque will increase with more coils
A Motor in Pieces