Foundations of Physical Science

Workshop: Electric Motor

Electric MotorCPO Science

Key QuestionsHow are electricity and magnetism related?

How does an electric motor work?

OverviewM a g n e ts

B u i l d a n E l e c t r i cM o to r

D e s i g n a n d B u i l dD i ff e r e n t M o to r s

Fun with MagnetsTake your motor completely

apart to expose the little ceramic magnets that are in the rotor pockets

What “stupid magnet tricks” can you come up with?

Compare force of attraction with force of repulsion

Fun with Magnets

100 20 30 40 50 60 70 80 90 100 110 120 130 140D istance in m illim eters

AttractRepel

AttractRepel

AttractRepel

distance

N-S S-S N-N

Distance 1

D istance 2

D istance 3

Slide the second m agnetcloser and closer untilthe first one m oves.

F irst m agnet

Second m agnet

S - S R e p e l

N - N R e p e l

S - N A t t r a c t

How does a motor work?

A t t r a c t

R e p e l

R o to r

M a g n e ts o n th e o u ts i d e ( s ta to r )p u s h a n d p u l l o n m a g n e ts o n th ei n s i d e ( r o to r )

ElectromagnetsCoil of wire wrapped around a steel pin

You can reverse polarity by switching direction of electricity

Electromagnets

N

N

E l e c t r i cC u r r e n t

E l e c t r i cC u r r e n t

E l e c t r o m a g n e t M o d u l e

C o i l o f W i r e

T h i ck S te e l P i n

E l e c t r i c E y e

Switching electromagnet polarityMechanism that makes electric current switch direction is called a commutator

Clear = north

Black = south

Switching electromagnet polarity

N

N

A

A

B

B

C

C

S w i tch

Rota

t i on

C l e a r = n o r th p o l e

B l a ck = s o u th p o l e

Build a 4-pole electric motor

4 a l te r n a t i n g m a g n e ts

p i n k d i s c

co n n e c t b a t te r y p a ck

h o l d th e r u n b u t to n

n u d g e to s ta r t

Design other motors Using other colored disks, decide

how to build a working motor

Save the green disk for last – it’s a bit tricky!

Use a photogate to measure frequency, and from that calculate the speed in rev per sec (frequency divided by # black areas)

Who can build the fastest motor?