SPEAKER / MOTOR PROJECT
The construction of a speaker will be worth 5% of your term work (70%). The construction of
a simple electric motor assignment will be worth 5% of your Culminating Evaluation (30%).
Each student must submit their own motor/speaker. These motors/speakers will be kept in the
class until the end of the semester. A digital photo will be taken of the motor/speaker to avoid
duplication.
Examples of the motor/speaker can be found in the physic classroom.
Cost - $0.00
Students should not to spend any money on parts. Wire is available from the school. Students
are encouraged to be resourceful by taking scrap materials that are headed for the garbage.
Specifics on Motors
The motor is to be a model of the St. Louis Motor (shown on the next page), not a
“Beakman’s motor”. Students can find other types of motors on the internet which are too easy
to construct and do not require the understanding of the mechanics of motors or the underlying
electromagnetic principles. Students are encouraged to use permanent magnets as the external
magnetic source. You do not have to purchase magnets. Classroom magnets can be used
during the test.
Specifics on Speakers
A speaker is much easier to build then a motor. However, the specifications on speakers are
difficult to match for your home audio systems. Please do not test your speakers at home – it
could damage your home audio systems.
Rubric for Motor and Speaker assignments
Below level
1
0-50%
Level 1
50-60%
Level 2
60-70%
Level 3
70-80%
Level 4
80-100%
% of
final
mark
Works
Not
assembled
Requires
significant
modification
s before it
will work
Assembled to
some
resemblance of
a working
motor/speaker
Works with a
minimal
degree of
teacher
manipulation
Works quite well with
little adjustment
required by the teacher
(speaker needs to be
heard without bending
over)
/40
Materials
rebuilt from
an old
speaker or
motor
Uses completely
recycled items.
/40
No
imagination
Contains a few
parts from old
speakers and
motors
Some
imagination
used in the
construction
Very little use
of new
material
Creativity
Uses many
parts of old
speakers and
motors
Little
imagination
used in the
construction
Well designed
Imaginative and well
designed
/20
Criteria
Due Date: Last week of classes
Closure Date: end of semester
Materials
St. Louis Motor
Example of a St. Louis Motor
Key Parts
Description of key parts
Place to input the current
Brushes must gently touch the
commutator (split ring)
Axel should rotate freely.
Armature should be properly
balanced. Decide if you want the
axel on a vertical or horizontal
plane
Commutator should be made from
a good conducting material.
Check with a battery – many
metals are coated.
Permanent magnets will be
provided
Electromagnet – review the
factors affecting the strength of an
electromagnet covered in class.
The biggest mistake made in past
is the proper wrapping of an
electromagnet. Check the
polarities once your electromagnet
is constructed before continuing.
Speaker
Cross-section of a speaker and its key parts
Description of key parts
Diaphragm (cone)– some sort of
light weight material which will
push the air as the speaker
vibrates
Voice coil – the electromagnet
which receives the continually
changing current. The voice coil
should be as light as possible
without sacrificing its magnetic
strength
Spider – an elastic material
which supports the vibration of
the voice coil and diaphragm –
either attached to the diaphragm
or voice coil
Magnet – a permanent magnet
will interact with the
electromagnet to facilitate the
vibration
Note – F = ma, Newton’s second law is a major consideration in the construction of a speaker. To work
properly, the voice coil must have a high rate of acceleration. Therefore, a large magnetic force
(interaction between the permanent magnet and the electromagnet) coupled with a small mass (voice
coil) will provide the best rates of acceleration.