Transcript Simple electrical engineering projects

Introduction to BADI
Engineering Year 2
For BA Design for Industry
2nd year
Simple electrical engineering
projects
Students suggestions
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Investigative ‘hands on’ exercises
Simple electricity and electrical components
Related to practical designs
Building a general appreciation of common
components and their interconnection &
use.
My Approach
• Students will be asked to work in groups to
construct a working electrical device
• Using only found material
• And demonstrate it to the class
• Students will keep a brief record of their
progress, issues and observations.
Project ideas
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Buzzer / vibrator
Weighing machine (load sensor)
Electric Thermometer
Current meter (electromagnetic)
Current meter (hot wire)
Electric generator
Motor
Battery
Electric Clock
Barograph
Seismograph
Tuneable buzzer/ vibrator
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Wind an electromagnet
Fasten a strip of springy steel near it (armature)
Make a contact to touch the free end
When the current flows the electromagnet
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pulls the steel, which
opens the contact & suspends current flow
releases the steel, which springs back
closes the contact & restores the current
How can you change the rate it buzzes at?
Weighing machine (load sensor)
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Get an electric fire element or pare down one side of a fat pencil
Arrange a brass or copper contact to it that can slide up & down
Apply a voltage from a battery across the ends of the element
The contact ‘picks off’ part of that voltage – so voltage is related
to contact position
• Use a spring to bias the contact to the zero volts end of the
element
• The output voltage will be proportional to the load
Load sensor (alternative)
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Make a buzzer
1. Use a lever arrangement to move the contact
closer to or further from the electromagnet
depending on the load, or
2. Mass sensor: attach the mass to be measured
to the armature
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The rate at which it buzzes is dependent
on the load.
Temperature measurement
• Temperature sensors on cars often use a heater
arrangement and a contact that moves depending
on the temperature.
• One arrangement is to use a bimetal disk and a
heater coil. Current flows and the heater warms
up the disk, which flips. Contact is broken and the
disk cools. The time taken for it to cool depends
on the surrounding temperature, so the average
current is a measure of temperature.
Current meter (electromagnetic)
• Wind a coil of wire (electromagnet) on a
piece of plastic tube
• Find a piece of iron or steel (a slug) that
will slide inside it.
• When a current is applied the slug will be
pulled into the tube
• Connect a string to the slug and arrange for
a pointer to indicate how strong the pull is.
Current meter (hot wire)
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Needed: resistance wire (electric fire element)
When a current passes through a wire it gets hot
When it gets hot it expands
Build a rig that will allow this (small) expansion
to be indicated by turning a needle on a dial
Electric generator
• When a magnet is moved near a coil of wire
a current is generated
• Build a rig to allow a coil to be turned near
a magnet or vice versa
• Connect a torch bulb across the ends of the
coil to show when a current flows
• Experiment with different layouts
Generator (2)
Motors and generators have similar construction.
A common feature is that they have
a part that turns, called a ROTOR; and
a part that stays still, called a STATOR
rotor
Stator
In this design the
rotor carries a coil,
and magnets are
attached to the
mounting frame
Generator (3)
• If the coil is turning the wire ends will twist.
• The current can be picked off in two
different ways
• Slip rings
• Commutator
• What difference does it make which you
use?
Generator (4)
One use of a generator is a wind turbine, often
used to keep batteries charged on a boat.
One design uses a car brake disk with magnets
mounted around the periphery. A coil is
placed near the disk and when the disk rotates
a voltage is generated
Its an ac voltage and needs to be rectified
(converted to dc) before it can be used to
charge the battery
coil
Motor
• Wind a short coil of wire onto a plastic
former that has a rod through the middle
(short axis)
• Place this between the poles of a magnet so
that it can pivot on the axle
• Pass a current through the coil (use a car
sidelight bulb to limit the current)
• The coil will move
Motor (2)
• You need to interrupt or change the direction of
the current regularly so that it keeps turning.
• How can you do this? One way is to use the
inertia of the rotor to keep the rotor spinning, and
feed current pulses to the electromagnet. There
are many ways of doing this, all based on
detecting when the rotor is at the right point for
the electromagnet to attract it to the next position.
• It’s a bit like the way a four stroke car engine
works.
Motor (3) : Don’t do this
Last year some students tried to build a motor to this design,
using an air-cored coil suspended by wire ends. Mostly
these don’t work because
• The magnetic field path through the air is too long, and
• Its hard to get the coil balance exactly neutral
• The rotor has very little inertia
Also you can’t take any power out – it wont drive anything so
its no practical use.
Battery
• When two dissimilar conductors ( metal or
carbon) are placed in an acid solution (lemon
juice, vinegar etc) a voltage is generated.
• Does the voltage depend on the strength of the
acid?
• Does it depend on the size (surface area) of the
metals?
• What easily obtainable metals work best?
• BE SAFE: DON’T USE STRONG ACIDS!
Clock
A pendulum, a pair of rotating balance
weights or a balance wheel on a spring, a
tuning fork …will all give repeatable
timing.
All you need is to keep them going by
applying a pulse at the right time.
You could use an electromagnet for this.
Read about Harrison’s clocks
Barograph or seismograph
• You need a motor to drive the paper chart –
either a strip or a circle. Use a ready made
geared motor.
• Now you need to adapt this chart to record
(with a pen) the barometric pressure or
seismic vibrations.
• Lots of ideas on the web
General Resources
• http://scitoys.com/
• http://www.howstuffworks.com/
• http://www.skillbank.co.uk/
For course notes useful links etc.