real electric motors work
“Conventional” DC motors
are plenty of these in the average household, lurking inside
battery powered toys, the cassette player, cordless drill
and electric toothbrush. Inside a car, everything from the
cooling fan to the windscreen wipers will have a DC motor.
In fact, a luxury car with electric headlight washers, electric
seat adjustment and remote rear-vision mirrors has more
electric motors than you can poke a stick at – an
interesting competition is to simply to count them and see
who can find the most!
• Reasonably inexpensive
• Easy to control
• Brushes eventually wear out
• Brushes create electrical interference
• Brushes are bad
DC motors look something like this. This particular one
is beautifully made and probably cost at lost of money.
that won't stop us taking it apart.
at the left we have the end cap and the two carbon brushes
that contact the commutator, then the rotor, the stator
casing and its two C-shaped permanent magnets, the gearbox
housing, a little gear-wheel that fell out of somewhere,
and the gear-head and output shaft.
two brushes are solid blocks of graphite, and are pressed
against the commutator by the two small coil springs (situated
slightly anticlockwise of the brushes). The orange disc
is a capacitor that is directly across the power supply
to the motor and helps to reduce radio interference caused
by sparking where the brushes contact the commutator.
rotor is very simple…
goes in an equally simple housing with two “C”
shaped magnets. The housing is made of soft iron and creates
the magnetic poles of the stator.
best thing about this motor is the multi-stage planetary
gearbox on the end!