What's happening? …the science behind the
brushbot…..it is all about scientific inquiry and friction,
center of gravity, inertia, closed and open circuits
Your brushbot should crawl erratically over any smooth, flat surface and
maybe even fall over occasionally – if you're getting no movement try
bending the bristles a bit or trying a different surface. To understand how it
works, imagine holding a heavy bowling ball and taking a run-up as if to
throw it, only to have your fingers stick in the holes at the last second. You'd
probably be thrown off balance and fall flat on your face. This is called
'inertia' (Newton’s first law of motion). An object in motion will stay in
motion and an object at rest will stay at rest unless acted on by an unbalanced
force.
The unbalanced motor works in a similar way. Unbalanced by the weight, the
motor's spinning shaft makes it vibrate rapidly, in turn making the toothbrush
head shake in one direction and then back again very quickly.
Cell phone motors used to create vibration alerts in consumer electronics use
this technique. As the motor shaft spins, the weight on the shaft, being offkilter,
makes the motor, and therefore the entire pager, vibrate. A tiny motor
thinner than a pencil with an unbalanced weight is whizzing around each
time the phone rings. This vibration is transferred to the whole phone making
it all vibrate and alerting you to the call.
So why doesn't it just sit in one place and buzz? Why does it move forward?
Most toothbrush bristles are angled just like the hairs on a gecko's foot,
meaning they'll slide smoothly in one direction, but not so easily in any
other. The brushbot is thrown forward by the swinging weight and the
bristles slide along the surface a short distance. When the weight swings back
again, the bristles catch and resist moving. This way the brushbot creeps
along the surface using friction, pushing along with its bristly feet.
In some ways, your brushbot works a little like how a snake eats. Snakes
have teeth which are angled backwards, just like the bristles on the
toothbrush. Any prey they consume can move in easily.
The surface friction on which a brushbot moves will affect the behavior of
the brushbot. Practice on the surface that the brushbot will be competing on.
Friction is actually a force that appears whenever two things rub against each
other. Friction is a ’catch all’ phrase for any force opposing the relative
motion of objects in contact. Friction releases some of the energy. This
release can be in the form of noise, vibration, and energy transfer. Friction
can also transfer energy into heat energy. If you rub your hands together you
will notice that the skin on your hands warms up. Some of the energy of
motion in your hands is transferred to heat energy through the friction
process.
Brushbots fall over easily: consider where your motor and other items added
are attached in order to create a balanced system. Center of gravity is the
exact spot on an object where there is the same amount of weight on one side
of the spot as there is on the opposite side. Once you change the weight
anywhere on the object, the center of gravity changes too. The ease with
which an object can be balanced depends greatly on the location of its center
of gravity.
Some ideas for your consideration….
*Mount the motor on the end. This will convert as much vibration as possible
into axial motion.
*Mount the motor on the rear end. This tends to lift the device off the front
bristles and reduce friction.
*Mount the battery on the handle end. (Similar principle as above)
*Remove the middle bristles. This eliminates friction from unneeded center
bristles.
*Split the bristles. (Similar principle as above)
*Cut a slot in the plastic. The lightest, longest tends to move faster. (Notice
how ships are designed)
*Cut the sides of the plastic. (Similar principle as above)
*Use a tail. This will tend to convert unwanted sidewards movement into
axial motion along the track.
*Change the vibration pattern by modifying the motor shaft by an
unbalanced weight which may create more vibration, and/or slow the motor.
What's happening? …the science behind the
brushbot…..it is all about scientific inquiry and friction,
center of gravity, inertia, closed and open circuits
Your brushbot should crawl erratically over any smooth, flat surface and
maybe even fall over occasionally – if you're getting no movement try
bending the bristles a bit or trying a different surface. To understand how it
works, imagine holding a heavy bowling ball and taking a run-up as if to
throw it, only to have your fingers stick in the holes at the last second. You'd
probably be thrown off balance and fall flat on your face. This is called
'inertia' (Newton’s first law of motion). An object in motion will stay in
motion and an object at rest will stay at rest unless acted on by an unbalanced
force.
The unbalanced motor works in a similar way. Unbalanced by the weight, the
motor's spinning shaft makes it vibrate rapidly, in turn making the toothbrush
head shake in one direction and then back again very quickly.
Cell phone motors used to create vibration alerts in consumer electronics use
this technique. As the motor shaft spins, the weight on the shaft, being offkilter,
makes the motor, and therefore the entire pager, vibrate. A tiny motor
thinner than a pencil with an unbalanced weight is whizzing around each
time the phone rings. This vibration is transferred to the whole phone making
it all vibrate and alerting you to the call.
So why doesn't it just sit in one place and buzz? Why does it move forward?
Most toothbrush bristles are angled just like the hairs on a gecko's foot,
meaning they'll slide smoothly in one direction, but not so easily in any
other. The brushbot is thrown forward by the swinging weight and the
bristles slide along the surface a short distance. When the weight swings back
again, the bristles catch and resist moving. This way the brushbot creeps
along the surface using friction, pushing along with its bristly feet.
In some ways, your brushbot works a little like how a snake eats. Snakes
have teeth which are angled backwards, just like the bristles on the
toothbrush. Any prey they consume can move in easily.
The surface friction on which a brushbot moves will affect the behavior of
the brushbot. Practice on the surface that the brushbot will be competing on.
Friction is actually a force that appears whenever two things rub against each
other. Friction is a ’catch all’ phrase for any force opposing the relative
motion of objects in contact. Friction releases some of the energy. This
release can be in the form of noise, vibration, and energy transfer. Friction
can also transfer energy into heat energy. If you rub your hands together you
will notice that the skin on your hands warms up. Some of the energy of
motion in your hands is transferred to heat energy through the friction
process.
Brushbots fall over easily: consider where your motor and other items added
are attached in order to create a balanced system. Center of gravity is the
exact spot on an object where there is the same amount of weight on one side
of the spot as there is on the opposite side. Once you change the weight
anywhere on the object, the center of gravity changes too. The ease with
which an object can be balanced depends greatly on the location of its center
of gravity.
Some ideas for your consideration….
*Mount the motor on the end. This will convert as much vibration as possible
into axial motion.
*Mount the motor on the rear end. This tends to lift the device off the front
bristles and reduce friction.
*Mount the battery on the handle end. (Similar principle as above)
*Remove the middle bristles. This eliminates friction from unneeded center
bristles.
*Split the bristles. (Similar principle as above)
*Cut a slot in the plastic. The lightest, longest tends to move faster. (Notice
how ships are designed)
*Cut the sides of the plastic. (Similar principle as above)
*Use a tail. This will tend to convert unwanted sidewards movement into
axial motion along the track.
*Change the vibration pattern by modifying the motor shaft by an
unbalanced weight which may create more vibration, and/or slow the motor.
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