Additional
Advanced Construction
Tips
K*bot
World Championships®
Made with K’NEX
Parts
If
you like to build
robots remember you
must first learn the
science behind
building them which
involves mechanical
robotic engineering.
This might sound
challenging,
complicated, or even
difficult. However,
if you want to learn
how k*bot robots
work it can be a lot
of fun as well as
teach you how things
work so you can have
a mechanical
advantage when
competing with other
K*bot builders at
this camp. This
starter booklet will
help you understand
how to get started.
 
The pure fun of
learning combined
with hands-on
building of our
K*bots will provide
you with tools from
learning simple
machine tools and
robotic design
technology that is
important to your
problem-solving
skills in life. You
will be provided
with a K*bot camp
checklist of things
that need to be
checked and
completed with your
K*bot on the first
day of camp.
Unit 1
We will look at how
to build a frame for
your robot and
how
forces are
transferred between
the different parts
of a K*bot’s
construction during
K*bot competition.
First
let’s look at
General K*bot Frame
or Chassis Designs &
Construction
A student of K*bot
design must make
competition
adjustments with
their K*bot made
with K’NEX parts to
find the right
combination for
success. Even at the
K*bot World
Championships held
in Las Vegas we have
found that some
students have
difficulty building
structurally sound
K*bot frames
(chassis). Students
often do not have a
complete
understanding of how
to build or utilize
gear reduction and
other mechanical
advantages to build
a K*bot for power
and durability for
competition. If you
listen to the
instructors they
will help you start
to understand how to
construct, evaluate,
and compare various
K*bot frame designs.
Sharing K*bot
information on your
design features,
advantages, and
disadvantages with
classmates will
prove to be valuable
for all the students
in the camp.
K*bots must be
designed to be
strong and sturdy.
The frame of a K*bot
is like a playhouse
you might build in
the backyard. If a
mild wind blows the
playhouse down and
it falls apart your
playhouse did not
have a strong enough
frame construction
to hold it up. The
power of your K*bot
will depend on
creating “gear
reduction” which
will make your K*bot
stronger. The
stronger K*bot frame
and gear reduction
will allow the
maximum amount of
pressure to be
exerted onto the
wheels to push to
the K*bot.
Designing K*bot
Frame Structures
Beams, Columns,
Frames, Joints
-
K’NEX parts require
maintaining close
tolerances when
manufactured so that
the connecting
mechanisms will
function properly.
Internal loads
generated within
mechanisms also need
to be considered. K*bot
frame construction
rods may deflect
primarily by
bending. A straight
rod will curve
slightly under
bending load. The
amount of curvature
is proportional to
the K*bot moment
load.
K*bot
structural systems
are built of
elements such as
rods and connectors.
Beams in buildings
support vertical
load due to weight
on a floor or roof.
Columns are the
vertical posts that
hold up the beams in
buildings. The
monumental temples
of ancient Egypt
and Greece had stone
columns to support
stone beams. As a
rule, K*bot weight
bearing joints
(connectors) should
be carefully
considered in all K*bot
designs where weight
is critical. Where
necessary, you
should place weight
bearing connectors
in strategic
structural positions
to maximize the K*bot’s
strength and
stiffness bonding
for K*bot
competition. K*bots
which are not
structurally well
built could deform
under the heavy load
of another K*bot
during competition.
If your K*bot bends
during Division K*bot
competition loads
you may decide to do
a K*bot deformation
analysis. Just take
each of the K*bot
elements of the
system and consider
them separately.
These separate K*bot
elements are called
free K*bot bodies.
Take a look
the 2004 Division 1
K*bot World Champion
Snow Plow above and
how everything
connected eventually
ends up connected to
the wheels. You
don’t see parts
connected to the
wheels with just
simply 2 K’NEX rods.
On the contrary you
see everything
equally balanced.
You also want to
avoid what might be
referred to as a
swivel frame. These
types of frame
designs have fallen
victim to improper
weight management
and are too long and
get caught on their
sides during
competition. This
type of frame design
often will turn
their K*bot sideways
in a match, allowing
the challenger a
victory. Where you
put your wheels
(wheel positioning)
and how you place
parts over your K*bot
(weight management)
are essential when
considering frame
(chassis) designs.
This is one of the
most popular
mistakes that new K*bot
students make with
gear reduction.
Granted in a gear
reduction robot you
have power, but the
only way to make
sure that the power
is exerted onto the
wheels is with the
correct weight
distribution onto
the wheels. A gear
reduction K*bot is
apparently slower
than a non-gear
reduction K*bot, so
you cannot waste
time sliding around
the competition
arena. Out of the
total weight of your
K*bot which is 3
pounds maximum your
weight should be
only 2/3 over the
power wheels and
only 1/3 over the
front of the K*bot.
You could go
with most all your
weight on your back
wheels, but that
gives you a
weakness. The
leverage would be in
favor of your
opponent.
 
For example:
if your opponent has
2/3 of their weight
on the power wheels
and 1/3 on the front
ramp and you have
most of your weight
over the power
wheels towards the
back of the K*bot
then occasionally
both K*bots may be
lifted into the air
during the match.
However, you will
tumble down first
because you will
have more weight
from the other K*bot
propelling you
backwards. This is
an important factor
which may determine
the winner during a
match. The division
of the weight into
thirds gives you a
pound of frontal
weight that disables
your opponent from
pushing you up. In
general you don’t
have to worry about
sliding wheels
because you are so
heavy over the power
wheels, unless you
have a swivel frame
that must be changed
to stabilize the
problem.
Now let’s look at
parts of (elements)
which determine K*bot
Mechanics
K*bot mechanics is
about how forces are
transferred between
the different parts
of a K*bot’s
construction during
K*bot competition.
Mechanics helps keep
a K*bot in balance.
Although you could
build a K*bot
without knowing
anything about
mechanics, it will
help in preventing
your K*bot from
tipping over when
turning or when
lifting up another
K*bot during
competition. Another
point where
mechanics pays off
is in the axles. On
small robots you can
attach the wheels
directly to the
output shaft of the
motor; however this
doesn't work well
for larger robots as
this puts a lot of
stress on the
internal parts of
the motor. A better
way is to provide an
axle to attach the
wheel to and some
gears to connect the
motor to the axle.
Knowledge of K*bot
mechanics allows
intermediate and
advance students to
design essential
components such as
gear reduction and
the powerful double
gear reduction used
by many of the top
Division 1 and 2
K*bots in the world
today.
Unit
2
The K*bot balancing
act: What is center
of gravity
Objective:
Study the physics
involved in the
balance of a K*bot
during competition.
Students who design
competition K*bot's
must address a
variety of physical
considerations in
their design,
including the center
of the K*bots mass.
Gravity is an
invisible force of
attraction between
two objects.
Everything with mass
has gravity. As the
Earth is pulling
your K*bot down to
it, your K*bot is
pulling up on it.
Your K*bot will pull
with much less force
because gravity is
proportional to
mass.
The
center of mass of
your K*bot is the
point at which the
whole weight of the
K*bot balances. The
center of mass of
the K*bot might be
considered the
"average" point of
all the matter in
the K*bot. You can
calculate the pull
of two objects with
this formula:
Force of
Gravity = Mass of
Object 1 x Mass of
Object 2
Gravitational
Constant x Distance
between Objects.
In order to
apply the laws of
mechanics to a
particular body
scientists generally
try to consider it
as a free body—they
isolate the body
from its larger
environment and
consider only the
forces acting on
that body. This
simplifies the
situation by
excluding extraneous
forces and
influences that are
not relevant to the
problem. When
gravity is pulling
one object to
another, the force
has to have
direction. It
usually pulls to the
center of the mass.
In a sphere shape
(like earth) this
point is in the
center of the
sphere. That is said
to be the center of
gravity. Let’s
imagine that a small
K*bot is on one side
of a seesaw and a
large K*bot is on
the other side of
the seesaw. The
balance point of the
seesaw is not in the
middle of it,
otherwise it would
balance and the weight of the small
K*bot and the large
K*bot would be
equal.
We know the large K*bot
easily exerts more
force downward
(weighs more) than
the small K*bot. If
you move the pivot
point of the seesaw
toward the large K*bot
they will balance
out (eventually).
All together, the
small K*bot, the
large K*bot, and the
seesaw's center of
gravity is roughly
where the pivot
point of the seesaw
is pivoting.
You're probably
not aware of it, but
adjustments when you
move the K*bot
affect the center of
gravity. Tightrope
walkers, for
example, adjust
their arms, hips and
other body parts in
order to move their
center of gravity
and stay atop the
rope.
For an average
uniformly shaped K*bot,
there is a simple
mechanical way to
determine the center
of gravity. If you
just balance the K*bot
using a string, the
point at which the
K*bot is balanced is
the center of
gravity. If the
object is then
shifted a measured
distance away from
the center of mass
and again balanced
by hanging a known
mass on the other
side of the pivot
point, the unknown
mass of the object
can be determined by
balancing the
torques. The mass of
an object is a
fundamental property
of the object; a
numerical measure of
its inertia (a
property matter by
which it remains at
rest or in uniform
motion in the same
straight line unless
acted upon by some
external force); a
fundamental measure
of the amount of
matter in the
object. The weight
of an object is the
force of
gravity
on the object and
may be defined as
the mass times the
acceleration of
gravity.
Unit 3
Influences
which cause changes
in the motion
The
influences which
cause changes in the
motion of your K*bot
are forces and
torques.
However, if the
point of action of
one of the forces is
moved off the line
of action, the
result is a torque.
Torque
is two equal and
opposite forces
passing through the
same point (on the
same line of action)
will cancel each
other out. This
torque is called a
couple or moment.
All three terms
(moment, torque, and
couple) are
equivalent in
meaning, but there
are language
conventions for
their use. Torque
usually refers to
moment with its axis
aligned with that of
a shaft. The term
“couple” usually
refers to moment due
to equal and
opposite forces
separated by a
distance. The
effects of forces on
objects are
described by
Newton's Laws. A
force may be defined
as any influence
which tends to
change the motion of
an object. The
relationship between
force, mass, and
acceleration is
given by Newton's
Second Law. The
relationship between
the external
torque
and the
angular acceleration
is of the same form
as
Newton's second law
and is sometimes
called Newton's
second law for
rotation. The
rotational equation
is limited to
rotation about a
single
principal axis,
which in simple
cases is an axis of
symmetry. Newton’s
First Law states
that an object will
continue at rest or
in motion in a
straight line at
constant velocity
unless acted upon by
an external force.
Newton's Third Law
states that all
forces in nature
occur in pairs of
forces which are
equal in magnitude
and opposite in
direction.
A
“force” is a push or
a pull or an
interaction between
two objects. If
there aren't two (or
more) objects there
cannot be a force.
The objects don't
necessarily have to
touch, e.g. gravity,
electromagnetic and
electrostatic
forces. A force is
represented by a
vector: the
magnitude represents
the magnitude of the
force; the direction
represents the
direction in which
the force acts; the
origin defines where
the forces act on
the object. Forces
can cause things to
move, bend, or
break. The weight of
an object is a force
downward toward the
center of the Earth
caused by the
acceleration of
gravity. Impact
forces are caused by
the sudden
deceleration of a
thrown or moving
object. Centrifugal
forces are caused by
the acceleration of
a moving and turning
object. Force is
measured in units of Newtons (N) in the
international system
(SI) and in units of
pounds (lb)
in the English and United States (USCS)
systems. Force
distributed over an
area is pressure,
and conversely,
pressure on an area
results in a force.
If you push on a
door to open it the
area of contact of
your hand
distributes the
force of the push
into a pressure over
the area of contact.
The dynamics of
pushing the door
open are simplified
if we consider the
push as acting on a
single point within
the area of contact.
The magnitude of the
force tells us how
much force is
applied. The
direction is the
particular line of
action of the force.
Unit
4
What is Friction and
how will it help my K*bot
Friction
is a force that resists
sliding motion and is
always in a direction
opposite to the sliding
motion or applied force.
The amount of friction
is proportional to the
force holding two
surfaces in contact and
depends on the materials
of the two surfaces.
This is called Coulomb
friction, after the
scientist who developed
this mathematical
relationship. Coulomb (koo~lam)
friction does not depend
on the area of contact,
only the force pressing
the two surfaces
together. For example,
metal sliding on ice has
a very low coefficient
(contributing factor) of
friction (m), and rubber
on asphalt has a fairly
high coefficient
(contributing factor) of
friction. If you are
driving a car on ice,
getting wider tires
won’t help you. You need
to change the properties
of the tires such as
putting metal studs in
them or adding chains.
Frictional force is the
force of compression
between the two
materials and the
coefficient
(contributing factor) of
friction. The
contributing factor of
friction has two
groupings, static (fixed
position) and dynamic
(active). Generally, the
contributing factor of
static (fixed position)
friction is higher than
the contributing factor
of sliding friction.
That’s why a car will
stop faster if the
brakes are controlled so
that the tires don’t
slip.
Traction friction
concerns the ability of
a tire to start, stop,
and not skid sideways or
backwards.
Automobile tires have
treads to improve their
traction and decrease
the chances of a skid.
The treads are shaped
differently for various
weather conditions. K*bot
tires don't have treads
when using K*bot
competition rubber bands
which use the adhesive
properties of the rubber
for their traction.
Instead of standard
K’NEX tires, K*bots use
Alliance rubber bands
over the tires that are
soft and almost sticky
to the competition
rubber surface. This is
a form of molecular
friction, and it is
related to the surface
area on the competition
table. When a K*bot
slides during
competition, it is more
controlled with this
type of tire than a tire
with treads, which may
skid more frequently.
The warmer the K*bot
tire gets, the better
its traction. Even
though the blocks look
smooth, they are actually quite
rough at the microscopic
level. When you set the
block down on the table,
the little peaks and
valleys get squished
together, and some of
them may actually weld
together. The weight of
the heavier block causes
it to squish together
more, so it is even
harder to slide.
Different
materials have different
microscopic structures.
It is harder to slide
rubber against rubber
than it is to slide
steel against steel. The
type of material
determines the
contributing factor of
friction, the ratio of
the force required to
slide the K*bot to the
K*bot’s weight. If the
coefficient
(contributing factor)
were 1.0 for example,
then it would take 2
pounds of force to slide
the 2-pound K*bot, or 3
pounds of force to slide
the 3-pound K*bot. If
the coefficient were
0.1, then it would take
two tenths of one pound
of force to slide the
2-pound K*bot. So the
amount of force it takes
to move a K*bot is
proportional to that K*bot’s
weight. The more weight,
the more force required.
Advance thinking that rougher surfaces experience more friction sounds safe
enough - two pieces of
coarse sandpaper will
obviously be harder to
move relative to each
other than two pieces of
fine sandpaper. But if
two pieces of flat metal
are made progressively
smoother, you will reach
a point where the
resistance to relative
movement increases. If
you make them very flat
and smooth, and remove
all surface contaminants
in a vacuum, the smooth
flat surfaces will
actually adhere to each
other, making what is
called a "cold weld".
Once you reach a certain
degree of mechanical
smoothness, the
frictional resistance is
found to depend on the
nature of the molecular
forces in the area of
contact, so that
substances of comparable
"smoothness" can have
significantly different
coefficients
(contributing factor) of
friction. When
coefficients of friction
are quoted for specific
surface combinations are
quoted, it is the
kinetic (related to or
produced by motion)
coefficient
(contributing factor)
which is generally
quoted since it is the
more reliable number.
Unit 5
K*bot speed and
acceleration, gears, and
motors
Speed in K*bot
competitions is usually
not a factor concerning
who will win a match.
Division 1 and 2 K*bots
are driven by who has
the most powerful and
well constructed K*bot.
For example, It will
help to a certain extent
the K*bots tire rotation
movement to have the
small blue or silver
K”NEX washers between
the K*bot frame and the
moving tire on the shaft
of your K*bot. Division
1 and 2 are power
Divisions. To be
successful in these two
Divisions you will need
to understand how gear
reduction works.
Gears provide the most
efficient power
transmission with the
greatest power to weight
ratio. Most cars and
trucks have internal
combustion engines
utilize gears for the
transmission of power
from the engine to the
wheels. One of our
advanced students
in Division 2
created a
gear change initiated
transmission
which went from non-gear
reduction to double gear
reduction when it
confronted the pressure
from the other K*bot
during competition.
Gear reduction is used
on K*bots and involves
using gears of two
different sizes to work
together. Because they
are of differing gear
sizes they will have a
different distance
around the outer edge.
Let's first look at a 2
inch
circumference
diameter gear attached
to the tire rod shaft.
Roll your 2 inch gear
for one complete
revolution on a flat
surface. You will see
that the distance
covered in one
revolution is equal to
the circumference of the
gear. A gear that is
twice the size of
another in diameter will
cover the same
distance as the larger
gear when it has
completed 2 full
revolutions. The smaller
1 inch gear attached to
the motor rod shaft has
to spin twice whereas
the big gear attached to
the tire rod shaft only
has to spin once.
In
other words the input
rod shaft has to spin 2
times to get the output
rod shaft to spin 1
time. Thus we get a 2 to
1 gear ratio more
commonly written as 2:1.
A configuration like
this is referred to as a
single stage reduction
because there is only a
single interaction
between two gears. This
gear reduction will
increase the power to
weight ratio of your K*bot
but will reduce the
speed of your K*bot
during competition.
There are different
areas of K*bot design
that could benefit from
designing a single or
double gear reduction K*bot.
There
are also multi-staged
reductions which involve
many gears. How can you
determine which and how
many gears to use? Gears
can be understood
because they have
several teeth. If you
have a small blue K'NEX
input gear with 14 teeth
on it (see below) and a
larger K'NEX yellow
output gear with 34
teeth (see below), then
the 14 tooth gear will
have to rotate about 2.2
times (34/14) to get the
34 tooth gear to spin
once. Therefore we have
a 2.2:1 single stage
reduction. If you repeat
this twice as in the K*bot
above you will have a
4.4:1 double stage
reduction K*bot. The K*bot
drive train consists of
a 3 volt DC electric
motor connected to a
K’NEX rod.
What are the advantages
and disadvantages of
gear reduction?
Disadvantage, you lose
speed. The advantage of
gear reduction is
greater power to weight
ratio.
Division 1 or 2 K*bots
have a Direct current
(DC) Motor (K’NEX #
92880 red motor. Most
DC motors at normal
operating voltages spin
at over 1,000
revolutions per minute.
The red # 92880 K'NEX
single power controller
and motor units have
been built as a toy
industry motor to run at
34 revolutions per
minute.
The spinning of the
armature within a
magnetic field induces a
voltage in the armature
windings. This induced
voltage is opposite in
direction to the
external voltage applied
to the armature, and
hence is called back
voltage or counter
electromotive force. As
the motor rotates more
rapidly, the back
voltage rises until it
is almost equal to the
applied voltage. The
current is then small
and the speed of the
motor will remain
constant as long as the
motor is performing no
mechanical work except
that which is required
to turn the armature.
However, if the motor is
under load like it would
be during a regular K*bot
competition against
another K*bot, it will
slow down.
Unit 6
Understanding how a K*bot's
wheels, axles, levers,
and incline planes work
All Divisions of K*bots
use wheels and axles to
turn or move their K*bot
during competition. A
force is applied by hand
in Division M or by
motor or motors in
Divisions 1, 2, and 3
either to turn the wheel
of a K*bot or to turn
the axle. Wheel and axle
mechanisms behave like a
rotating lever with the
center of the axle as
the fulcrum (fool~kruh~m)
(a support on which a
lever pivots) and the K*bot
wheel rim as the outer
edge of the lever. K*bot
flipper mechanisms in
Division M are pushed in
order to create movement
of a weapon. The further
the effort is from the
support on which a lever
pivots the less effort
the Division M student
will need to flip the
other K*bot, i.e., Division M
World Champion Sam Steel
from England flipping
opponent during a K*bot
match. In Division 3
most K*bots have larger
wheels which require
less effort to move
their K*bot during a
match than smaller
competition wheels. K*bot
wheels and axles behave
like a rotating levers.
For example, when the K*bot
wheel turns, the rim will
rotate a greater distance
than the axle with less
effort involved in
turning it. The axle, at
the same time is turning
a smaller distance;
however, it gains in
force what is lost in
distance moved. Force is
simply increased because
of the difference in
size between the K*bot
wheel and the axle. To
simplify things you want
your K*bot wheel to use
as little effort of force
as possible applied over
a large turning distance
and your axle to have
the smallest turning
distance with the most
powerful output force
possible for your K*bot.
Creative thinking skills
applied to K*bot design
can be applied to
changing the direction
of force on your K*bot,
i.e., creating a hand
operated vertical pulley
system in Division M to
change the direction of
another K*bot during
competition.
Unit 7
What does all this mean
when you build a K*bot
The K*bot will be more
stable if it is
structurally well built
and the center of
gravity is closer to the
object that is
attracting it (the K*bot
competition table
surface). Just because a
K*bot looks symmetrical
and even, you should
still look at the K*bot
mass and density to see
where the weight is
focused. The larger the
mass of an object the
stronger the gravity
will pull. The smaller
the base the easier for
the center of gravity to
exceed the pivot edge or
point making the object
topple over.
Ideas for stabilizing an
awkward and unbalanced
K*bot
for competition
|
Problem
|
Try to
|
Or try
|
The desired K*bot
result
|
|
The K*bot is top
heavy.
|
Move the densest
part of the K*bot
to the lowest
possible point
in the object.
|
Add weight/mass
to the bottom of
the K*bot to
help stabilize
it.
|
Lowering the
center of
gravity reduces
the distance
between the K*bot
and earth. This
increases
stability.
|
|
Weighting is as
low as it can
get but the K*bot
is still
tipping.
|
Widen the base
of the K*bot to
increase the
footprint of the
K*bot.
|
Lengthening the
K*bot base will
have the same
effect as
widening the
base.
|
Lengthening the base makes the center of gravity have to travel
further to reach
an edge in order
to cause the K*bot
to topple.
|
|
The center of
gravity is as
low as it can
get and the base
cannot be any
bigger.
|
Move weight from one side of the K*bot to the other.
|
Add weight to counteract any K*bot unbalance.
|
If the K*bot has a weight bias to one side or the other, this will help
counteract it
and make the K*bot
symmetrically
weighted.
|
For
the latest 2010 K*bot
Guidebook and general
rules on K*bots go to
kbotworld.com
K*bot
camp checklist of some
things that need
to be checked and
completed with your K*bot
#1
When you receive your
starter K*bot on the
first day
check the
voltage on your two AA
batteries in the battery
pack. Each battery
should be at least 1.47
volts. One of the K*bot
instructors will show
you how to use the
battery tester. If the
voltage is 1.46 or lower
ask the instructor for
an official battery
replacement. Batteries
checked: Yes ____No____
#2
Read the 2010 K*bot
Guidebook at
kbotworld.com
to go over all the
Division 1-2-3 and M
rules and regulations
which cover everything
from weight and size
detentions to rules and
regulations for each
Division. Yes I have
read the K*bot rules and
regulations for 2010 ___
No not to this point
____
#3
Make sure the rubber
tire bands that cover
the tires on Division 1
and 2 K*bots are in good
condition. If they are
not, replace them with
new rubber tire bands.
Yes they were replaced
___No they are okay___
#4
Make sure the tan pin
clips and blue clips
that are holding wheels,
gears, and frame
together are secure and
tight.
Yes all the clips are in
place ___ No some clips
are loose or missing to
secure parts on the K*bot ____
#5
Check your K*bot's frame
to make sure it is
stable and balanced
correctly
as mentioned
in the K*bot Student
Starter Class booklet.
If you are not sure
about the K*bot frame
have your instructor
take a look at it for
suggestions. Yes it is
stable ___ No I am
having the instructor
look at it for
suggestions ____
#6
Seven inch long black
rods should only be used
for axles and frame
structure.
Try to keep the number
of these rods to fewer
than 20 on your K*bot. Seven inch gray
rods can be also used on
your K*bot. However, try
not to use more than 20 gray rods on your K*bot.
No more than 40 seven
inch rods total can be
used on a K*bot. Yes I
checked on the number of
these seven inch rods on
my K*bot and it is under
41 ____ No I did not
check on the number at
this time ____
#7
White connector
snowflakes are used for
building the frame and
can’t be used as extra
weight or decoration on
your K*bot. If you need
extra weight on your K*bot
use as many as needed of
the large blue
connectors. Yes I have
checked my K*bot and
corrected any snowflake
related problem ____ No
my K*bot is okay
concerning snowflakes
_____
Go to
kbotworld.com and click
onto 2010 K*bot
Guidebook for Rules®
Home Page |
