K*bot World Championships®

Building a start-up competition Division 1  K*bot with various construction tips.  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.

 #1  Sturdy frame - 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. ). 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. A student of K*bot design must make competition adjustments over time with their K*bot made with K’NEX parts to find the right combination for success. Evaluate and compare various K*bot frame designs during K*bot testing sessions. Some frame designs have fallen victim to improper weight management and are too long.  Sharing K*bot information on your design features, advantages, and disadvantages with classmates will prove to be valuable for all the students in the class. The frame of a gear reduction k*bot must be strong and sturdy because the stronger the frame will allow the maximum amount of pressure to be exerted onto the wheels. 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 frames that have the improper weight management and are too long.  

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 frame bends during Division 1 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 bodies. 

#2   Wheel Positioning and Weight  Management    

This is one of the most popular faults of gear reductions. 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 slow, so cannot waste time sliding around the battle arena. Out of 3 pounds your weight should be 2/3 on the power drive wheels and 1/3 on the front of the K*bot. Yes, you could go with all your weight on your back wheels but that gives you a weakness. The leverage is in favor of your opponent, if they have a ramp or the same leverage as you do. Then you will both be lifted into the air, but you will tumble down first because you will have more weight propelling you backwards. This may determine the winner as your opponent, because your wheels will become useless one way or another. The division of the weight into thirds gives you a pound of frontal weight that disables your opponent from pushing you up. You don’t have to worry about sliding wheels because you are so heavy unless you have a frame that you have not fixed. Everything on the K*bot is connected and eventually ends up connected to the wheels.

 

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  frame that must be changed to stabilize the problem.

#3    The Gears and their placement on rod shaft Although some people will think Gears are the most difficult step, it really isn’t. If you follow the necessary requirements listed below, your double gear reduction should be easy to install. The basic structure you want to reach is to place two small gold gears on a single 7 inch black rod on the motor rod shaft meshing against two big yellow gears on another 7 inch black rod shaft between the motor and the actual 7 inch black wheel rod shaft. On this intermediate rod shaft between the motor and the wheels you should place another small gold gear on this rod shaft between the two large yellow gears you have already installed.  This small gold gear on the intermediate shaft will mesh with the large yellow gear you will place on the wheel rod shaft to complete double gear reduction. Make sure the tan clips have their pin inserted into each gear on each shaft rod.  You now have a double gear reduction K*bot worthy of real pushing power like low gear on your parent’s car. Your instructor will walk you through each step of this process to make sure you understand double gear reduction.

#4 Now let’s look at parts of the 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.

 #5    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*bots 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.

#6     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) that 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.

 #7   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, it is the kinetic (related to or produced by motion) coefficient (contributing factor) which is generally quoted since it is the more reliable number.

#8   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 gold K'NEX input gear with 14 teeth on it  and a larger K'NEX yellow output gear with 34 teeth 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 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.

#9 Understanding a K*bot's wheels, axles, levers, and incline planes - 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., Three time Division M World Champion Harrison Stanton is from Henderson, Nevada. Harrison was a master at  flipping opponent out of the arena 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.                                               

 #10 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 can’t be 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.

 

 

Go to kbotworld.com and click on 2014 K*bot Guidebook for Rules®   K*bot class checklist of some things that need to be checked and completed with your K*bot before you compete.

#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 2014 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 2014 ___ 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 ____                     

 

 kbotworld.com and go to 2014 K*bot Guidebook for Rules®

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