Mouse-trap carsMouse-trap cars

The The designdesign PROCESS PROCESS

Objectives:Objectives:

1. To design and construct a mouse-1. To design and construct a mouse-trap car.trap car.

2. To design and use the mouse-trap as 2. To design and use the mouse-trap as the motor or power source.the motor or power source.

3. To design and construct a car that 3. To design and construct a car that will travel 20 feet.will travel 20 feet.

GuidelinesGuidelines

1. Use regular mouse-trap. No rat-traps!1. Use regular mouse-trap. No rat-traps! 2. Mouse-trap MUST be mounted on car.2. Mouse-trap MUST be mounted on car. 3. Mouse-trap car MUST travel 20 feet.3. Mouse-trap car MUST travel 20 feet. 4. MUST use at least 10 parts, but no more than 4. MUST use at least 10 parts, but no more than

20 parts.20 parts. 5. Mouse-trap car MUST start on its own power. 5. Mouse-trap car MUST start on its own power.

NO PUSHING to get it started.NO PUSHING to get it started. 6. Mouse-trap car MUST have at least 3 wheels.6. Mouse-trap car MUST have at least 3 wheels. 7. Mouse-trap car MUST use string from power 7. Mouse-trap car MUST use string from power

source. No rubber bands!source. No rubber bands!

Concepts to think about :Concepts to think about :

1.1. Friction & Resistance : How to over come them Friction & Resistance : How to over come them ??

2. Traction & Leverage : These concepts are 2. Traction & Leverage : These concepts are HUGE in solving the problem of distance and HUGE in solving the problem of distance and starting power.starting power.

3. Weight vs. Strength.3. Weight vs. Strength.

4. Craftsmanship : This concept is the difference 4. Craftsmanship : This concept is the difference between success and failure.between success and failure.

WARNING !

Your mouse-trap car must travel 20 feet!

Design considerationsDesign considerations

Fast start vs. slow and steady ?Fast start vs. slow and steady ? What is the most effective wheel ? What is the most effective wheel ?

Light or heavy ?Light or heavy ? Big or small ?Big or small ? Thick or thin ?Thick or thin ? Platinum or gold ?Platinum or gold ?

Friction ? Where is it good and where is it bad ?Friction ? Where is it good and where is it bad ? How does the mouse-trap works as a motor or How does the mouse-trap works as a motor or

power source?power source? Do you want a heavy or light car ?Do you want a heavy or light car ? Does it matter where you mount the mouse-trap on Does it matter where you mount the mouse-trap on

the car?the car? Does the car have to look pretty or cool ? Does the car have to look pretty or cool ?

Power systems in mouse-trap Power systems in mouse-trap carscars

1. 1. Potential EnergyPotential Energy : The spring (at : The spring (at rest) is the potential energy. rest) is the potential energy. What is potential energy ? What is potential energy ? – Stored energy or the ability to do work.Stored energy or the ability to do work.

2.2. Kinetic Energy Kinetic Energy : The moving spring : The moving spring is the kinetic energy.is the kinetic energy.What is Kinetic Energy ?What is Kinetic Energy ?– Energy of movement.Energy of movement.

HintsHints

1. Friction :1. Friction : The resistance to motion between 2 objects The resistance to motion between 2 objects

in contact with each other.in contact with each other.

Friction is good for wheel traction on floor.Friction is good for wheel traction on floor. Friction is bad for all moving parts that Friction is bad for all moving parts that

must work together.must work together. Good craftsmanship is the solution to the Good craftsmanship is the solution to the

problem!problem!

HintsHints2. Lever arm of mouse-trap: 2. Lever arm of mouse-trap:

By adjusting the length of the By adjusting the length of the mouse-trap’s lever arm, you mouse-trap’s lever arm, you can vary the force that is can vary the force that is applied to the wheels of your applied to the wheels of your car.car.

Long lever arms DECREASE Long lever arms DECREASE THE PULLING FORCE, WHILE THE PULLING FORCE, WHILE SHORT ARMS INCREASE THE SHORT ARMS INCREASE THE PULLING FORCE.PULLING FORCE.

HintsHints

3. TORQUE :3. TORQUE : Torque is a Torque is a

turning force.turning force.

When you turn a water When you turn a water faucet, open a door, or faucet, open a door, or tighten a wrench, you tighten a wrench, you exert a turning force.exert a turning force.Torque is very Torque is very important in getting important in getting your car to start under your car to start under its own power. No its own power. No pushing to start car.pushing to start car.

HintsHints 4. 4. Rotational Inertia :Rotational Inertia :

The property of an object to resist The property of an object to resist changes in its rotational state of motion.changes in its rotational state of motion.

The greater the distance between the bulk of The greater the distance between the bulk of an object’s mass and its axis of rotation, the an object’s mass and its axis of rotation, the greater rotational inertia.greater rotational inertia.

It follows that the greater the rotational It follows that the greater the rotational inertia of an object, the harder it is to change inertia of an object, the harder it is to change the rotational state of that object. If rotating, the rotational state of that object. If rotating, it is difficult to stop; if at rest, it is difficult to it is difficult to stop; if at rest, it is difficult to rotate.rotate.

Rotational InertiaRotational Inertia

Rotational InertiaRotational Inertia

If you use a solid wheel – Easier to change If you use a solid wheel – Easier to change rotation.rotation.Why ? Less rotational inertia because mass Why ? Less rotational inertia because mass is more evenly spread out from center of is more evenly spread out from center of wheel.wheel.

If you use a spoke wheel – Hard to change If you use a spoke wheel – Hard to change rotation.rotation.Why ? More rotational inertia because Why ? More rotational inertia because mass is concentrated on the outside, far mass is concentrated on the outside, far from center.from center.

Example of rotational inertiaExample of rotational inertia

Summary

• Have fun and use The Design Process to solve the problems.

• It is not suppose to work the first few times….don’t give up!

• There are over 55 different concepts you need to over come.

• You got to remember that craftsmanship is really important.

• Use any materials you want.

Good Luck !

• You have 3 days to brainstorm and get some sketches down on paper.

• You have 15 days to construct your mouse-trap car.

• I am not impressed that you built a mouse-trap car…..Impress me by testing your car.

• 20 feet ! No pity from me……….

Use The Design Process concept in your everyday life to solve any problem that you may encounter !