1. Planning

1.1 ENGINEERING DESIGN    

DEEP DIVE VIDEOS

1. 1. What was the problem the engineers at IDEO were asked to solve?

They were tasked to completely redesign the whole shopping cart.

2. 2. Name two constraints that they had to deal with.

They only had five days to design and build the prototype

They had quite a few problems, to solve and they had a lot of ideas. So they had to choose the right solutions and the main problems to solve. The had to choose a solution to be built within a day.

3. 3. What were two of the major concerns/issues the teams discovered from their research?

Safety & the shoppers will have a communication device on the cart to communicate with the staff in the store to know where the items they are searching for is.

4. 4. IDEO uses several methods, processes and ideas to generate alternative solutions.  What two principles or approaches appealed to you the most? Why?

Instead of trying out the current product and wasting time experiencing it by ourself, IDEO asks the user of the current product what they feel about the product how it can be improved. To speed up the process of generating a focus point for the problem, the team splits up into smaller groups to focus on a problem. Then later they will be asked to present their problems and try to give a solution to the problem.

5. 5. How were the possible solutions prototyped and tested?

They had 2 possible solutions. So they created the prototype and went to the supermarkets and interviewed the staffs there about their opinions about this innovation.

6. 6. Was there a redesign step in the IDEO project? What was the final outcome?

Yes there was a redesign step. The final outcome were made of the best aspects of the prototypes made. The final cart had a hand basket where you can remove from the cart to move into smaller spaces to get an item and get out of the area to go back to the cart. Not only that the cart can move side ways too. Makes it much more comfortable to use. The carts won’t get stolen too, as the carts will be useless when it doesn’t have a basket to carry items.

1.2 ASSIGNMENT OF ROLES

Project manager: Gabriel

Drivetrain Engineer: Jordan

Wheel Engineer: Alyssa

Chassis Engineer: Hamidshah

1.3 BRAINSTORMING

Engineering Goals

Develop a MouseTrap Car with the following specifications:

1. Uses only the MouseTrap provided as the only energy source
2. Has a maximum length of 30 cm, with of 10 cm, and a height of 10 cm
3. Can travel a minimum distance of 5 meters carrying an egg (the egg will be provided by the teacher)
4. All time-lines have to be adhered

1st Idea Usage of an Escapement. It uses the inertia of weights on a pendulum to regulate the release of the spring. (escapement not really drawn to scale)

2nd Idea Usage of low gear ratio It uses a low gear ratio to allow the car to move at high speeds and to regulate the release of the spring through high amounts of resistance caused by the low gear ratio.

3rd Idea A longer lever placed such that there is more forced applied at the start to overcome inertia and static friction and a higher speed as the mousetrap unwinds.

1.3.1

Scientific Concepts to consider.

There are some important scientific concepts involved in building a mousetrap car

we’ll consider a few of them here:

Potential Energy	Energy that is stored within an object, not in motion but capable of becoming active ☞ There is stored potential energy (in the spring) when your mouse trap is set and ready to be released
Kinetic Energy	Energy that a body possesses as a result of its motion ☞ Potential energy becomes kinetic energy as Potential energy becomes kinetic energy as the mousetrap car begins to move ☞ Some of this energy goes to friction– the rest makes the car go.
Force	An action that causes a mass to accelerate ☞ To change the motion of the mousetrap car, a force must be applied ☞ To increase the acceleration of the car, there needs to be an increase in the force or decrease the mass (Newton’s Second Law)
Friction	The force that opposes the relative motion of two surfaces in contact ☞ Friction will slow and eventually causes the mousetrap car to come to a stop. ☞ Friction occurs between the wheels and the floor and between the axle and the chassis between the axle and the chassis
Torque	Can informally be thought of as " rotational force" or "angular force" that causes a change in rotational motion ☞  In the mousetrap car, the snapper arm applies a force to the drive axle through the pulling string. This in turn causes a torque to be produced around the driven axle.
Power	The rate at which work is done or energy is used ☞  In a mousetrap car, the same overall amount of In a mousetrap car, the same overall amount of energy is used regardless of its speed – only the rate of use changes ☞  For distance, you want to use energy slowly (energy you want to use energy slowly (energy goes into distance instead of speed) ☞  For power, you want to use it more quickly (lots of energy needed at the start to get the car moving up energy needed at the start to get the car moving up the ramp) ☞  For accuracy, a balance is important (enough power to reach the target, but not a lot of energy saved for the end so braking will be easier)

Points of Discussion:

Topic	Discussion
Weight of the Car	In general, we want to build the lightest possible vehicle ☞ Lighter vehicles will require less force to begin moving and will experience less friction than heavier vehicles However, if the car is too light, it will not have enough traction ☞ This will cause the wheels will spin out as soon as the trap is released
Regarding Gear Ratio of Car	The trick is to have the mousetrap go off slowly (the longer it takes for the bar to shut, the longer the wheels will be in sustained movement) Hence the car should be geared to torque.
Ways to make the car go further	Extend the bar on the mouse trap using wire/dowel so that there is more distance covered by the bar (ie. it will pull a longer string; therefore causing more rotations of the axle).
Traction of wheels	Create traction by covering the wheels with tape, rubber bands, or balloons. If they are slippery, energy is being wasted. Adding tape to the rear axle may reduce slippage of the string.
Wheel to axle ratio	For distance cars, a large wheel to axle ratio would be ideal. ☞  A large wheel with a smaller axle will cover more distance each time the axle turns. For high-velocity cars, a smaller wheel to axle ratio would be suitable. ☞ Increasing the size of the axle will decrease the wheel-to-axle ratio ☞  This will increase the torque and give you more pulling force for every turn of the wheel.
Size of wheel	For distance cars, larger wheels will cover more distance per rotation than smaller wheels. For high-velocity cars, make sure the wheels have good traction so they don’t slip ☞ Traction in this case is a good type of friction! type of friction! ☞ You can increase traction by covering the edges of the wheel with a rubber band or the middle of a balloon Wheel alignment is very important. ☞ If the wheels are misaligned, the car will be working against itself – and energy will be lost ☞ In the most visible sense, misaligned wheels also mean the car won’t go in the desired direction. Misaligned wheels, over time, can cause the car to leave the track. Although the wheels are usually the cause of misalignment, string tension can also be the culprit of the car not travelling straight.
Length of the Hammer and String	Long hammer and short hammers release the same amount of energy. ☞ The difference lies in the rate at which the energy is released (power output). For long distance cars, a longer hammer would be ideal. Longer hammers provide less force but allow the car to travel a longer distance. ☞ With a longer hammer, more string would be pulled off the axle. ☞ This will cause the wheel to rotate more times, allowing the vehicle to travel a longer distance. For high velocity cars, larger amounts of energy must be released in a shorter amount of time like a sprint.

1.4 Decision Making Matrix

Criteria	Weight	Size/Shape	Appearance	Time to produce	Cost    to produce	Ease of use	Availability of materials	Environmental Impact	Safety	Row Total	Normalised Value (3 DP)
Weight		3	4	1	4	3	0	3	1	19	0.132
Shape/Size	1		4	1	4	3	0	4	0	17	0.118
Appearance	0	0		0	4	4	0	4	0	12	0.083
Time to produce	3	3	4		4	4	4	4	0	26	0.180
Cost to produce	0	0	0	0		3	0	0	0	3	0.021
Ease of use	1	1	0	0	1		0	4	0	7	0.049
Availability of materials	4	4	4	0	4	4		4	0	24	0.167
Environmental Impact	1	0	0	0	4	0	0		0	5	0.035
Safety	3	4	4	4	4	4	4	4		31	0.215
Column Total										144	1.000

Criteria	Normal Priority Value	Design Idea #1		Design Idea #2		Design Idea #3
weight	0.132	1/4	0.132	2/4	0.264	3/4	0.396
size/Shape	0.118	4/4	0.472	3/4	0.354	1/4	0.118
appearance	0.083	3/4	0.249	3/4	0.249	1/4	0.083
time to produce	0.180	0/4	0	2/4	0.360	3/4	0.540
cost to produce	0.021	2/4	0.042	3/4	0.063	4/4	0.084
ease of use	0.049	4/4	0.196	3/4	0.147	3/4	0.147
availability of materials	0.167	1/4	0.167	3/4	0.501	4/4	0.668
environmental impact	0.035	2/4	0.140	2/4	0.140	3/4	0.105
safety	0.215	4/4	0.860	2/4	0.430	4/4	0.860
	Total		2.258		2.508		3.001

1.5 Design rationale and notes

Design Element	Rationale and Notes
Wheels	Wheels with a larger diameter will cover more distance for every rotation. However this will increase the amount of torque required to turn the wheel to overcome the car’s inertia. In addition, we need to create traction. This can be done by covering the wheels with tape, rubber bands, or balloons. If they are slippery, energy is being wasted. Adding tape to the rear axle may reduce slippage of the string.
Lever arm	The longer the lever, the less torque generated for the same amount of force. Although this will result in a longer length of string that can be spooled around the acxel, it will reduce the amount of acceleration achieved by the car.
Chassis Material	wood is light, fairly strong and quite easy to work with, reducing time spent on constructing the chassis.
Chassis Shape	Triangle. It is the strongest, most stable shape with a minimal amount of materials required.
Location of Mousetrap	Mid-rear of the vehicle, low to the ground for maximum stability. For distance cars, place the trap further from the drive axle ☞ You’ll sacrifice pulling force, but get more distance For power cars, place the trap closer to the drive axle. ☞ You’ll sacrifice distance, but get more pulling force
Axles	must be able to withstand the forces acting on it by the mousetrap
String type and attachment	Nylon fishing line. It is very strong and thin, allowing us to wind around the spool without increasing its diameter too much.

1.6 Materials used

Material	Where is it used?	Reason?
Wood (Ice-cream sticks, Disposable Chopsticks etc.)	Chassis	Strong, able to bend and flex slightly; increases strength and easy to work with.
Balsa Wood, Styrofoam, Aluminum etc.	Body	Lightweight easy to shape
CD’s, Hobby Wheels, Foam wheels etc.	Wheels	Lightweight already wheel shape or easy to form into wheels
Metal pipe, PVC Pipe, Wooden Dowel etc.	Lever/Snapper arm	Strong, able to bend and flex slightly.
Metal pipe, PVC Pipe, Wooden Dowel etc.	Axel	Strong, already cylindrical.
Fishing Line	Transmission (String)	Thin and still very strong, flexible.
Plastic bottle caps, CD’s etc.	Gearbox (Spool assembly + Gear assembly)	Round.
Glue, Ball Bearings, tape etc.	Misc.	What else can you say? Its miscellaneous.

1.7 Preliminary Sketch (Using Google Sketchup)

Key features: - Triangular chassis - Rubber on drive wheels - Spoked wheels - Lever in front of mousetrap - Teardrop shaped body - Lubrication on pivots, hubs etc.