PT 2.1 - Engineering Goals

1.2   Engineering Goals & Brainstorming

Engineering Goals
To come up with a lightweight structure with big wheels at the back to ensure that our mousetrap car is able to reach the criteria given to us.

Criteria Given:
-> Come up with 3 unique mousetrap car designs that fulfils the following competition specifications:
Length = 30 cm max
Width = 15 cm max
Height = 15 cm max
-> Mousetrap car must move off from rest powered only by the drivetrain without any push/pull from student.

Testing Site:

Overview of the testing site.


Actual Testing Site @ School


The testing site is asphalt/ tarmac. The length of the distance covered by the tape is 8 meters.

Brainstorming

Design Criterions :
( For distance)
Size:  Large wheels have more prominent rotational idleness than little wheels. In viable terms, this implies once they begin rolling, they're harder to quit rolling. This makes extensive wheels ideal for separation based challenges — hypothetically, they'll quicken less rapidly than little wheels, yet they'll move much longer and they'll travel a more prominent separation in general. Along these lines, for most extreme separation, make the wheels on the drive hub (the one the mousetrap is fixed to, which is typically the back one) very large.

The weight of the wheels: Any unnecessary weight will ultimately slow the car down or lead to added friction. In addition, it's worth noting that wide wheels can even have a small negative effect on the car's drag due to air resistance. For these reasons, we want to use the thinnest, lightest wheels available for the car.

Axle: Assuming the car is a back-wheel drive car, each time the back axle turns, the rear wheels turn too. If the back axle is thin to a great degree, the mousetrap car will be able to turn more times for the same length than if it were more extensive. For this reason, we will be making our axle out of the skinniest material available but one that can still support the weight of the frame and the wheels. ** Best choice would be a lubricated metal rod.

Friction: Should there be no friction against the ground, the mousetrap would be making the axle turn without gaining extra distance. Thus, it would be sensible to create traction by giving the edges of the wheels friction.

The weight of the frame: The weight of the frame has to be as light as possible. Any extra weight will cause the car to travel a shorter distance.

Design Criterions:
( For speed)

Increasing acceleration
Shorten the lever arm: Installing a shorter lever arm is the best way to adapt a racer for speed. However, if the lever is too short, it will spin out.

Smaller wheels: Smaller wheels is easier to turn. So make the front wheels as small as possible. A good standard is approximately 3 inches in diameter. Use materials that are as lightweight as possible.

Increase size of axle: The greater the ratio of the diameter of the axle to the wheels, less force will be required to accelerate the car. In other words, to increase acceleration, a larger axle should be matched with a smaller wheel.

Increase traction: In order to pick up speed, the wheel needs to create pressure against the ground. Use a rough texture around the outside to give the wheel traction. Example; rubber balloon.

Reducing Air Resistance
Reduce weight: Reducing the weight will lower rolling friction with the ground. Trim the deck down so it is only as large as necessary to support the mousetrap. When gluing down the deck, put it as close to the back wheels as possible without touching them.

Designs

Design 1:
Design Explanation :

This design of the care includes large styrofoam wheels, a thin axel and a wooden frame. The large styrofoam wheels allows more distance to be covered as compared to a smaller wheel per axle turn. The usage of a thinner axle allows each turn to happen faster as compared to if a thick axle is connected. The mousetrap which is placed right in the middle of the thick wooden frame makes the whole car stable. Granted the usage of the wooden frame increases the weight of the car and thus slows down the distance the car travels.

Design 2:

Design Explanation :
This car design consists of a small styrofoam wheel, a thick axle and a wooden block as the frame of the car. The small styrofoam wheels is light thus decreasing the light of the whole car. The thick axle is more stable and thus will not snap as easily as if a thin axle is used. The wooden frame, however, does add some weight to the car.

Design 3:

Design Explanation:

An extended lever, light structure, large styrofoam wheels and a thin axle make up the structure of this car design. The extended level increases the amount of tension of the string, thus allowing the car to travel a longer distance. The large styrofoam wheels, which are extremely light, allows the car to travel a longer distance. The usage of a thin axle as compared to a thick axle allows more for more turns and thus allows the car to travel a longer distance. Overall, the whole structure is very light and thus the best out of the 3 designs.

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