PT 2.2 - 3 Designs and Decision Matrix

3 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.

Design Rationale
Size of wheels:  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. 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.

Reducing of 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. 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.

Diameter of 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. 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.

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. However, 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.

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.

Evaluation Matrix

CriteriaWeightSizeAppearanceTime to produceCost to produceEase of useAvailability of materialsEnvironmental ImpactSafetyRow TotalNormalised Value
Time to produce11022220100.09
Cost to produce1101222090.08
Ease of use1101122080.07
Availability of materials1101112070.06
Environmental Impact1101111060.05
Column Total108

Design Matrix

CriteriaNormal Priority ValueDesign#1Design#2Design#3
Time to produce0.0920.1820.1840.36
Cost to produce0.0820.1620.1630.24
Ease of use0.0730.2120.1430.21
Availability of materials0.0620.1220.1240.24
Environmental Impact0.0520.120.130.15

Thus, Design number 3 was chosen

Mass of mousetrap car332 g
Mass of each front wheel29g x 2 = 58g
Mass of each back wheel23g x 2 = 46 g
Wheel diameter (Front)8.4 cm
Wheel diameter (Back)12 cm
Axle diameter0.4 cm
Length of string28 cm
Length of lever extension10 cm
Overall length30 cm
Overall width15 cm
Overall height12 cm

Personal Testing Process of the Robot

Test Run 1Test Run 2Test Run 3
Total time of test run / s5s5s6s
Total distance of test run / m2.1m4.8m6.6m
Observation 1: Was the car in steady and stable motion throughout?YesYesYes
Observation 2:
Was the car moving in a straight line mostly?
Observation 3:
Did lever and string operate smoothly as well as expected?
State 1 area for modification.We changed the lever by extending it with a wooden stickWe changed the back wheels, from the friction lego wheels to the styrofoam wheels
State rationale(s) for the above proposed modification.To increase the amount of tension in the string, resulting in more distance travelled.There was too much friction in the back wheels causing in the lost of distance travelled, so we changed it to a styrofoam wheel which has lesser friction

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