1.4 Design Rationales
Chosen Design (DESIGN 1)
- The Wheels are thin and do not have much surface area in contact with the ground. Hence, with this we are able to reduce the friction opposing the motion of the car, enabling it to travel further as it requires less force to move. However, thinner wheels have less stability which will cause the wheel to wobble and lose the gained force accelerating it, greatly reducing the the distance it can travel. In order to solve this problem, we add a strap on both side to the wheel preventing it from wobbling hence our mousetrap car can travel further.
- The chassis is located below the mouse trap car. It holds the car up and is supported by the wheels. The 2 wheels on either side of the car are connected by a rod (A pair of wheels at both ends of the car). The rod is held in place by 2 hooks which are made of smooth metals. We also add oil onto the rod. Both factors help to reduce the friction opposing the motion of the rod and enable the rod to spin with minimal resistance enabling it to travel further. A string is connected from the mouse trap tip and is spin around the rod. As the mousetrap is pulled back, kinetic potential energy is stored and released when the string unwinds making all the wheels spin and hence the car move.
- Lever arm & String type. For the lever arm, we decide to use a much longer lever arm as when we have learn from our lesson about turning point. The longer the perpendicular distance between the point where force is applied and the pivot, the less amount of force is required to be applied. The string type must be strong enough to withstand the forces acting on it (Such as the pulling force of the mousetrap) without snapping.
- The axles are made of hollow plastic rods and located at the front and back ends of the base. The back axle is the rod on which the string is wound. is turned the opposite direction of the vehicle movement causing the string to wing around the axis. The lever arm line directly above the drive axles when fully wounded. We also have a Axles hook located at the centre of the rod
- Positioning of Mousetrap. For maximum performance the mouse trap needs to be positioned on the chassis so that the lever arm is directly above the drive axle. In order to find the correct placement of the mouse trap on the chassis hold down the lever arm into the fully wound position and then line-up the tip of the lever arm so that it is just reaching the drive axle. Make sure to position the mouse trap so that the lever arm travels along the center of the vehicle and does not hit anything. the mousetrap is positioned on the chassis so that the tip of the lever arm lines up with the drive axle when the mouse trap car is fully wound-up. Position the mouse trap so that its centre is the same length of the lever arm away from the drive axle
Hence, we decided to chose this design as it has potential to travel a long distance
Total Length : 29.6 cm
Total Width : 12.1 cm
Total Height : 12.1 cm
Length of wooden base : 26.9 cm
Width of wooden base : 10.3 cm
Distance between hind wheels (green) : 12.2 cm
Distance between front wheels (pink) : 11.2 cm
Distance between axles : 17.5 cm
Length of trap rod : 18.4 cm
Length of string from hind axle to trap rod : 39.2 cm
Top View Bottom View