Lego Racer, Post #2

            Our final design featured a 13.9:1 gear ratio, using a slanted car bed to hold the 1 kilogram weight. Given the wheels that were available, we picked two of medium diameters and another that raised the car bed to angle it down towards the front. We believed that the angle would help the acceleration of the car – instead of the weight being positioned flat and parallel to the ground, the weight was raised and slanted. This created parallel and perpendicular components of the weight which reduced the force on the car bed and contributed to the net force pointing forward. This increase in force in the forward direction would allow the car to accelerate faster. We attempted to balance the gears to balance the entire car – three on the right, some in the middle, and a few on the right. We positioned the wheels as close to the car bed as possible, to reduce the bend in the axle which contributes to friction.

           

            The gear ratio was integral to producing a car that was able to move and the speed at which it moved at. Ours featured a 13.9:1 final gear ratio, with the use of 3 8-tooth, 2 24-tooth, and 3 40-tooth gears. We calculated our gear ratio by comparing the number of times a gear turned to however many times the following gear turned as a result.

(3/1)(5/3)(5/1)(1/3)(5/3) = 125:9

The first two ratios were intended to translate a fast speed to a torque for the 40-tooth gear through an intermediate 24-tooth gear for a better performance (the 5:1 ratio alone had been skipping some of the 40-tooth gear’s teeth). We then aimed to increase the torque by increasing the ratio, but not as much as in our third iteration (41.6:1) and not below our second (8.33:1). This resulted in our 13.9:1 gear ratio and a car that traveled 4 m in 18 seconds.

IMPROVEMENTS

            If we had more time, we would have improved our gear ratio. We began with a low ratio, which didn’t work, then jumped to a higher ratio, which worked at a slow speed. We then attempted a ratio between the two points, which worked, and at a greater speed. Had we more time, we would have tried to increase the ratio a little more to explore the effects the change causes. By observing others’ cars and results, we would aim to create our own version of a car with a gear ratio of approximately 20:1 (averaging 9 seconds). We would have liked to create a gear box with individual ratios of:

(3/1)(5/3)(5/2)(3/2) = 18.8

We would have configured the gear train to look like the following:

We would also try to address the balance of the car and the friction, both of which would have sped the car up by a slight amount. We would liked to have decreased the length of our car and used the bigger tires many other groups had taken.