For this assignment, Julia and I were given the challenge to create a car out of legos that would be able to carry a 1.0 kg weight across a 4 meter course as fast as possible. We were given a small grey motor that had high speed but low torque, due to its lack of internal gears, and a PicoCricket to power our car. Due to the motor’s low torque, we had to fashion our own gear chain that would increase the torque of the entire mechanism to be able to carry the weight the distance required, while also being as fast as possible.
Final design
When designing the gear chain, our first two iterations would keep on stalling and had a lot of unnecessary gears, something that also added to the complexity of our original structure. Our first gear ratio was 1/27, then 1/15. After our first two iterations, we stripped everything and started from scratch with a gear chain that had a gear ratio of 1/15, and it worked amazingly, with a time of 8s (speed of 0.5 m/s). Once we got the gear chain working, then we started to experiment with the structure of the car and how the weight would be carried, how the motor would be attached, and which wheels we should use. We tested the car with both the medium sized squishy wheels and the smaller, stiffer wheels, and decided that it would be more efficient if we used the medium sized wheels. We didn’t test out the larger wheels because we thought that having the car’s body farther above the ground would possibly affect the balance of the car, not only because the centre of gravity was higher up, but also because the wheels were thinner.
Iteration 1
Iteration 3
For the structure of the car, we wanted to keep it simple by making it a level- 4 wheel car. We designed the car so that the weight would be carried above the gear chain, with most of the weight spread evenly in the back of the car, with the PicoCricket sitting right in front of it. While we were designing the car, we were having difficulties in the placement of the motor and how to connect it to the gear chain, until we came up with the idea to switch all of the legos upside down and directly connect the motor board to the motor without the use of a wire so as to save space. We decided to have the driving force of the car to come from the back wheels.
If I had more time on this assignment, I would like to improve the structure of the car, possibly find a way to distribute the weight more efficiently. I would also like to test out the car with the largest possible wheels to see how much faster it becomes. Other than that, over all, I felt that Julia and I made a very efficient and well built car.
Your car was so compact! It was a really good idea to flip the entire thing upside down. My group ended up only flipping the motor’s mount upside down, and that was really clumsy.