Lego Car

For this project we were required to build a vehicle out of legos that could move sustaining a 1kg weight with a single PicoCricket motor. We were then required to race our car across a 4 meter track to see whose was the fastest.

Torque vs. Speed and Gear Trains

We first experimented with the relationship between torque and speed. We knew that the two have an inverse correlation, but we wanted to see how that applied to actual Legos. To do so we made a small gear train where the driver was an 8-tooth gear. We then added on some 40-tooth gears and ended with a 16-tooth gear as our follower. You can see the varying speeds of each gear as it runs on a motor.

The Motor and First Iteration

Because the motor we were using had a large speed and a small torque, we knew that we needed to somehow increase the torque enough so that the car could move with the weight. However, we did not want to to make our car too slow so that it wouldn't win the race. Because of this we started our first model with only two gears, going from small to large in order to increase the torque. We also knew that less gears meant less friction, which is good to maintain the speed.

Second Iteration

Sadly, two gears were not nearly enough to support the weight we needed to carry, and our car was larger than it needed to be, adding unnecessary weight and slowing it down. Additionally, the front wheel did not need to be so large because it was not attached to any gear. We decided that it would be best to implement a small gear train to increase the torque. Several different arrangements of gears were tried, one pictured below:

However, the optimal gear ratio we found used only 16-tooth and 40-tooth gears.

Final Iteration
Our final gear ratio ended up being 16:40 16:40 16:40= 8:125= 1:15.625. We also made our car much smaller and narrower to increase speed and exchanged the front wheel for a smaller one. We used shorter axels running horizontally so that we we're able to push the wheels closer to the car. This way, the friction on the axels would be reduced because the weight put on it was closer to the center. This made the gears easier to turn.

Time

Between our many trials, we clocked 8.7 to 9.7 seconds for the 4 meter course. We noticed however that our car ran ever so slightly to the left when it was turned on, so to remedy this we shifted the battery over to the right side of the car hoping that would create balance. However, when we did this we noticed that our time was reduced by several seconds. So we decided finally to choose the lesser of two evils and replace the battery in the center. Our final time was officially 9.63 seconds, coming in as one of the top 3 fastest cars in the race.