Gears of Greatness: A Lego Car (Part II)

We returned to the car during our next class period.  After much frustration last class, we were ready to make something work.  We knew that we should have the weight positioned as close to an axle as possible, and have short axles to increase structural integrity.  To maximize speed and sturdiness, we wanted a skinny, compact car made with the bare minimum of components.  We decided to not worry about the aesthetics or the particulars of the design so much, and just try to test out the gear train with the 1 kg weight on board.
Our first gear train (gear ratios 1:3 (pulley wheel) and 1:5 (tiny to large gear), so total gear ratio of 1:15):

We were very surprised when we first started the car without the 1 kg weight--the car reared up on its back wheels and shot forward.  Before completely scrapping this design, we decided to test once with the weight.

The first test:

Well, wow.  We didn't expect that to work.  Our car trundled along quite happily with the weight on board.

With the car finally moving (and moving very well, actually), we secured the gear train with a few more bushings and experimented with the chassis a bit. We kept the compact design, but slightly modified the weight platform to increase structural integrity (the first platform bent a bit) and minimize weight.

After we were happy with the chassis, we decided to test our car on the racetrack.  After about 4 trials, the mean time was 4.7 seconds for the meter race!  We felt pretty confident as the car whizzed along.

We weren't sure how to further optimize the design; after some brainstorming, we decided against changing the wheels (since they act similarly to a gear, and thus changing their diameter would change the gear train), but we tested various positions of the weight and changing the direction in which the car moved.
With the motor in the back, we first placed the weight at the very front of the car--this resulted in a mean time of 5.1 s/m (4 trials).  We then tried the weight in the middle--the mean time was 4.6 m/s.  Placing the weight in the back of the car proved much more difficult than expected--in 4/6 trials, the weight fell down and the car exploded when we tried to start the motor.  The car was even slower with the weight in the back.
Changing the direction of the car proved unhelpful; comparing the means of multiple trials, the car went slightly faster with the motor in the back than with the motor in the front (which makes sense, according to my knowledge of quadrupedal biology and how real cars work).
Our final design:

We finished our car early in the class period, so we were encouraged to experiment with other designs to find out what made ours work so well.  We tried a car with larger wheels and larger axles, which was very unstable and constantly exploded, causing much distress:

In the end, we raced our compact car to victory over a second faster than the next-fastest team.  Despite the initial struggles, eventually Project Lego Car was a resounding success!