Lego Racer

Prompt:
Build and design a vehicle with a single motor, powered by a PicoCricket, that can carry a 1.0 kg weight as fast as possible on a 4 meter course.

Engineering:
We began with learning about how torque and speed are inversely related: the faster the motor spins, the less torque it has which means the car won't be able to move when placed on the ground due to the insufficient amount of torque.  However, if we increase the torque but decrease the speed, it may mean that we will build a car that is too slow to win the race.  Friction was an additional factor that we had to take into consideration since it could also slow down our car.  Possible sources of friction included the wheels against the carpet and the number of gears meshing against each other.

Ultimately, the key to succeeding was to create the perfect gear reduction that would balance enough speed and torque that would move the car as quickly as possible without creating too much friction.  In order to create an optimal gear reduction by increasing torque and decreasing speed, the most logical decision was to use small gears to move larger gears.  This would cause the smaller gears to turn faster while the larger gears spun at a slower rate.  With this goal in mind, we set off to iterate several different gear reductions before we designed the car.

First Iteration:
After playing around with the gears to determine what meshed together better and observe what was physically possible, we decided that our baseline gear reduction would be the one provided in our packet.  This consisted of using three different pairs of 8-tooth gears to turn 24-tooth gears and yielded a gear reduction of 1:27.  We decided to add on the motor to see how it would work and made the newbie mistake of attaching the motor's 8-tooth gear to the gear train's 24-tooth gear.  This effectively reduced the gear reduction to 9:1 which produces an insufficient amount of torque.

We eventually figured it out

Second Iteration:
At this point we realized that using an 8-tooth gear to turn a 40-tooth gear provided the maximum amount of torque (1:5) and started to calculate a number of different ratios that would produce the most torque.  Modeling our design after our first iteration, we connected three pairs of 8-tooth gears with 40-tooth gears for a gear reduction of 1:125.   Getting this gear chain to run took an immense amount of power with just our hands but once we could get it to spin, the 8-tooth gear spun impressively fast while the 40-tooth gear spun extraordinarily slow.  Unfortunately we couldn't get this gear train to work reliably or at all but in the very least we were starting to build an understanding of what our gear reduction range was.

Calculated Iterations:

To make a smaller gear reduction and narrow our range down, we began to mix the combinations of gears.  At this point, we determined that it would be smarter to calculate the gear reductions first before building anything.  The following is a list of our varying calculations:

(8/40)(8/24)(8/40) = 1:75

(8/40)(8/40)(8/16) = 1:50

(16/8)(8/24)(8/40) = 2:15

(8/24)(8/40) = 1:15

(16/24)(8/40) = 2:15

(16/40)(8/40) = 2:25

(16/24)(8/24)(8/24)(8/24) = 2:81

We tested the first two and found that we couldn't get the gear train to move with the gear reduction of 1:75 but could move it from 1:50.  We then found that the 2:15 gear train lacked the torque to move and calculated a number of hypothetical situations thereafter to try to get it back within our range of 1:27 and 1:50.  Out of time, we quit for the day and sat on the ideas for a while.

Gear Worm Iteration:

It was at this point that I was partnered with Sam since both of our partners dropped from the class (they were both wonderful people).  Sam had been working on trying to get her worm gear to work.  We spent the majority of that class piecing together her worm gear with my previous gear train (8/24)(8/24)(8/40) = (1:45)

However, a number of problems began to occur.  For one, we couldn't get the gear reduction down because most of our time was consumed trying to get the structure holding the gears to work and gears to fit together.  Another problem was that the worm gear and connecting gear produced too much friction to the point where the gear was spinning at a much slower rate than it should.  After many frustrating attempts trying to get the structure of the car to allow the gears to mesh together and trying to reduce the friction between gears, we abandoned this design for my original and much simpler design.

Final Iteration:

We decided to go back to the very basics.  We were aware that using an 8-tooth gear with a 40-tooth gear provided the most efficient gear reduction.  We were also aware that 1:27 was our minimum baseline.  Therefore, we decided to use a pair of 8-tooth gears with 40-tooth gears to create a ratio of 1:25.  To set our car apart from others and reduce the amount of friction, we also decided to build a lightweight frame.

The result was a rather precarious car that ran backwards but also one that had the minimum amount of torque needed to move the car while maximizing speed and minimizing friction.  Our resulting time was 10.8 seconds which put us in first place for the class race.

Reflection and further iterations:

I have always known that rebuilding and testing was an inefficient method of trying to perfect a project.  However, I learn by observing so I could never fully grasp certain scientific concepts that required me to believe in the principles that they stated.  There is no doubt in my mind that they are correct; I just couldn't comprehend how it was possible because I was unable to observe it.  This is perhaps the first project I have encountered in which I relied more upon my calculations than sight.  I realized at some point that there was no way to distinguish between different gear ratios with my eyes which meant I had to trust that my calculations would reflect reality.  It seems like a simple logical line of thought but this project was just my epiphany into that world.

I think if I had been given more time, I would have tried to redesign the frame to be even lighter but sturdier.  Even though we tried to use the bare minimum amount of pieces to piece our car together, there are still some pieces that could have been redesigned and allow for a lighter car.  I would also be interested in trying to make an even slightly smaller gear reduction to try to see what is possible.