Lego Racer J&M Take 2nd Place

Problem: Design a Lego car using the "old motor" (high speed, low torque) to move a 1 kg weight 4 meters across the finish line (and win the race!).

Partner: Marissa Okoli


First, we started by brainstorming possible variables that would affect the performance of our car:

1. speed-to-torque ratio
2. which size wheel to use
3. how many wheels to use
4. where the weight should sit in the car (front/back)
5. how the weight should sit in the car (standing up or lying down)
6. where should the motor me powering the wheels (from the front or back)
7. where to put the motor and the pico-cricket and still maintain a balanced car

Process: Mainly Composed of TONS of Trial and Error (fail fast and early, iterate as needed)

Trial 1:

After holding the 1kg weight in our hand, we thought we were gonna need a LOT of power, so we started with a huge gear ratio in an attempt to guarantee that we would be able to move the weight.

Gear Chain Ratio: 1/495

Conclusion: Way too slow, not so much power needed



Trial 2:

...Let's try something of the opposite extreme, a very very low gear ratio and just see if the car will move.

Gear Chain Ratio: 1/3

Reflecting now, I see that the big 40-toothed gear in the center was effectively useless, aside from the fact that it was adding friction. Regardless, I was learning about gear ratios.

Conclusion: Not nearly enough torque to move the weight.


Trial 3:

For the next iteration, I came and worked on a Saturday, so I assume that is what can be attributed to the major brain fartage here. As I was still new to working with gears, I added a lot of unnecessary gears. Although there are a ton of gears in this car, the gear ratio ended up being relatively low due to the way I arranged the gears.

Gear Chain Ratio: 1/45

Racing time: 24 seconds

Conclusion: At the time, I thought that the gear ratio here was 1/225, so we thought the gear ratio could still come down a bit. Other problems: the structure of the car is weak and the motor is not securely attached to the car. Also, needed to work on building a place for the weight to sit.

Other hilarious video of an attempt to test the car -- the weight was concentrated on the back, also where the wheels were being powered. The car was unbalanced and the weight was unsecured aka failure an an attempt to even move the car.


Trial 4:

Trying a lower gear ratio than (what we thought was) 1/225. At this point, I understand that trying these, in actuality, higher gear ratios is futile and not moving us towards the goal. Nevertheless, they were actual trials and part of the process of learning about how gear chains work.

Gear Chain Ratio: 1/125

Racing time: 40+ seconds

Iteration notes: lower the gear ratio even more (also, start keeping a more accurate chart of what you have tested and the times so you can problem solve a lot easier)


Trial 5: (wheel testing)

Short & Fat wheels: 50 seconds

Big & Skinny wheels: 32 seconds

It was at this point that we had decided that three wheels were what we needed for stability and weight distribution. Also the use of the large wheels, since they were directly hooked up to the gear chain turned at a 1-to-1 ratio with the final gear in the chain, so a larger wheel meant a greater circumference and a coverage of more ground with each turn of the wheel. #need4speed

Trial 6:   +Fail vid

Gear Ratio: 1/25

Racing time: 15 seconds

*gasp* It works at 1/25!! Now all we need to do is keep testing lower gear ratios until we have hit the lowest one that still moves the weight! The weight at the front of the car helps counter the 1kg weight.

Trial 7:

Gear Ratio: 1/15

Racing time: < 11 seconds

Iteration notes: After some online research, we found that laying the weight down flat would lower the center of gravity. In addition, we wanted to keep the weight centered and near the motor to optimize for speed.

Note: The car is a little bit lop-sided but with a bit of adjustment of the placement of the weight and the wheels, it is easily fixed.

Trial 8: How low can you go?

Gear Ratio: 1/10

Racing time: 13 seconds

Note: The 24-toothed gear was added in to have enough spacing to have the main axel and wheels fit together well, but at the cost of added friction.

Iteration notes: This gear ratio was so low that the car needed bit of a push to get started (overcome the static friction), but was able to make its way. However, we decided that this was not a better option than the clearly sufficient 1/15 gear ratio. Ladies and gentlemen, we have a wwwiiinnnneeerrrr! (hint: its not trial 8)

Trial 9: Final Product













Gear Ratio: 1/15

Racing time(on actual race day): 9.35 seconds

Note: the car tends to go to the left a bit, this was fixed just before the race through an adjustment in the wheel alignment

Reflection:

The process was long, but definitely worth-while in the end. This project was definitely different than the previous ones because all of the parts were pre-made, all we had to do was figure out how to fit them together in the best way. With each of the initial mistake I made in calculating the gear ratio, I quickly learned the correct way and made lots of progress towards a faster and better lego racer. I also learned how to set up a clear chart for keeping track of what we had tested and taking note of the numeric time that each lego racer took to cross the finish line (really a great idea for tracking progress and optimization). Overall, I spent about 15 hours on this project and I would not have spent the time much differently. Each iteration taught me valuable intuition and knowledge on the gear chain process and optimization. Now you tell me, which video did you like the most?

Skills/Motos:

• iterate, iterate, iterate
• fail fast and early
• keep meticulous notes (or videos) to help keep track and make progress with future iterations
• building strong/sturdy structures with legos
• adjusting gear chains
• working with bushings
• working with pico-cricket