Done in 21seconds

"Emma!" I shouted to my teammate at the other end of the track. Emma was about to place the hovercraft in the center of the track to start the run.

We were at the competition field for the Tech Challenge, "No Road, No Problem." (See my previous blog post for the rules) We just finished the two runs on the first track and the first run on the second track successfully.

"Edge!" I continued.

It suddenly dawned on Emma. She put the hovercraft against the edge of the track and released it. Instantly, the hovercraft raced down the track lined with sandpaper and carpet strips and crossed to the other end.

I quickly picked up our hovercraft, rushed to the next track, pressed it firmly against the edge again, and let go. The hovercraft shot across the pegboard sections and finished the 5th run on the 3rd track.

The stopwatch stopped at 21 seconds. We made a record in the competition.

Setting a record time wasn't just a matter of luck; it was about unique design, iterative improvements, careful planning, and playing smart. Here's how we made it happen:

1. Keep it simple and stay focused

At the beginning of the design phase, we decided to avoid using a fancy remote control to precisely control the hovercraft's direction, as the short length of the track would allow the hovercraft to cross it if the vehicle was traveling relatively straight and at a sufficient speed. This decision significantly simplified the project, allowing us to maintain our focus on optimizing speed and maintaining the hovercraft's direction.

2. Speed = Power + Propeller configuration - Weight

We implemented several strategies to enhance the hovercraft's speed:

• Reduce weight: We used lightweight materials for the hovercraft's body and optimized the overall design to strike a balance between performance and weight, e.g., reducing the number of propellers from two to one. Our final model only weighs 89g (without Payload), 118g (with Payload)

• Power Packs: We tested various battery combinations for the hovercraft's power pack, including AA vs. AAA, 1.5V vs. 3.7V, and Alkaline vs. Lithium. We settled on a solution that used a single 3.7V Lithium battery to power the propeller motor. It provided a powerful output in a compact volume and weight.

• Propeller Optimization: To determine the optimal propeller configuration, we compared the performance of various setups, including different propeller motor types (2-blade and 3-blade), single-motor versus dual-motor configurations, and airflow directions. Ultimately, we fixed our design with a single 3.7V 7mm x 20mm 65,000rpm drone motor and a 3-blade propeller that blows air backward.

• Motor Mount Design:

When optimizing the propeller configuration, we found that the shape of the motor mount (guard) played a significant role in the motor's efficiency. The tubular propeller mount in our final design not only provided a safeguard for the motor but also concentrated the blowing power, resulting in the strongest propulsion among all our other designs, including dual motor configurations.

All the optimizations led to consistent speed performance - the hovercraft was so fast that it reached the end of the track before it had time to change its direction.

3. Evolution of the hovercraft's shape - Solving the issue of getting stuck

Flat-head

Rounded Bumper

"Star Destroyer"

During testing, we encountered an issue where the hovercraft repeatedly stuck midway along the track against its sides, which led to a series of design modifications. The flat-headed shape of our early models was the primary cause of these stalls, as the hovercraft could not self-correct itself by either moving forward or turning back to the starting point. We added a rounded bumper, which significantly reduced this problem. The round bumper introduced slight instability to the stalls, which eventually triggered self-correction. Ultimately, the triangular ("star destroyer") design emerged as the most effective solution, especially when paired with an optimized propulsion system. The model's pointy and slim body made it very hard to get stuck. When hitting the side of the track, the hovercraft tended to slide along the edge and continue moving forward at least 80% of the time.

4. What doesn't kill you makes you stronger - Our Strategy

"What doesn't kill you makes you stronger" is one of my favorite lyrics. We found that the lyrics fit our case quite well - the edge of the track, which had given us so much trouble in the past, could be our key to success.

We discovered that when we placed the hovercraft against the edge of the track and then released it, the hovercraft could travel straight along the edge and cross the track every single time. Why? The thrust from the propeller, when slightly angled against the wall, broke down into two components: one perpendicular to the edge, which kept the vehicle pressed firmly against the edge, and one parallel to the edge, which pushed the hovercraft forward. The edge of the track became the guideline for the hovercraft to maintain its straight travel path.

Before the competition, we made this edge-release technique our core strategy. So when Emma seemed to forget and positioned the hovercraft in the center, I quickly reminded her with the word: "Edge!". That's the scene that happened at the beginning of the post.

I did not expect to write this much, but once I started, all the design choices, trial-and-error moments, and breakthroughs came flooding back. What seemed like small tweaks at the time — changing a propeller, adjusting a bumper, rethinking a strategy — were actually steps toward something bigger. The 21-second run was more than a record; it was a testament to creative problem-solving, determined persistence, and brilliant execution.