Science Olympiad Electric Vehicle

Second Design - Challenges and Solutions

One of the biggest challenges I’ve faced is powering a brushless motor with AA batteries, which isn’t exactly recommended. Brushless motors pull a lot more current than alkaline AAs are really designed to provide, and in most cases, you’d expect major voltage sag or the batteries just not being able to keep up. But, interestingly enough, my previous car, which actually had an even heavier load, ran just fine on AAs, so I know it’s possible. All of the battery holders on Amazon use thin wires (usually 22–24 AWG), which adds even more resistance and limits the current flow. To work around this if necessary, I am looking at building my own battery pack using 18 AWG wire, which would reduce resistance and deliver power more efficiently. If the setup has connection issues or proves unreliable, I would 3D print a custom battery holder to keep everything solid and secure and incorporate it in 18 AWG. Another option I considered was switching to brushed motors, which would be way easier on the batteries since they draw less peak current—the brushed motor that would apply enough speed requires 5 amps, only one amp less than the batteries would provide compared to the brushless motor which requires 12 amps—but I ultimately ruled that out for now because brushed motors are heavier and less efficient, which would hurt performance more than it helps.

As for the ESC issue, I know I talked about how many ESCs have built-in soft start features in their safety regulations, which was a problem since I need instant throttle response. The fix? Ditching the ESC altogether and using a simple motor driver instead. Unlike ESCs, motor drivers don’t have all the built-in safety regulations like soft start, power ramping, or current limiting, which means as soon as I send a signal, the motor gets whatever power I need at that moment with no delays.

Then there’s the braking system, which is another thing that needs to be carefully planned. I’m going with a wing nut braking system, meaning I need a threaded rod for the braking mechanism and a non-threaded rod for the main drivetrain. This setup ensures the braking system is independent of the drive system, which is a huge benefit in terms of control and reliability. I also considered whether it would be worth achieving all-wheel braking using a timing belt and two timing pulleys, but that would add weight and make the design way more complicated, especially when it comes to figuring out how the gears would attach to the front axle. For now, that extra complexity just doesn’t seem worth it.

Another challenge was finding a way to allow the 6mm threaded rod to spin freely with minimal friction while maintaining a compact and lightweight design. The issue arose when I realized that standard 6mm ID ball bearings were not designed for threaded rods, as the threads would create unwanted friction and wear. I explored several potential solutions to address this problem. One option was to use a 6mm to 10mm sleeve adapter, which would fit over the threaded rod and create a smooth surface for the bearing. However, finding an off-the-shelf sleeve with the exact dimensions proved difficult, and custom machining a perfect fit would add unnecessary complexity. I eventually ran with the solution by finding an M6 threaded coupling nut as an adapter. This nut naturally fits onto the 6mm threaded rod, and if its outer diameter is close to 10mm, it will act as if it were a non-threaded rod rotating inside the 10mm flanged bearing. To optimize this setup, I considered minor modifications such as sanding the nut down slightly for a better fit, lubricating it to reduce friction, or even securing it inside the bearing with Loctite. This approach eliminated the need for complex adapters while ensuring a low-friction, stable rotation system.