15 January 2024

The landscape of FPV drones has been witnessing a gradual increase in battery cell count, with each progression bringing its own set of advantages and challenges. In 2015, 4S surpassed 3S as the standard, and by 2018, the enthusiast community was captivated by the allure of 6S. Fast forward to 2023, and the spotlight is now on an even higher voltage - the 8S. If you've been curious about the reasons behind this shift, you're certainly not alone. In this article, we'll delve into the motivations behind the 8S trend, examining both the merits and drawbacks of utilizing 8S batteries. The aim is to assist you in determining whether constructing an 8S drone in 2023 is a viable idea.

When we talk about 8S, we're referring to the number of cells in a LiPo battery, which ultimately dictates the battery voltage. So, what does it take to fly an 8S drone?

Battery: If you're ready to make the leap to 8S, you can acquire 8S LiPo batteries from this source: Link.

Charger: It's crucial to note that most LiPo chargers available on the market support up to 6S, making an investment in an 8S-compatible charger a necessity.

Motors: Selecting motors with an appropriate KV is essential. Generally, a KV range of 1200 to 1600 works well for 8S, comparable to 1600-2100KV on 6S. If you have 6S motors compatible with 8S voltage, they can still be utilized by setting a 75% output limit in Betaflight, similar to flying 6S on 4S motors.

FC and ESC: An 8S-compatible FC/ESC stack is a must. Currently, options are limited, with the Foxeer stack being the only one I'm aware of.

Advantages of Higher Voltages: Leveraging higher voltage for FPV drones comes with several advantages. This is evident in the shift from 4S to 6S, where a higher voltage can deliver the same power at a lower current, resulting in less heating across various components. Reduced current also helps mitigate battery voltage sag, enhancing throttle control, responsiveness, and maintaining consistent performance throughout the entire flight.

Transitioning from 6S to 8S offers similar benefits, such as reduced voltage sag and increased efficiency due to lower system losses. However, as voltage continues to climb, the returns begin to diminish. It's crucial to weigh these advantages against the potential drawbacks of higher voltage.

The Issue with Higher Voltages: As explained in my motor buyer's guide, Motor KV represents the motor's speed measured in RPM per volt applied. Achieving the same RPM requires lower KV motors with higher cell count batteries, potentially leading to worse cooling performance. While the rise in motor stator windings when switching to 8S might not pose a significant cooling issue compared to 6S, higher voltages like 12S or 16S could present cooling challenges that require further testing.

Currently, 8S batteries are relatively rare, and if found, they tend to be more expensive and bulkier than their 6S counterparts. Few FPV drone components can handle the higher voltage of 8S, potentially necessitating a voltage regulator for electronics. Most components are designed for 6S, and insufficient testing for 8S compatibility may increase the risk of failure.

When using 8S, close monitoring of voltage is crucial, as performance doesn't degrade significantly even at low voltage. Overlooking this could lead to overdischarging the battery, risking a sudden drone drop without substantial warning.

Conclusion: While the allure of building an 8S quad is tempting, my current advice would be to exercise caution.

Firstly, it's likely to be a costly endeavor, requiring investments in new 8S batteries, compatible chargers, and limited options for motors and ESCs. Durability can be a concern, given that most components are only tested for 6S, and comprehensive testing for 8S is yet to be conducted.

Secondly, the potential for damaging an 8S LiPo battery is higher due to the larger number of cells.

In summary, while 8S has the potential to enhance flight performance, it comes with significant challenges, including higher costs and a lack of reliable hardware options. Whether to switch ultimately depends on personal needs and flying style, and as more manufacturers delve into the development of 8S-compatible components, it might become a more feasible choice in the future. Always let your individual requirements and flying preferences guide your decision-making process.