Introduction:
In the ever-evolving world of FPV drones, battery cell count has played a significant role in shaping the performance and capabilities of these flying machines. Over the years, we have witnessed the shift from 3S to 4S as the standard in 2015 and the rise of 6S as the preferred choice by 2018. Now, as we enter 2023, a new trend is emerging, and it revolves around an even higher voltage option - 8S. In this article, we will delve into the reasons behind the growing popularity of 8S batteries, explore the advantages and disadvantages they offer, and help you decide whether building an 8S drone in 2023 is a viable choice.
Understanding 8S:
When we talk about 8S in the context of FPV drones, we are referring to the number of cells in a LiPo battery, which determines the battery voltage. It's essential to have a basic understanding of battery fundamentals and the various cell counts available. If you need a refresher, you can refer to my comprehensive LiPo battery tutorial for more information.
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What Do You Need To Fly 8S?
If you are ready to embrace the world of 8S drones, there are specific components and equipment you will need to ensure a successful build. Procuring 8S LiPo batteries is the first step, and you can find them from various sources. However, it's worth noting that most LiPo chargers on the market only support up to 6S, so investing in an 8S-compatible charger becomes a necessity.
In addition to batteries, you will require motors with an appropriate KV rating for 8S operation. Generally, a motor with a KV range of 1200 to 1500 works well for 8S, which is comparable to 1600-2000KV motors on 6S. If you already have 6S motors that can handle the increased voltage of 8S, you can still use them by limiting the output to 75% in Betaflight, similar to how people fly 6S on 4S motors.
Furthermore, it is crucial to have an 8S-compatible flight controller (FC) and electronic speed controller (ESC) stack. However, it's worth noting that the options for 8S-compatible FC/ESC stacks are currently limited. If you are aware of any available stacks that support 8S voltage, sharing that information in the comments section would be greatly appreciated.
Advantages of Higher Voltages:
Using higher voltage to power FPV drones offers several advantages, which explains the transition from 4S to 6S as the preferred choice for 5" FPV drones. In a previous article, I discussed the benefits of moving from 4S to 6S in detail. The main takeaway from that discussion is that higher voltage allows for the delivery of the same amount of power at a lower current. This translates to reduced heating across the entire system, including the battery, connectors, wires, ESCs, and motors. Lower current also mitigates battery voltage sag, resulting in improved throttle control, increased responsiveness, and consistent performance throughout the entire flight.
Switching from 6S to 8S brings many of these same advantages, such as further reduction in voltage sag and increased efficiency due to reduced system losses. The higher voltage allows for more power to be delivered without pushing the current to its limits, resulting in cooler and more efficient operation. However, it's important to note that as the voltage continues to increase, the returns in terms of performance gains start to diminish. This means that the benefits of 8S need to be carefully weighed against the potential drawbacks, which we will explore next.
The Issue with Higher Voltages:
While higher voltages offer significant advantages, they also come with potential challenges that need to be considered. One of the key considerations when using higher cell count batteries is the requirement for motors with lower KV ratings to achieve the desired RPM. Lower KV motors are achieved by increasing the number of wire turns around the motor stator. However, this increase in stator windings can potentially impact cooling performance. When switching to 8S, the rise in motor stator windings might not pose a significant cooling issue compared to 6S, and any potential cooling concerns are likely to be offset by the lower current draw and increased efficiency gains. However, it's important to note that further testing is needed for even higher voltages like 12S or 16S, as cooling could become a more significant issue.
Currently, 8S LiPo batteries are relatively rare compared to their 6S counterparts, and if you do find them, they tend to be more expensive. Additionally, 8S batteries are generally bulkier, adding weight to the drone. This increased weight raises the likelihood of battery ejection and damage during crashes, impacting overall durability.
Furthermore, the availability of FPV drone components that can handle the higher voltage of 8S is limited. Most components, including flight controllers and video transmitters, are designed with 6S in mind and have not undergone sufficient testing for 8S compatibility. This compatibility issue could potentially increase the risk of component failure when operating on 8S voltage. In some cases, a voltage regulator may be required to power your electronics if they are not directly compatible with 8S.
When using 8S batteries, it becomes crucial to closely monitor voltage levels. Due to the nature of higher cell count batteries, the performance degradation at lower voltages is not as significant as with lower cell count batteries. This means it's easier to overlook and unintentionally overdischarge the battery, which can lead to a sudden drop in performance or even a complete drone failure without sufficient warning.
Conclusion: Not Recommended in 2023
While the allure of building an 8S quadcopter is strong, it is important to consider the current state of the technology and the potential challenges it presents. At this point in time, my personal recommendation would be to hold off on building an 8S drone in 2023.
First and foremost, building an 8S drone can be a costly endeavor. You will need to invest in new 8S batteries and compatible chargers, which may already be pricier and harder to find compared to 6S alternatives. Furthermore, the options for motors and ESCs that support 8S are limited, and durability concerns may arise due to the lack of extensive testing on 8S-compatible components.
Additionally, the risk of damaging an 8S LiPo battery is higher due to the larger number of cells. Mishandling or improper use of 8S batteries can lead to significant damage, both to the battery itself and the drone.
While 8S has the potential to outperform 6S in terms of flight performance on paper, it is essential to consider the overall ecosystem's readiness. The lack of reliable hardware options, compatibility issues, higher costs, and potential durability concerns make it a less feasible choice in 2023. Over time, as more manufacturers delve into the development and testing of 8S-compatible components, the landscape may change, and 8S could become a more viable option. As always, your personal needs, flying style, and risk tolerance should guide your decision-making process when considering a switch to 8S.