The Physics of Failure: Why Standard Li-Ion Collapses at -25°C

In the world of small unmanned aerial systems (sUAS), the datasheet usually lies. A platform rated for "40 minutes of endurance" in California will often fail within 8 minutes in the Canadian High North.

The culprit is rarely the airframe or the motors. It is the chemistry inside the battery cells.

At Northstrike, we do not view cold weather as an edge case. We view it as the baseline operating environment. This brief outlines the physics of the "Cold Start" problem and the active thermal architecture required to solve it.

The Chemistry of Voltage Sag

Standard Lithium-Ion (Li-Ion) and Lithium-Polymer (LiPo) batteries rely on the movement of lithium ions between the cathode and anode through a liquid electrolyte.

As ambient temperature drops below 0°C, the viscosity of that electrolyte increases. This physical thickening makes it harder for ions to move, drastically increasing the cell's Internal Resistance (IR).

When a flight controller demands a surge of current (e.g., during takeoff or a high-speed maneuver), that high internal resistance causes an immediate drop in voltage. This phenomenon is known as Voltage Sag.

The result:
The battery might chemically hold 80% capacity, but the voltage sags below the flight controller’s safety cutoff (usually 3.2V or 3.0V per cell). The drone detects a "Critical Battery" event and initiates a forced landing—or worse, the ESCs lose synchronization and the aircraft falls out of the sky.

The Passive Failure: Why Insulation Isn't Enough

Most manufacturers attempt to solve this with passive insulation (foam stickers) or by telling operators to keep batteries inside their jackets until deployment.

This is a failure of design.

1. Wind Chill & Prop Wash: A drone moving at 60km/h creates massive convective cooling. Passive foam cannot retain heat against that level of thermal stripping.

2. Cold Soaking: If a drone sits on the tarmac for 15 minutes waiting for a mission command, the core temperature equalizes with the ambient air. By the time the rotors spin, the chemistry is already compromised.

The Northstrike Solution: Active Thermal Management

The Scout Mk.1 architecture treats the battery cartridge not as a fuel tank, but as a life-support system. We utilize a bi-directional Active Thermal Management System to maintain cell chemistry within the optimal

20∘C−25∘C20∘C−25∘C

window, regardless of outside temperature.

1. Pre-Flight Conditioning
Upon system boot, the onboard power management unit (PMU) checks the core temperature of the battery pack. If it is below the threshold, the system engages resistive heating elements integrated directly into the battery housing. This pre-conditions the electrolyte before the motors ever spin.

2. Waste Heat Circulation
During flight, the onboard compute (SBC) and avionics generate significant thermal energy. Rather than venting this heat into the atmosphere, the Scout’s internal airflow topology routes this waste heat over the battery cartridge, creating a thermal buffer against the arctic air.

Material Resilience: Beyond the Battery

Energy is only half the equation. Structural materials also change properties in the cold. Standard ABS and PLA plastics become brittle and shatter under impact at -20°C.

The Scout airframe is printed using Annealed PA12-CF (Carbon Fiber Reinforced Nylon). We utilize a specific annealing process that aligns the polymer chains, ensuring the chassis retains ductility and impact resistance even in deep freeze conditions.

Conclusion

Reliability is not about surviving the best day; it’s about surviving the worst. By engineering for the thermal realities of the Canadian Arctic, we ensure the Scout platform delivers consistent, predictable endurance when other systems remain grounded.