Concept Design

To briefly introduce our system, we aim to create a power distribution system that safely and adequately powers our drone and its sub-components. Currently, we use an existing DJI distribution board. This board provides power to onboard electronic speed controllers (ESCs) and offers various XT60 and XT30 connectors in multiple types (male and female). While this setup works well for the original DJI Matrice 100 drone, it becomes insufficient when we plan to mount numerous custom components to support our missions, especially since these components operate at different voltages and currents.

Therefore, we need a new distribution system that continues to supply the drone with the necessary power for flight, maintaining compatibility with the original DJI setup. This means we must ensure sufficient power for the ESCs. Additionally, we need standardized connectors to provide power at 24V (10A) for some devices and 5V (2A) for others. Our system will continue using existing DJI batteries, as they offer a safer, more stable power source and compatibility with our current connectors. Besides our primary DJI battery input, we plan to add an auxiliary lithium-polymer battery to enable “hot-swapping.” This feature allows us to fully utilize the 20-minute time frame provided by the DARPA competition, rather than being limited to less than 15 minutes with our current batteries.

Updated Design Requirements: Since our initial design review, new requirements emerged based on feedback and updated subsystem needs:

• A radio requiring a separate 5V input, necessitating a new 5V line.
• An Ethernet splitter needing its own 5V input.
• An auxiliary battery dedicated to “hot-swapping” to maintain continuous power to the computer, avoiding shutdowns and restarts of critical systems.
• Current protection and regulation for the main system, addressing past incidents that caused significant component damage.
• An external power adapter we procured, removing the need for an onboard PCB voltage monitor.

How Our Schematic Meets These Requirements:

• On the main 24V line powering ESCs, we provide four DC barrel connectors directly powered by either the main or auxiliary batteries.
• The flight controller receives the correct 5V input through an XT30 connector, ensuring sufficient current and power.
• The Orin board connects to the 24V line via an XT60 connector, adjustable based on power requirements.
• The onboard radio (Rajant DX2) connects directly to the 24V line through an XT60 connector.
• The gimbal connects correctly via an XT60 connector.
• Two additional 5V lines, each supplying up to 2.5A, power the auxiliary radio and Ethernet splitter, sharing the network with the flight controller.
• Extra XT60 and XT30 splitters are included for the 24V and 5V lines, allowing additional components to be easily added or adjusted as needed.
• Two Schottky diodes ensure that the main battery’s voltage (24V to 22V) is always prioritized over the auxiliary battery. The auxiliary battery activates only when the main battery is depleted or disconnected.
• An LM2596 buck converter regulates voltage from 24V down to 5V, achieving 84% efficiency, surpassing our 20% efficiency target. This converter includes necessary capacitors and resistors for stable operation.
• Each power line includes a fuse to protect against current overload, adhering to maximum current limits.

Subsystem Calculations and Heat Management:

• The LM2596 buck converter subsystem, providing 5V output from a 24V input, achieves an efficiency of 84%. Under normal conditions at 2.5A, moderate heat generation is expected, raising the junction temperature about 27°C above ambient. However, during peak conditions (over 3A input), rapid heat buildup may occur. To handle this, a heatsink capable of dissipating heat through airflow is recommended, ensuring safe operation.
• The 1N5819-B diode subsystem can handle voltages up to 40V, operating safely between -65°C to +125°C. Its power dissipation decreases linearly from 1.25W at +25°C down to 0W at +125°C. Due to this specification, no additional cooling is necessary, although the diode will dissipate some power due to its forward voltage drop.

BOM