🔋 Battery System

Initial Setup

At the beginning of the project, the robot was powered using a 24V 20Ah commercial Li-Ion battery.
While this battery met our power requirements, it proved impractical for transportation during competitions due to its size, weight, and airline restrictions.

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Redesign in 2025

In 2025, we decided to design and build our own custom battery pack. This decision was driven by:

• The robot not requiring the full 20Ah capacity;
• The need for a lighter, more compact, and travel-friendly power solution.

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Power Consumption Analysis

To determine the proper battery size, we powered the robot using a lab power supply and measured the real-time current draw during regular operation. A graph was then created to visualize the average and peak current consumption.

From the data, we observed:

• Average current draw: ~1.0A
• Peak current draw: ~1.7A

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Cell Selection

After analyzing the power requirements, we chose Samsung 18650 LiFePO4 cells.
The decision was based on:

• Availability and affordability;
• Recommendation from a university professor;
• The reliability and safety of LiFePO4 chemistry.

Each cell provides:

• Nominal voltage: 3.7V
• Nominal capacity: 2.2Ah
• Maximum capacity: ~4.4Ah

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Battery Pack Configuration

To meet the robot's 24V requirement, we calculated the number of cells needed in series:

To meet the 24V requirement:

24V / 3.7V ≈ 6.5 → 6 cells in series

As each cell could handle the required current, no parallel connections were necessary.
The final configuration was:

• 6S1P (6 cells in Series, 1 in Parallel)

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Assembly Process

Once the cells arrived, we proceeded with the assembly using spot welding and nickel strips to connect the terminals.

To protect the battery and increase its reliability, we added a Battery Management System (BMS).
Additionally, we designed and 3D printed a custom case to prevent short circuits and ensure safe handling.

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Test Results and Deployment

In our tests, the battery voltage dropped from 25.2V to 22V after one hour of continuous operation, proving that a single battery was sufficient for standard task duration.

To ensure uninterrupted use during competitions, we built two identical battery packs.
This way, one battery can power the robot while the other is recharging.

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Summary

Parameter	Value
Voltage	24V (6 × 3.7V)
Capacity	2.2Ah nominal, 4.4Ah max
Chemistry	LiFePO4
Configuration	6S1P
Average current	1.0A
Peak current	1.7A
Discharge Test	~25.2V to 22V in 1 hour
Battery Packs	2 (1 in use, 1 charging)

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💡 Future improvements may include a smarter BMS with telemetry, or integrated power monitoring for logging battery usage during matches.