Modular Flexible PCB for Self-Reconfigurable Soft Robotics
Designed modular flexible PCBs enabling self-reconfiguring soft robotic modules to communicate and share power across an I2C bus and shared power rail. The project required integrating motor drivers, power regulation, and wireless connectivity onto a compact flex substrate with ENIG finish — then iterating through two full PCB revisions based on physical testing on the robotic platform.
Requirements & Constraints
Self-reconfigurable soft robots present a unique electronics challenge: the PCB must flex with the body, survive repeated mechanical deformation, connect reliably between modules, and support both motor actuation and inter-module communication — all within a highly constrained form factor dictated by the robot geometry.
The goal was to design a single modular PCB that could be replicated across every robotic module, enabling the full robot to self-reconfigure by sharing power and commands across a daisy-chained bus. Each module needed its own compute, motor control, and power regulation — communicating with its neighbors via a shared I2C line.
Key Constraints
- Support ESP32 wireless connectivity and computation in each module
- Drive two DC motors per module (bidirectional H-bridge control)
- Integrate a buck-boost power regulator (stable 3.3V from varying battery voltage)
- Enable module-to-module I2C communication and power sharing via connector interface
- Fit within the compact form factor of each soft robotic module body
- Use a flexible PCB substrate that survives repeated bending at flex zones
- ENIG surface finish for reliable solder joints and corrosion resistance on flex
- All SMD components — no through-hole components that would compromise flex zones
Design Approach
KiCad was used for schematic capture and PCB layout. All component CAD models were sourced from manufacturer libraries and imported into the layout. The design went through schematic review, DRC, and then fabrication with in-house SMD assembly and reflow.
Two Design Iterations
Revision A — Initial Design
The first revision implemented the complete electrical design on a flex substrate: motor drivers (DRV8837 H-bridge for bidirectional control), buck-boost power regulation (TPS63001 for stable 3.3V across varying battery voltages), and the ESP32-C3 module for wireless connectivity and I2C bus communication. KiCad schematics were captured with all inter-component connections, and the PCB layout was routed to fit the module form factor.
Revision A validated the core electrical design and communication protocols. Physical testing on the soft robotic platform revealed opportunities to improve component density, trace routing at flex zones, and the module-to-module connector interface reliability.
Revision B — Refined Design
The second revision incorporated feedback from physical testing. Layout adjustments improved routing at flex zones and tightened component placement. The modular connector interface was refined for more reliable module-to-module docking — a critical requirement for the self-reconfiguration use case where modules must reconnect in arbitrary orientations.
Key Component Decisions
- ESP32-C3: Compact wireless-capable microcontroller with I2C and UART support, fits on flex without rigid-flex compromise
- DRV8837: Small-footprint H-bridge motor driver for bidirectional DC motor control per module
- TPS63001: Buck-boost converter maintaining stable 3.3V rail regardless of battery state-of-charge
- ENIG finish: Gold over nickel for reliable solder joint formation and oxidation resistance on flex — critical for long-term reliability through repeated bending
- Castellated edges explored for module-to-module power and signal interconnects
Interactive Module Model
Physical Platform Validation
Both revisions were fabricated and assembled with SMD reflow soldering. The assembled modules were integrated into the physical soft robotic platform — a multi-module chain-like robot — and tested for functional connectivity, motor actuation, and inter-module I2C communication. Adjacent modules demonstrated reliable communication and shared-power operation under normal robotic motion.
Validation Results
- Module-to-module I2C communication functional across the full chain
- Motor actuation confirmed with bidirectional control on both drive channels per module
- TPS63001 regulation confirmed stable 3.3V under load across varying battery charge states
- PCB survived repeated mechanical flexing through normal robotic motion cycles
- ENIG solder joints maintained integrity through flex cycles during testing
Challenges & Lessons
- Flex zone routing required careful trace-width and bend-radius considerations to avoid trace cracking
- Module-to-module connector alignment was sensitive to manufacturing tolerances of the robot body; iterating on the connector footprint and approach was necessary
- SMD assembly on flex substrate demanded controlled preheat to prevent warping during reflow
Future Work
- Refine the mechanical docking interface for more reliable self-reconfiguration in arbitrary orientations
- Explore rigid-flex hybrid designs to improve reliability at high-stress connector regions
- Validate scalability of the I2C bus architecture with larger module arrays (bus capacitance limitations)
- Investigate castellated edge interconnects as an alternative to discrete connectors for cleaner module-to-module mating