Autonomous Delivery and Retrieval Rover

Overview

A three-person capstone project spanning two mission phases: a 4WD skid-steer rover that crosses varied terrain, descends a ramp, delivers a package into a tray, retrieves a second package, and returns — guided by four Time-of-Flight sensors and a 6-DOF IMU on an Arduino Due control stack.

Team Project & My Contribution

This was a three-person capstone project built across two development phases. Mechanical design — the chassis, gripper, and drivetrain mounts — was a team effort in CAD and DFM review. My work focused on electrical system integration, embedded software, and the control and sensor-related software running on the rover.

• Electrical system integration: wiring the Arduino Due, dual TB6612 H-bridge motor drivers, encoder motors, servos, four VL53L1X ToF sensors, and the 6-DOF IMU.
• Embedded software: the zone-based state machine (Navigate → Deliver → Navigate → Retrieve → Return) and its state re-entry and timeout-recovery logic.
• Sensor and control software: sequential I2C polling and median filtering across the four ToF sensors, IMU-based heading correction, and encoder-feedback control for wall-following and ramp traversal.

System Architecture

Software / Controls

The rover ran a hierarchical state machine across four zones — terrain navigation, ramp descent, maze delivery/retrieval, and return. Sequential I2C polling and median filtering stabilized the four ToF sensors on uneven terrain, while IMU feedback corrected heading after obstacle avoidance and during ramp climbs. State re-entry logic and timeout-based fallbacks were added after Phase B testing showed the rover could lose track of its position following a manual save-move.

Testing

• Staged testing in three steps: individual sensor/subsystem checks, obstacle-avoidance trials, then full-mission runs varying starting angle, lighting, and obstacle placement.
• Terrain navigation and obstacle avoidance performed consistently — the rover crossed the terrain zone without drifting.
• Ramp descent was stable and repeatable, confirming the IMU-assisted ramp-traversal logic carried over correctly from the previous phase.
• Drivetrain load testing showed stable electrical operation with no excessive heat or current draw; the theoretical torque margin for the 30° incline was not validated as a full climb during final testing.

Engineering Challenges

Failure Analysis

The final mission run did not complete the full delivery-and-retrieval sequence, and the causes were mechanical and navigational rather than software:

• Gripper: two hinge supports were missing from the arm assembly, so it lacked the rigidity to grip the package — a structural build gap, not a servo or control-logic fault.
• Terrain transition: the rover's wheels caught in the gap between the terrain section and an adjoining metal plate, requiring three manual save-moves to free it.
• State-machine desynchronization: those save-moves shifted the rover's position enough that its sensor readings no longer matched its expected state, and the state machine halted as a safety fallback before reaching the maze.
• What did work: sensor initialization, terrain-zone obstacle avoidance, and both ramp descents completed reliably, and FMEA had already flagged navigation, sensor initialization, and drivetrain activation as the highest-risk areas going in.