The Challenge:
Goodwill locations receive a significant number of donations after business hours. These items are often left outside, where they are vulnerable to theft, weather exposure, and impact damage. Existing donation bins and gravity chutes either prioritize security or accessibility, but not both — and none adequately protect fragile items.
The goal was to design a fully autonomous system that prevents unauthorized access, protects donated goods, and remains accessible and intuitive for public use.
We developed a two-door interlock architecture that physically separates the donor-facing door from the secured collection chamber. Only one door can open at a time, eliminating reach-in theft and enforcing one-way transfer.
My role:
This project was developed as a three-person engineering team. My primary contributions focused on mechanical system design, structural validation, and electro-mechanical integration.
I was responsible for mechanical system design and validation, including:
Full CAD assemblies in SolidWorks
Sliding door and frame design
Three-point locking configuration
Integration of a horizontal conveyor system
Electronics implementation
To validate the security architecture, I performed finite element analysis on the locking system under simulated forced-entry loading. The results informed final lock placement and structural reinforcement decisions.
The system operates through an embedded control architecture built around an Arduino-based controller.
Independent stepper motors actuate each door, while a servo-driven top lock enforces the interlock condition. Safety and sequencing rely on:
PIR sensor for human presence detection
Ultrasonic sensors for item verification
Limit switches for door position feedback
The control logic ensures the exterior door must fully close and human presence must be cleared before the interior door actuates and the conveyor transfers the item. After transfer, the system automatically resets and relocks.
CAD Design.pdfThe prototype integrates mechanical and electronic subsystems into a rigid enclosure fabricated from plywood, acrylic, and 3D-printed components.
Custom PLA parts were designed in SolidWorks for motor mounts, locking arms, and sliding rails. Mechanical alignment, motor synchronization, and lock engagement required iterative debugging and calibration to ensure smooth, repeatable operation.
The final system combines secure access control with controlled horizontal item transfer. Unlike traditional donation chutes, items are supported continuously on a level conveyor belt, eliminating vertical free fall and reducing impact damage.
The system was validated through repeated autonomous cycles and public usability testing. Over 30 users successfully completed the donation process without assistance, and the system demonstrated reliable interlock sequencing, safety lockout behavior, and jam-free operation.