My project for the underwater acoustics lab was a depth winch for vertical position control of a sonar transceiver, allowing for improved source positioning during acoustic tests. The winch is driven by two NEMA 23 stepper motors that have been coupled with 5:1 planetary gearboxes. The driving mechanism is a rack and pinion, with an 80/20 frame for structural stability and modularization. 

The central rack has a total length of 72", but 60" can be safely used. The vertical position and speed are controlled by the stepper motors by an Arduino and stepper motor drivers.

To the right, the full system is pictured, as well as a close view of the central drive train with the gearboxes, motors, and rollers.

To control the stepper motors to drive the winch, we developed the controller system shown on the left. It uses an Arduino UNO R3 board to run C++ code, and two DM332T stepper motor drivers powered by a 24V power supply. On the bottom left, the controller components are shown behind the winch, as well as the cantilever beam with a weight that allows for quick setup and takedown.

The code tracks the current position of the winch to ensure it does not travel out of bounds, and specific distances in inches can be input for accurate depth positioning. In Fall 2026, we plan to integrate the winch with a Blue Robotics BlueBoat, which would allow 3-DOF positioning of whatever hardware is attached to the winch for underwater tests.

To the right, the gearbox is pictured. The gearbox uses custom 3D printed parts and gears, as well as heat set inserts and various bearings to increase strength and improve torque transfer. We chose to 3D print parts since they meet strength requirements while allowing us to easily service the gearbox when things break. The planetary design provides a smaller footprint for a 5:1 ratio and aligns torques on 1 axis to simplify our assembly process.

On the far left, the pinion assembly is pictured. This proved to be one of the most intricate parts of the gearbox build, as the output shaft diameter was limited by the inner diameter of our largest bearing which was 12mm. The 1" pitch diameter nylon pinion was also a small amount of material to work with, which further constrained the design.

To the left, custom drilling jigs are shown. These allowed us to secure the pinion in a mill and drill holes exactly where they needed to be for both pinions to properly assemble with the steel coupler and output shaft. 

This assembly with 4-40 bolts, nuts, and a custom steel coupler is quite strong and easily transmits torque as needed from the gearbox output. We plan to improve the assembly in the future as currently it's quite intricate, but for immediate testing it has proven to be reliable.