Garmin

Sonar Testing Structure (2022-2023)

Overview

In the classes EGR 101 and EGR 102 at Duke University, I led 2 teams of 6 total engineers each tasked by Garmin to create a structure that allows them to test the sonar capabilities of their diving watches and air tank sensors. The communication between these two devices allows one diver to see the status of a buddy’s air tank from their wrist.

Consistent and accurate testing of the communication between these two devices is essential to ensure that they make a product others are willing to trust.

The final design has been fully manufactured and delivered to the sonar test engineers at Garmin for product testing.

Background

The Garmin Sonar Engineering Team conducts their testing off of their pontoon boat in a local lake. However, their previous testing system lacked the stability required to generate reliable data. They previously used 3/4” diameter PVC poles, which we found during our test to deflect around 30” under a maximum load of 2kg. They also found that the PVC would deteriorate quickly when exposed to water and UV light.

1 | Stiffness

Less than 3" of deflection under max load of 18N

2 | Adjustability

An accurate rotational and depth adjustment mechanism for more advanced testing

3 | Durability

High UV and water resistance when exposed to the elements on the lake

Solution

The length of the arm is made from half-inch fiberglass rebar in a triangular configuration to increase the moment of inertia. We’re using fiberglass rebar because it is much lighter than traditional steel rebar while still maintaining similar strength properties. The length can be electronically adjusted from 9-16ft. One of the arms can also be rotated continuously.

All parts have been machined out of aluminum for superior durability and strength. The system is controlled using two, 131:1 gearbox motors receiving commands from an ESP32 on each arm and a web app on an engineer's laptop. Testing devices are to be fixed to the bottom of the system using a male 1/4"-20 thread.

Turning Mechanism

The turning mechanism can be continuously motor driven or set to turn intervals during testing.

The device uses a combination of waterjet cut aluminum machined aluminum, and machined delrin optimized for the smoothest turning possible.

Depth Adjustment

The depth adjustment mechanism can be set to specific depths or adjusted by increments during testing.

A spool controls the distance that the box tube at the bottom of the arm is able to telescope. The telescoping box tube gives a maximum extension of 7' past the initial 9'.

Hinge

The hinge mechanism allows the arm to be brought out of the water when the boat is underway and deployed at the testing site.

Each side is made from 1.25" thick aluminum cut using a solid wire EDM, a latch with a T-handle release located on the upper arm, and a rubber gasket.