3-Axis Center of Gravity Measurement Device

The goal of the project is to create a fixture for measuring the mass and center of gravity for standard Schweitzer Engineering Laboratories' (SEL) devices with complicated geometries and uneven weight distribution in all three dimensions.

=Problem Definition=

Background
SEL designs and manufactures many digital products ranging from transmission protection to control systems around the globe. To better understand the failure modes of the products, a series of mechanical analysis is performed by SEL. But Computer-Aided Design (CAD) models lack detailed information about component density, which leads to inaccurate measurement of the Center of Gravity (CG) of the product. By building a device, which measures the CG of the product automatically, using mass sensors will help to solve the issue of incorrect CG measurement of SEL products.

Deliverables
Proof of understanding of center of gravity measurement techniques Validation of functionality and robustness of the porototype using representative SEL components Proper documentation of the design ideas and measurements used in the project Record of bill of materials A detailed final reoprt of the project with a team presentation

Requirements
Calculates the center of gravity for complex objects in 3 dimensions​ Can measure objects approximately 20" cube down to the size of a cellphone​ Is completely automatic after the sample is inserted​ Displays a result within 3 seconds of measurement concluding​ Has an accuracy within 1% or 0.1 inches​ Hold a static load of 50 pounds​ Operate 1 year without maintenance​ Operate from a standard 120VAC outlet

=Project Learning=

Initial Design Ideas
This project was done by a capstone team in 2018-2019. So, at first, the ideas and works done by the previous team were studied. After brainstorming and research, two methods for the calculation of CG were decided by the team.

Compression method
The test platform is supported by three or more load cells, and the CG location is calculated from the difference in force measurement at these three points. Since the CG position is determined by small differences in weight measurement at these 3 points, huge CG errors can result from side loads using this method. In order to find the third component of CG, in the z-direction, the object being measured needs to be tilted to a known angle. When doing research on this method many academic papers and the handbook of measurements stated that it was important to tare the scales before placing the object on the test apparatus.

Prototype 1: Compression method


A square cardboard was used as the platform. A variety of solid objects with known CG such as aluminum cube and acrylic cylinder were used. Cheap amazon mass scales were used as load cells and the platform was glued to three nails and was on top of the scales.

Prototype 2: Tension method
A square plywood was attached to three luggage scales and the scale was attached to a table. Similar to compression method, different shape and size objects were placed on the platform to perform tests and obtain data points.

=Design Considerations=

=Final Design=

=Validation=

=Team Members=

=Additional Documentation=

Project Schedule



Meeting Minutes



Presentations



Client Interview