3 Axis Center of Gravity Measurement Device

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Sponsors Schweitzer Engineering Laboratories
Team Name The C.O.G's
Duration 2018 - 2019
Faculty Adviser Dr. Michael Maughan
Mentor Matthew Harned
Client
  • Jonathan Richards
  • Sally Mei
Team Members
  • Kendall Gray
  • Kaleb Cartier
  • Eric Smead

The goal of the project is create a device that measures the center of gravity of Schweitzer Engineering Laboratories' (SEL) products. The device must be able to automatically measure the center of gravity in all three dimensions.

Problem Definition[edit]

Background[edit]

SEL designs and manufactures many digital products that provide protection to electrical systems around the globe. One such product is their protective generator relay. During shipping, because the relays are exposed to shaking and/or vibration, they can potentially sustain damage. Because of this, SEL performs vibration tests on the relays to determine if any components will be damaged. Determining the center of gravity can help them improve the products sustainability against this damage.

Deliverables[edit]

  • Proof of understanding of center of gravity measurement techniques
  • Decision matrix of brainstormed solutions
  • Proof of concept with at least a valid 1 axis measurement (Final prototype must be capable of measuring 3 axes)
  • Functional prototype, made using a variety of materials and methods
  • Validated measurements using an object with a known center of gravity
  • Plan for final prototype packaging OR repackage of another prototype
  • Record of total cost and steps for duplication
  • Final report containing full information listed above with detailed validation analysis

Specifications[edit]

  • Correctly measures each CG coordinate ±0.5% of that coordinate
  • Withstands a load of up to 50 lbs
  • Has a maximum size of 24" x 12" x 20"
  • Able to measure the CG of a product that is rack mounted
  • Operates while stationary
  • Stretch goal: Able to operate during a vibration test

Project Learning[edit]

Research[edit]

Four Load Transducers Method[edit]

Four Load Transducer device free body diagram (normal orientation)
Four Load Transducer device free body diagram (tilted orientation)

Article: "Measuring a Centre of Gravity of an Object Using 4 Load Transducer Method"

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Two Moment Transducers and Flexure Pivot Method[edit]

Top and Side Views of measuring device

Article: "Measuring Weight and All Three Axes of the Center of Gravity of a Rocket Motor Without Having to Re-Position the Motor"

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Measuring Table and Three Bipods Method[edit]

Measuring Table in normal orientation
Measuring Table in tilted orientation, measuring Z coordinate of CG of a frame

Article: "Mathematical Model Validation of a Center of Gravity Measuring Platform Using Experimental Tests and FEA"

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Preliminary Designs[edit]

Several preliminary designs were brainstormed in the early stages of the project, and while these designs were not fully implemented, the concepts of several were later implemented into the final design. The four preliminary designs that were decided against were the "Automatic Rotation", "Cantilever Beam", "Rack Mounted", and "Cantilever Beam with Box" designs.

Automatic Rotation[edit]

CG Measurement 2018 Preliminary Design 1 Image.png

In the Automatic Rotation design, three force sensors each are placed on multiple faces of the product. The measurement of the three CG coordinates uses the same principle and equations described in the Four Load Transducer article, i.e. summing moments about a datum in two different orientations. To find the CG coordinates in this design, the product would first be oriented with the sensors face down on a table. Using the force sensor readings, the X and Y coordinates of the CG can be found by summing moments about a datum. The product would then be rotated 90 degrees, and the Z coordinate can be found by once again summing moments. Since this method involves rotation, a mechanism that automatically rotates the product would need to be created to meet the requirement of minimizing user input.

While the Automatic Rotation design would meet the requirement of measuring all three CG coordinates, it is still flawed. Sensors required for every design take up the majority of the budget spending, so the design is cost inefficient due to the requirement of many sensors. It is also flawed in that the need for 90 degree rotation fails to meet the requirement for server rack mount capability. However, despite the Automatic Rotation not being the design of the final product, the concept of creating a mechanism that automatically rotates the measuring device was still implemented.


Cantilever Beam[edit]

CG Measurement 2018 Preliminary Design 2 Image.png

The Cantilever Beam design uses two force sensors and one torque sensor. The two force sensors are placed between the wall and cantilever beam, and the torque sensor is placed on top of the cantilever beam. The product that has its CG being measured is then placed on top of the cantilever beam which creates the reading on the force and torque sensors. It was hypothesized that this design would allow for the measurement of all three CG coordinates without having to reorient the device. If this were the case, the device would meet the requirements of minimizing user input, measuring all three coordinates, and rack mount capability.

However, after setting up the equations required to calculate CG coordinates, it was determined that all three coordinates could not be determined without tilting the beam to find the Z coordinate. After brainstorming ways to set this up, it was found that the Cantilever Beam design could not meet the rack mount design capability requirement if the device needed to be tilted. Thus, this design was decided against. However, the concept of using a cantilever beam was later implemented into part of the AT-AT prototype design.




Rack Mounted[edit]

CG Measurement 2018 Preliminary Design 3 Image.png

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Cantilever Beam with Box[edit]

CG Measurement 2018 Preliminary Design 4 Image.png

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Testing Prototype[edit]

Testing Prototype measuring CG of a milk carton
Testing Prototype in tilted position

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Prototypes[edit]

Prototype 1: "AT-AT"[edit]

AT-AT Prototype fully assembled

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AT-AT Prototype sensor and object positions













Prototype 2: "Star Destroyer"[edit]

Star Destroyer Prototype initial build

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Problems Encountered[edit]

3D Printing[edit]

Math Validation[edit]

Rack Mounted[edit]

Short Circuit[edit]

Melted Sensor[edit]

Design Considerations[edit]

Uncertainty Analysis[edit]

Strong Material[edit]

Accurate Sensors[edit]

Cost Effectiveness[edit]

Final Design[edit]

Validation[edit]

Team Members[edit]

Kendall Gray Profile Picture v2.JPG
Kendall Gray

Major: Mechanical Engineering
Hometown: Federal Way, WA
Graduation Date: May 2019
Future Goals: Job at The Boeing Company
Email: gray4747@vandals.uidaho.edu


Kaleb Cartier Profile Picture v2.JPG
Kaleb Cartier

Major: Electrical Engineering
Hometown: Athol, Idaho
Graduation Date: May 2019
Future Goals: Career as a control systems engineer for exoskeleton/prosthetic robotics
Email: cart5547@vandals.uidaho.edu


Capstone Eric Wikipage Profile Picture.JPG
Eric Smead

Major: Mechanical Engineering
Hometown: Saratoga, California
Graduation Date: May 2019
Future Goals: Career in machine design and/or fatigue analysis
Email: smea8590@vandals.uidaho.edu

Additional Documentation[edit]

Project Schedule

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Meeting Minutes

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Presentations

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Client Interview

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