System Level Design

Team Vision for System-Level Design Phase

In this phase, we planned to define the functions that our system has to perform and generate concept designs that will be able to perform these functions. Once we had concepts to compare, we planned to define the key metrics that were used to choose a concept to move forward with. After a concept was chosen, we planned to define the exact inputs and outputs that each of the subsystems will be needed to facilitate the beginning of our detail design. At the end of the system level design phase we planned to re-evaluate the risks that our project faces and adjust our plans accordingly.

We completed the following deliverables during this phase: Functional Decomposition, System Architecture, Benchmarking, Morphological Charts, Pugh Charts, System Level Designs, Risk Assessment, Engineering Analysis, Test Plan Outline, Updated Schedule

Functional Decomposition

Our Functional Decomposition encompasses all process we want our cart to fulfill.  As you move down our chart, you can ask the question "how?".  As you move from the bottom up the chart, you can ask the question "Why?".

Benchmarking

Purpose

Due to last year's team developing a comprehensive electrical system for the cart, our team focused on the mechanical subsystems and performed benchmarks for the collapsible, wheel, and power generation systems.

Collapsible System:

Solutions researched all had an emphasis on ease of collapsibility. The parameters that we decided were most important was the weight that the system could support and the achievable range of motion. 

Power Generation System:

Solutions researched were small scale power systems with an emphasis on portability including size and weight. The take away is that many commercial "small" systems still have large costs for low wattage gains.

Wheel System:

Solutions researched all had an emphasis on ease of movement. The parameters that we decided were most important was what materials the wheels could travel over and the overall cost. It should be noted that the "ease of use" row was filled out using our best guess. 

Battery Chemistry:

Solutions researched were rechargeable cells that are commonly used. Parameters that are very important is the cost per watt hour and the charge density. 

Criteria

Concept Development

Category	Function	Solutions
Education	Education	Display output on screen	Let user generate alt. power	Provide background reading to users	Provide video background to users	Have all parts visible to user	Provide demonstration to users	Bring cart to new users	Have cart send data to users by email	Regularly disconnect from grid to show functions	Have user build cart from scratch
Collapsibility	Handle	Telescoping	Folding	Sliding under	No handle	Retractable	Detachable	Latches to side	Spring loaded
	Body	Folding	Collapsing by handle	Metal snap collapsing	Crank lift and lower	Pneumatic/hydraulic system	Existing system	Scissor lift	Reverse 4-bar lift	Hand jack	Origami
	Generation components	Detachable	Foldable	Fixed in place	Rotate and store	Disassemble	Flexible	Modular	Stand alone
	Wheels	Foldable	Removable	Fixed in place	Bendable	No wheels
Electrical power systems	Battery physical size	Car	Motorcycle	Boat	Larger
	Battery chemistry	Lithium-ion	Lead-acid	Nickel-cadmium	Disposable	Capacitor	Molten salt	Pumped hydro
	Inverter	High wattage	Mid wattage	Low wattage
	Power output (outlets)	USB	Normal outlet	USB and normal	GFCI Outlet
Movement	Direction	Pull handle like wagon	Push handle	Handles on both ends	Bike attachment	Motorized push
	Ground contact	Motorized wheels	Slide cart on plastic bottom	Hovercraft technology	Lift with two users	Use rollers under cart	Put cart on rails	Pivot movement	Regular wheels	Multi-wheel	Tread
Energy generation	Solar mounting	Regular	Rollable	Modular	Tracking
	Solar technology	Mono-crystalline	Poly-crystalline	Thin-film
	Alt. 1	Pedal crank	Stair stepper	Wind power	Water turbine	Hand crank	Chargeable wheels	Hydrogen fuel	Concentrated solar
	Alt. 2	Pedal crank	Stair stepper	Wind power	Water turbine	Hand crank	Chargeable wheels	Hydrogen fuel	Concentrated solar

Feasibility: Prototyping, Analysis, Simulation

Trunk Space Sizing:

The purpose of this research was to ascertain more specific target numbers for trunk sizing that our solar cart should fit in to.

As a result of this research, we realized that our previous target trunk size (the Nissan leaf) was actually bigger than the average trunk size found in Colombia.  We now know that we cannot have two solar panels side by side, which was part of last years team's design. This affects how collapsible our cart needs to be.

Cart Extended Height & Table Top Sizing:

The purpose of this research was to get an idea as to how high our workspace should be and how much surface area the workspace should have. 

It is worth noting that the comfort level was based off of a man that is 5' 8.5" whereas the average size of an 18 year old from Colombia is 5' 6". Taking this into account, we see that an acceptable working range should be between ~27" and 36". This greatly affects our collapsing system and its design. As for the workspace area, a dimension of 23.5" x 48" seems to give ample room for the user to work while the space isn't too cramped.

Battery Life Simulation

The purpose of this research was to get a better idea as to how much energy our system will generate with just the solar panels and how much extra energy we would need under different working conditions.

Assuming an average load size of 120 watts and using the four solar panels that last years team bought, a spreadsheet was created to simulate how many days a year our system will fail under different conditions. The spreadsheet uses the geographic location of Cali, Colombia will a solar panel tilt size of 0 degrees. The spreadsheet uses component parameters from the battery and inverter that the last team bought. 

The spreadsheet allows the user to input start and stop times for when the user charges and uses the cart. The start and fail charge percentage for the battery can also be fixed. Of note, any fail percentage for the current lead acid battery that is below 80% will cause damage to the battery. Additionally, the user can also input parameters to simulate when the grid would fail. 

With this spreadsheet, we can better predict how much extra energy we need to generate with the two additional renewable energy sources. During the next stage, other potential renewable energy systems will be modeled and added to the spreadsheet. Then an optimization can be run to minimize cost while providing no system failures over the course of the year.

Battery Charge Simulation

Seamless Switching

This curve depicts the typical voltage interruptions that computing equipment can handle. Computing equipment is defined as technology that uses a switching power supply, which is analogous with the technology in a typical 3-d printer, therefore the curve is applicable to our project. As can be seen from the curve, the interruption from the time it takes to switch from grid power to inverter power should be no longer than 20ms.  

Morphological Chart and Concept Selection

We came to the conclusion that the best way for our cart to be collapsible is to use telescoping legs or a scissor lift leg system.  We used these ideas to come up with our different morphological charts.  

Rotating Solar / Scissor Lift:

This design encompasses rotating solar panels along with a scissor lift to raise/lower the cart.

Rotating Solar / Telescoping Lift:

This design encompasses rotating solar panels along with telescoping legs to raise/lower the cart.

Folding Solar / Scissor:

This design encompasses folding solar panels along with a scissor lift to raise/lower the cart.

Folding Solar / Telescoping Lift:

This design encompasses folding solar panels along with telescoping legs to raise/lower the cart.

Bicycle Powered:

This design has a bike that powers the cart, and also moves the cart from place to place.  It also has solar power.  

Concept Selection

Telescoping lift sizing analysis

Scissor lift sizing analysis

The telescoping and scissor height sizing analyses were used to justify the rating of size when collapsed and expanded height.

Pugh chart 1

For our first Pugh chart, when all of the designs were compared to the previous years cart design, the top design was our fourth design.

Pugh chart 2

When we made the fourth design the datum, none of the other designs scored better. The differences in most of the designs were in the categories that matched our key requirements for the house of quality. As a result of the second chart, we will most likely try to combine the third and fourth designs to try to use the strengths of both to create the best design possible. 

Designs and Flowcharts

The cart has 4 main sub-systems, each with their own input and output. When combined together, they form the functional basis for our cart.

• Folding System
• Movement System
• Electrical System
• Renewable Power system

Systems Architecture

Each sub-system has its own purpose in satisfying a specific need or requirement. 

Folding system : allows the cart to be portable and take up less space. This feature is critically important for travel in compact cars.

Customer requirements satisfied:

• • Easy to transport via car
  • Easy to transport via airplane
  • Collapsible

How will it achieve this?

• • foldable solar panels
  • modular system

Movement system: allows freedom of traversing. The cart will be used in a range of settings it must be able to navigate across. The energy generated from solar power greatly depends on location, cart must be able to navigate to position where power generation can be optimized.

Customer requirements satisfied:

• • Reliable
  • Mobile without vehicle

How will it achieve this?

• • optimal design
  • durable wheels

Electrical system: supplies power to the device. Can output educational information to the users. 

Customer requirements satisfied:

• • AC output
  • Can take unanticipated load
  • Switches seamlessly
  • Displays Power statistics

How will it achieve this?

• • taking power from multiple sources
  • monitoring status with sensors
  • communicating through peripherals

Renewable power system: harness power from multiple sources to charge the battery off the grid and educate users on renewable energy. 

Customer requirements satisfied:

• • Has two more sources than solar & grid power
  • Room for upgrades

How will it achieve this?

• • adding additional power sources

Risk Assessment

Design Review Materials

Include links to:

• Pre-read
• Phase Review Presentation
• Notes from review

Plans for next phase

In the next phase we will perform more feasibility work as our design becomes more detailed. After our concepts are confirmed or adjusted based on the feasibility information, we will begin creating drawings, schematics, and other supporting information for our design. While we are adding detail to our design, we will begin to fill out our bill of materials. As a result of our feasibility work, we will begin to develop test plans for the full-scale parts of our design as we develop the systems themselves. Finally, once the new information is generated, we will compare it to the work from the previous phases and make sure that our direction as a team is aligned with what our information shows.

Individual plans:

Garrett Waldron

Jacob Wildt

Christian Niebling

Matthew Madsen