Team Vision for System-Level Design Phase (Nick)The goal for this phase was to come together as a team and make high level design decisions in order to give an overall "shape" to our final product. This phase is an important stepping stone between generating the customer and engineering requirements and figuring out the the specific real-world components that will comprehensively solve the problems defined in the problem definition phase.
Entering this phase our goals were originally to:
- Investigate battery technology
- Create FMEA documentation
- Create CAD mockups of remote system
- Select remote hardware
- Consult professors for wireless system and microcontroller selection
- Design system enclosure
- Obtain customer tricycle
- Create parameterized braking model
- Create CAD model of tricycle farme
- Create actuator mounting concepts
As we moved forward, the following was accomplished:
- Understand the conceptual functionality of SafeStop.
- Create a functional decomposition to map out the bridge between high level desired functionality and low level actuation.
- Create a conceptual, systems-level architecture diagram of SafeStop.
- Brainstorm methods of practical solutions for
providing desired functionality.
- Generate Morphological Charts for remote and braking system.
- Consider mechanical solutions for physical mounting and basic mechanical actuation.
- Create a list of metrics used to properly weigh
- Use the concept of Pugh matrices and chosen metrics to compare different design concepts.
- Make systems-level design choices, documented in the morphological chart.
- Generate CAD models of design choices where possible.
- Analyze the feasibility of bringing chosen system
into the real world.
- Use industry standards for basic metrics and testing methodology.
- Consider current draws, power requirements.
- Consider force and precision required.
- Consider required information density and data transfer throughput for wireless communications.
- Consider major components required to build the
- Benchmark different products to obtain rough estimate of cost, monetary or otherwise, versus performance.
- Use newly obtained design milestones to reassess project risks.
Revised Requirements (Justin)
Engineering Requirements (Metrics & Specifications)
Updated Risk Assessment (Eli)
- This figure demonstrates how the functionality of SafeStop transitions from a high-level system to low level actuation.
- At the top level implementation, the point of the
system is to remotely brake the recumbent tricycle.
- Going up answers the question "why?".
- Flowing down answers the question "how?".
Benchmarking (Gabe & Eli)
Concept Development and Morphological Chart
Concept Selection and Pugh ChartsThe following are the Pugh matrices created by the team for different aspects of the overall system.
- The datum is the chosen basis of comparison.
- P represents "plus", or an aspect better than the datum.
- N represents "negative", or an aspect worse than the datum.
- S represents "same", or an aspect equal to the datum.
General Design (Eli)
Feasibility: Prototyping, Analysis, Simulation
Financial Feasibility (Steven)
Actuator Feasibility (Steven)
Forces Acting Upon Brake Lever
Using the derived force, a potential actuator was found from Firgelli Automations.
Figurelli Actuator Range
Current Draws (actuator) (Nick)
When it comes to current draws, the overall braking system will exhibit similar power draws to the remote with the added load of an actuator. Based on the actuator benchmarks, a safe, relatively "worst-case" assumption would be a 12V actuator that draws 12A under maximum load. This would be a situation where the rider is pedaling at maximum force against the actuator's braking mechanism.
Two 6V RHINO lead-acid batteries with 13000 mAh capaticy in a series configuration would be able to fully power the actuator under constant full load for approximately 1 hour 5 minutes.
Four 3.6V Samsung Lithium Ion batteries with a 2500 mAh capacity in series configuration would be able to fully power the actuator under constant full load for approximately 12 minutes.
For a more realistic scenario, different very generous assumptions are made.
- Assume average braking events puts the actuator under full load for 10 seconds
- Assume an average of 12 remote braking events per hour
Under these assumptions, 10*12 = 120 total seconds of full load draw per hour.
- 120 seconds translates to 3.1% of the total 1 hour 5 minute capacity for the RHINO Lead-acid configuration, ~3% per hour, or ~33 hours of battery life.
- 120 seconds translates to 16% of the total 12 minute capacity for the Samsung Lithium-Ion configuration, ~16% per hour, or 6.25 hours of battery life.
Current Draws (remote) (Nick)
Information Density and Data Transfer Throughput (Nick)
- Assume upper end estimation of 5 bytes of information density required for comprehensive communication.
- Assumed 120Hz resolution for input recognition.
5 bytes * 8 bits per byte * 120Hz = 4800 bits/second of data throughput, or 4.8kb/s.
Wireless radios operating in the MHz range typically operate with throughputs in the megabit, or thousands of kilobits range.
Systems Architecture (Gabe)
Frame CAD (Steven)
Main Tricycle Frame
Remote CAD (Justin)
3D Prints of remote (Justin)
Plans for next phase
Team Gantt (Justin)
- Purchase test components
- Remote hardware & circuit design
- Battery selection & usage study
- Charging circuit design
- Facilitate prototype fabrication
- Wireless communication design & testing
- Brake force testing
- System mounting design
- Wireless communication design & testing
- Library creation