Team Vision for Detailed Design Phase
The Detailed Design phase is a culmination of the work that has been completed over the course of MSD I. We now have finalized detailed designs for each subsystem, and a modeled design of the entire system. The team has performed several feasibility activities, including calculations and prototyping, to ensure that our designs will act as intended. Additionally, we have developed a Bill of Materials off of our designs which we will use to purchase the materials necessary to build our product. Our test plans have been written for future use, in both subsystem and user testing. Finally, our current risks and plans for the future have been documented, and will be used to guide decisions and actions in the future.
Prototyping, Engineering Analysis, SimulationIn phase 4, we constructed the next iteration of the launch assembly prototype as well as prototyped the indicator circuit. In we started conducting preliminary prototyping on the frame material and geometries. In addition, for the frame to be able to fit the majority of wheelchairs the various telescoping aspects require a range to determine the limit it can be extended and condensed to.
Drawings, Schematics, Flow Charts, Simulations
Timing Diagram of Overcomer Lower Extremity Use
Circuit Schematic of the Beacon System
Catch and Launch Renderings
The catch and launch subsystem begins with the formation of the base. Our CAD model mimics our choice of PVC tube and PVC fitings for the base. It can also be seen that casters will be attached the bottom, sides of the base. The curved piece will also be made out of PVC and acts as bumper to catch the and locate the ball in.
The passive catching mechanism sub assembly is then built onto the base. This includes bent catching arms that rotating on sholder bolts that act as a pin. Shoulder bolts are also attached to the tops front corners of the base to act as a place for our passive catching springs to attach to. Our catching springs attach from these bolts to small screws drilled into the PVC catching arms.
Next, our launching sub assembly, seen below, is attached onto the current assembly. This starts with a shoulder bolt to act as a pin at the back corner of the base. A spaced is slide on the pin, followed by the launching base arm. The base arm is hollowed out in the center to allow this to be attached adjustably along the length of the bar.
A plunger, seen on the left, that will strike the ball is attached to the bar and will be place so that it will strike the ball in the center. On the right below, is the connection to the user interface and energy generation. A cable will be attached the end of a carabiner. The carabiner can be attached and unattached at anytime to the eyebolt, permanently fastened into the launcher base bar.
The full system is shown below. A screw is fastened into the end of the launching base for one end of the launching spring to be attached to. The other end is attached to one of the shoulder bolts at the front end of the PVC base. It can be seen in the picture on the right, that heights of the catching, launching and spring materials were carefully constructed so that the arms connected to the plunger will strike the screws in the PVC catching arms. However, the heights leaves this as the only contact allowed, which should reduce the risk of parts breaking.
As described, the launcher will be connected a cable that connects up to the user. The user will then crank the user interface to retract the cable and pull the launcher back. This can be seen in the image below to the left. Then the user will release the cable and the launching spring will send the launcher back out to strike the ball and arms. This can be seen by the picture on the right.
User Interface Renderings
Function Cue and Sensor Renderings
We additionally modeled up in SolidWorks some of the sensors that we plan to watch. Below on the left we have our catching sensor. The sensor can tell when material is inbetween its arms. We will 3D print the disk shown in blue and will fix it to rotate with our arms. Based on the design and proper assembly of the disk, the sensor will be able to tell when the arms have rotate inwards towards the wheel chair and have caught the ball.
Below on the right we have our launching sensor. When the launcher is moves backward to be loaded and when moves forward in launch the button on the sensor will be tricked on and off. Both sensor will connect to a light on the user interface that indicates the information discussed above.
Integration of Subsystems
For the assembly of the subsystems to really be helpful in visualizing our product we needed it assemble it in reference to a wheelchair. We obtained CAD files of both an electric and manual wheel chair. The parts can be seen below.
As the electric wheel chair was our target group, the Overcomer subsystems were assembled on the electric wheel chair. The subsystems were assembled according to how we thought they were truly assemble in real life.
Engineering DrawingsFor the repeatability of our work by others, we must produce engineering drawings of parts that we will be fabricating or modifying. These essentially are instructions, depicting the location and dimensions of any machine work necessary.
Description of Engineering Drawings Necessary
|BOM Item Number||BOM Item Name||Number of Total Drawings||Drawings for:||Notes|
|1||Larger Telescoping Tubes||1||Fabrication||Drawings mainly for dimensions and radius of bends and drilled holes|
|2||Smaller Telescoping Tubes||1||Fabrication||Drawings mainly for dimensions and radius of bends and drilled holes|
|11||PVC Tubes||5||Modifications||Drawings mainly for location and diameter of drilled holes, cuts to separate catching arm tubes from each tube of base, drawings of bends for arms and bumper|
|12||PVC Fittings||1||Modifications||Drawings mainly for location and diameter of drilled holes|
|30||Aluminum Flat Bar||3||Fabrication||Drawings for launcher base (dimensions, cutout, hole and thread), plunger arms (dimensions, holes and threads) and launching sensor bar (dimensions and hole)|
|38||PVC for User Lever||1||Modifications||Drawings for small modifications for attachment|
|39||Upper Casing||1||Fabrication||Drawings for design of 3D printed part|
|40||Lower Casing||1||Fabrication||Drawings for design of 3D printed part|
|41||CAM||1||Fabrication||Drawings of dimensions for machine work|
|43||Disk for Catching Sensor||1||Fabrication||Drawings for design of 3D printed part|
Bill of Material (BOM)During this phase, we started to narrow down on material choices and developed a bill of materials. Our live BOM can be found on Google Sheets and includes the costs of purchasing for our project and also an estimate of the manufacturing cost of each part.
While we sourced every part on our BOM to ensure repeatability for anyone that tries to replicate our process, many of the parts listed will be able to be obtained for free around campus. These parts are often scrap or surplus material that is available for RIT students.
Considering this, our maximum cost assuming no parts can be obtained for free is $424.97. Our minimum costs, assuming we can obtained the materials we specified for free, is $183.50. One consideration to this, is the cost of 3D printed material which has not yet been calculated.
Based on catalog cost to manufacturing cost ratios we learned from other product development classes, we were able to estimate the manufacturing unit cost for the current design of our product. The manufacturing cost is $148.39.
The largest costs associated with our project were:
- Frame Tubing ~$150. We are estimating this cost based on the length of tubing that we need and material choice of 1018 and 4130 Steel. This material will not be able to be obtained from surplus.
- Bumpers: ~$65. The bumpers on the bill of materials were from McMaster Carr, a generally expensive vendor. We found these McMaster bumpers already in surplus storage. One note for replication is that this high cost could be replaced with a low one by using machine screws to the stop the pvc arms in the same manner as the bumpers
- Bike Shifter: ~40. Our bike shifter is the main element to our user interface and generation of energy. The bike shift is relatively expensive and can generally not be bought for less than $40. For our project a bike shifter was already available to us and did not need to be purchased.
User Test PlansOur user test plans detail what data we will be collecting from actual potential user groups. These were designed based on our use cases and engineering requirements, focusing on the aspects of the device that are most important to the end user. The living user test plans document can be viewed here.
Subsystem Test PlansOur subsystem test plans detail what data we will be collecting from individual subsystems, to ensure that they perform the way that we designed and expected them to. The living document can be viewed here.
Inputs and Source
Outputs and Destination
- Report that summarized the degree to which Eng Reqs are satisfied.
- Assessment of accuracy of feasibility models.
Risk AssessmentOur Risk Assessment was updated during phase 4 for any mitigation of risk or newly emerging risks.
The most significant changes we made to risks during this cycle were the additions of the following risks:
After these additions, the risks that are currently our highest priority are
- Our proposed designs and details are too complicated
- The lower extremity attachment is functional, but not usable (slow to attach, cumbersome, etc)
- The ball will not be centered before launch. If the ball is too far off center, it may fail to launch altogether
Engineering RequirementsOur Engineering Requirements was updated during phase 4 for newly Engineering Requirements an update.
The most significant changes we made to Engineering Requirements during this cycle were the additions of the following Engineering Requirements:
- The main update one is the time to set up was change form less the 60 seconds to 60 to 120 seconds; the others are new ones.
Design Review Materials
- We have created an informed consent document which we will use when we are recruiting individuals to participate in our user testing. The document is an overview of what our project is, what we will be testing for, and what risks and benefits the users may face as a result of participating in the research.
- Our presentation may be viewed here
Plans for next phaseA high-level plan for MSD II has been drafted and documented, and can be found here. In essence, MSD II is broken down into segments that will enable the team to realize the designs we have finalized in MSD I. The focus of the work will be on building and testing subsystems and the full system, testing our finished product with user groups, and putting together a polished portfolio of all of our designs, documentation, and recommendations for the future to be handed off to our customer. Additionally, we will plan and prepare for Imagine RIT, where we will showcase our final prototype to the community. The rest of this semester will be spent cleaning up any open documents that will be a hindrance to our ability to move forward in January, such as engineering requirements, test plans, and our bill of materials.
Additionally, each team member has outlined anticipated individual plans for Cycle 1 of MSD II here. These individual plans were based off of the high-level MSD II plan discussed above, and are subject to change due to new learnings about the cycle's expectations.