Over the Preliminary Detailed Design Phase, Team 19305 will complete the initial rendering of the electric longboard's folding mechanism, submit our grant application to IEEE, maintain open communication and utilize consultation with our guides, and develop expectations for our detailed design phase. Additionally, the initial parts list and BOM will be created and verified by the team. Updates to necessary documentation, criteria, etc. will be made as necessary and preparation for the detailed design will begin.
A method to individually calibrate the response curve of the force sensor circuit through software was envisioned via adjusting the op-amp reference voltage using a digital to analog converter (DAC).
In order to verify the effectiveness of such a strategy, a mock circuit (image on the right) was created in LTSPICE. Then a DC sweep for the DAC input voltage and a parametric sweep for a resistor (which substitutes for a force sensor with a changing force on it) were run simultaneously.
The results of the simulation clearly demonstrate that software calibration of force sensor range through usage of a DAC is a viable and effective method.
Initial Design
The initial design firm mechanism works for having two pieces that slide against each other linearly, and then translate.
Version 1
To accomplish this, we first sent out by trying to design a mechanism out of commercial off-the-shelf components. Version one of the system used 4 to 1x1" aluminum tubes with a trolley using eight bearings and one linkage to accomplish this task. The mechanism of the hole needed to fit inside a box which measured 10 inches wide by 15 inches long by 2.5 inches deep. Because of this rather small size constraints, version one of this design was not exactly practical. shafts that trolley bearings rotated on were 2 mm in diameter. It was clear after some initial modeling, that this design would have to be iterated quickly.
Versions 2 and 3
Versions two and three of the design focused on sacrificing with of the rail, to decrease the death of the mechanism into the body. This as a whole would increase the volume inside the board giving us more space for electrical components and batteries. To accomplish this we first considered using rounded bearings inside the channel but found that parts for this style of mechanism were not available commercially. From there we then moved to using V groove bearings and rails.
This mechanism was further simplified by using 3 linkages and rails instead of 4. The resulting assembly was modeled using entirely available commercial off-the-shelf components, and can be manufactured as a proof concept moving forward. This design below was intended to be made out of a 2x10" piece of wood for cost effectiveness. Realistically this is shallower in depth and thinner in width than the actual depth of our board, but it does demonstrate how the mechanism would work.
Deck Design and Protyping
Initial Sketch and Michelin Mobility Submission
Our initial sketch of the board showcased a few of his features as well as the intended folding mechanism in a coherent design.
Initial CAD Modeling
From there the board was modeled to somewhat parallel the sketches, but ultimately the modeling strayed away from the design aspects that were most important. The model intended to use a deck lid and under tray system for attaching the electronics. This type of system would not work with the folding mechanism so the design had to be reverted back to its original sketches to focus on a unibody design.
Foam Modeling
After drawing a few sketches on paper, we began cutting and foam. A foam model gave us a tangible part and test some of the early ergonomics of the board. The board was thickened to accommodate for internal electronics, and the sculpted for an athletic form factor.
Next Steps
Once this foam model is finished, we will begin modeling it in CAD. Our intention is to build this board as one uniform piece, as a testbed for the electronic systems. Following this we will then build a second board in multiple parts that incorporates the folding mechanism. The intention for this plan is a risk mitigation to avoid the bottleneck of workflow. Since the folding mechanism is relatively complex and can be proven on a different testbed, it makes sense to separated from the design for now with the intention to add it in later. If the folding mechanism does not function properly it can be replaced by simpler mechanisms such as hinges.
Rolling Cam:
Cams can be tailored to fit specific riding dynamics by changing geometry
Base Plate:
Mounting positions for New and old school mounting patterns.
Adaptable for different hanger mounting angles
Minimal complexity allows for 3-D printing and injection molding
A link to the live Parts List and Bill of Materials can be found here.
| Risk Category | Risk | Cause | Effect | Risk Prevention | Contingency Plan | Likelihood | Severity | Importance | Owner(s) |
| Technical | Failure of Force Sensors | Damage to sensing surface or blocked transmission of force to sensing surface | Complete loss of motor control/unexpected motor response | Thoroughly test force sensor installation | Use remote to control motors | 3 | 9 | 27 | Matthew G. |
| Technical | Control system causing unexpected outputs (malfunction) | Incorrect inputs were put in the system | Incorrect Outputs/System Failure | Have at least one other team member monitoring the inputs made to the system | Have a micro-controller system expert look over the system | 1 | 9 | 9 | Matthew G. |
| Technical | Electronic components protection | Exposure to external environmental factors (water,rocks, etc.) | Damage to the battery and other components | Ensure proper location and protection of electrical components. | Have a guide for a particular environment that must | 1 | 3 | 3 | Kristin O. |
| Technical | Product failure or part malfunctions | Miscalculations during design process | A non-functioning product | Mechanical Design Leads must be consulting each other | Consult with Mechanical Engineering Professor. | 3 | 9 | 27 | Tanvir M. Connor F. Erik L. |
| Safety | Pinch points in the mechanism | Folding Mechanism | Damage to hands and fingers of riders. | Proper outlined guide for Hand Placement | Wear protection gloves | 1 | 3 | 3 | Tanvir M. Connor F. Erik L. |
| Safety | Motor failure | Low resistance and Electrical overload | Corrosion of the motor shafts, bearings, and rotors | Determine the full specifications for what type of motor we are looking for | Invest in a High quality motor | 3 | 9 | 27 | Deirdre A. Matthew G. |
| Safety | Stability failure | Trucks don't work as designed | Danger to the rider of falling and hurting themselves | Conduct tests of trucks over full range of speeds with differing loads | Find trucks that are stable | 3 | 9 | 27 | Tanvir M. Connor F. |
| Safety | Overall integrity of collapsible parts | Weak focal point | Collapsible mechanism does not have a long life span and the board is damaged after few uses | Determine the best and most applicable collapsible mechanism. | Hinge system | 1 | 9 | 9 | Tanvir M. Connor F. Erik L. |
| Resource | Lack of additional funding (Budget) | Not keeping track of spending | Unable to finish design or a low quality product | Proper documentation of spending | Cut costs where necessary | 3 | 3 | 9 | Deirdre A. |
| Resource | Customer manufacturer quality and accuracy risk | Bad quality deliver | Low quality product | Make sure to order from reputable manufacturers. | Change suppliers | 1 | 9 | 9 | All |
| Resource | Lack of experienced riders to test prototypes or data collection | Lack of exposure to longboard riding | Lack of essential knowledge on the design of the longboard | Have a team meeting for instruction on how to ride the longboard | Interview experienced riders | 1 | 1 | 1 | Erik L. |
| Resource | Team Members Being Absent | Exceptional Circumstances (Sickness, etc.) | Falling behind on deadlines and not being able to create longboard. | Make sure at least one person on the team has a good understanding of what the abstentee was doing, | Assign the another person the absentee's task depending on how important the task is. | 3 | 3 | 9 | All |
| Technical | Folding Mechanism Roadblock | Complexity in Design and Material Scarcity | Can't integrate all essential parts and can't proceed with the design. | We build a functioning prototype without a folding mechanism (mule). | We design a different folding mechanism into our mule based on hinges. | 9 | 9 | 81 | All |
| Resource | Not Being Able to Design PCB Board | Lack of experience with PCB design. | Non-functioning PCB. | Try to find a professor to help verify. | Buy VESC. | 3 | 9 | 27 | Matthew G. |
For the Design Review - Our group presented on the preliminary thought out design of the longboard folding mechanism. The different components were done out in solid worlds in order to see how feasible the design would be. With the image of the design was for the most part figured out, we then are able to see how much space the team has for electronic components on the bottom of the board.
The handouts from this presentation include a Gantt Chart of the next phase (shown in "Plans for Next Phase" section), a preliminary BOM, the updated Risk Assessment and simulation results.
Link to presentation: https://docs.google.com/presentation/d/10yMmbIplZ-W_GsOjOuANn_XHnSXs6BNdp_rOG7DEFyw/edit
Action Items:
Figure 2: Plans for Phase 4
Individual Plans:
Connor Ford's Plan
Erik Lydick's Plan
Tanvir Majlish's Plan
Kristin Ostiguy's Plan
