Team Vision for System-Level Design Phase
- Create a strong vision of the final system architecture through the creation of a detailed Functional Decomposition
- Buy down high risk items for each sub system through the use of analytical tools.
- Decide on the make up of high level systems
- Determine if overall project budget is reasonable
- Determine if Engineering Requirements set forth are achievable
Addressing Issues from Problem Definition Phase
- Clarify the responsibilities of the FSAE team and the MSD team.
- Remake the WBS
Full System Overview
Old revisions: /public/Systems Level Design Documents/func_decomp.jpg
HW/SW High Level Block Diagrams
Concept Generation and Selection
1. The tolerance on position is based on the wrap angle tolerance and the distance from the centerline of the tube being manufactured. The worst case tube manufactured by the FSAE team is 0.375in in diameter and would have a wrap angle of 89 degrees. Figure 1 shows a general schematic of the geometry of the cross feed and spindle relationship. Based on the geometry of the setup, the linear move per wrap is 0.0228 inches. To meet the wrap angle tolerance of one degree, the maximum move per wrap can be 0.0435 inches and the minimum move per wrap can be 0.0207 inches per wrap. This means that the total distance tolerance is 0.0415 inches per wrap. Table 1 shows the derivation of this tolerance. The most common step size of 1.8 degrees was then assumed and the size of the pulley on the output of the motor was used as a tuning tool to find the linear distance per step.
2. The torque required by the motor is dependent on the allowable distance to accelerate the cross feed assembly from zero inches per minute to the maximum required inches per minute of 325 IPM. By using basic kinematic equations and finding the necessary tension force to accelerate the mass of the cross feed assembly, the motor torque can be found. Table 2 shows the derivation of the required torque. The pulley radius is an adjustable part of the system to obtain the required tension.
3. The maximum required RPM of the motor is dependent on the size of the pulley attached to the motor and the maximum possible 325 IPM. Table 3 shows the derivation for the minimum RPM of the motor assuming a 2.5 in pulley used in the calculation of necessary torque.
4. The cross feed will need two motors. One motor will be used to move the Z-axis, and the other to adjust the X-axis for different size tubes. Table 4 shows a few motors that meet the minimum requirements for questions 1 through 3 and their corresponding prices. As a percentage of the overall team budget, stepper motors could potentially cost 11% of the budget.
5. Table 5 shows the cost per unit length of different drive types.
1.1 Technical Feasibility: Will carbon spool packaging form factor allow for simple mounting adapter?
1.2 Feasibility will be determined via benchmarking spools of carbon spool manufacturers to determine general geometry.
1.3 Carbon spool geometries were researched to determine the packaging form factors. Carbon spools were researched from the following carbon fiber manufacturers: Rock West Composites Easy Composites Hexcel Toho Tenax All of these companies used a similar packaging which is a cardboard or plastic tube to support the wrapped filament. This similarity between all carbon spools allows for a simple mounting adapter that spools from different vendors should be able to slip onto.
2.1 Cost Feasibility: Will a tensioning mechanism be feasible within a reasonable cost envelope?
2.2 Feasibility will be determined by calculating a rough cost of a worst case number of rollers and tensioning mechanism. Component cost research can be used along with further cost analysis to tackle this financial resource risk.
2.3 Keeping tensioning method completely mechanical with very few components while also using a roller system will keep cost very low. The following components and cost/component (or material) are outlined below. This is a worst case amount of components/materials: Grade 8 nut+bolt+washer for spring loading mechanism Average combined price: $1.00. 3d printing plastic adapter for spool mounting: Free. RIT Makerspace or Brinkman Lab (team provided resource). Rollers, Quantity 10
Worst case: Supplied from vendor, $20 each
Best case: Machined in RIT ME Machine Shop with team provided material, $0 each
Compression spring Average cost: $0.58/spring Spool mounting structure
Worst case: Purchase all material, $9/ft 6061 aluminum Stiffness not an issue so lowest mass of most available material chosen
Best case: Machined and welded in RIT ME Machine Shop with team provided material, $0 total. Total worst-case cost with very conservative material estimations: $211 Just over 10% of project budget. Cost is feasible.
3.1 Technical feasibility: Is a low maintenance tensioning system feasible?
3.2 Feasibility will be determined using logical assumptions based on function and loading of system.
3.3 The spring-loaded method used to apply a spool torque (2lb*spool radius) will be be a very low wear item. The preload (normal force) between the spool adapter and the spring-loaded mechanism will be very low. The runtime of a tube combined with the low spindle speed and preload will cause extremely low abrasive wear, meaning this mechanism will likely not be a wear item. Plus, a longer and softer spring will allow for forgiveness for microns of wear. Rollers will not be a wear item as they will be very lightly loaded and serve the basic function of guiding the fibers.
4.1 Technical Feasibility Will the system be able to hold spool capacity?
4.2 Feasibility will be determined by benchmarking spool weights and logic.
4.3 Carbon spool geometries were researched to determine the expected mass of a spool. Carbon spools were researched from the following leading carbon fiber manufacturers: 12k Rock West Composites-3.3 lbs 12k Easy Composites-10 lbs 12k Hexcel- 8 lbs 12k Toho Tenax-3.1 lbs
Benchmarking shows the heaviest general 12k carbon spool that this machine will have to support is 10lbs. Even with a large factor of safety on this load, supporting the spool will be a non-issue with the materials available for the spool mounting structure. Even with basic aluminum or steel, a simple structure can be designed to hold thousands of pounds, nonetheless 10.
"One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips and sparks. Examples of guarding methods are-barrier guards, two-hand tripping devices,electronic safety devices, etc." OSHA 1910.212(a)(1)
Bringing It All Together
Overall Cost Analysis
Goal: The goal of starting to model the system is for us to understand how we will package and bring together the selected concepts.
- Beginning Modeling as part of next phase
- PTC Creo as modeling software
- File name convention:
XX - Subsystem name:
TN - Tensioning
CF - Crossfeed
DR - Drive
FR - Frame
EL - Electronics
YYY - Part number:
001-300 Individual part files
301-801 Higher Level Sub-assemblies
901 - High Level Sub-assembly
-Common coordinate system
- Origin at center of drive spindle nose.
Cost Mitigation Plans
- Standardize and reduce the use of unique fasteners on the machine
- Design motor mounting to standard NEMA sizes based on feasibility analysis. Competitively price motors that fit form factor and meet
- Raw material - Utilize existing surplus and scrap material the Formula Team currently has
- Sponsorship - Inquire on companies donating high cost items to the team through their 501 (c) status
- Manufacturability - All manufacturing operations can be performed in-house