Week 9:
The group has received our extra setup from Dr. Konstos's lab for testing or presentation. The group met this evening to work on the final report after completing the final quad chart during class time. The group plans to meet again tomorrow evening to finish the last sections of the report and polish everything, ensuring it complies with all formatting and other requirements. The group is excited to present at next week's Freshman Design Competition.
The group printed an extra main housing, rotor, and eccentric hub in Dr. Konstos's lab to use for the presentation as well as to have a backup if we fail another compressor assembly during testing.
We received the new, revised main housing this past Friday. We also completed several tests including volumetric flow and air-tightness testing. At the end of the air-tightness testing, the assembly was very obviously melted and broken.
The reason the assembly melted is due to the speed we were running the compressor at (~1600rpm) and the friction caused temperatures inside to exceed the melting point of the PLA filament (65C). Luckily, we had already planned on making another, revised assembly and had submitted for the main housing already. We have now submitted print jobs for a new, revised eccentric hub and another rotor, this time with the optimized lattice, again.
Week 8:
The print shop returned our fourth print of the rotor today-it came out perfectly. During the group meeting in the evening, David and Will disassembled the previous prototype and reassembled it using the new rotor after sanding down the edges somewhat. During testing conducted in the Innovation Studio, the updated setup produced a reading of ~9 PSI on our pressure gauge and inflated a balloon successfully.
Week 7:
All parts have arrived, a working prototype has been assembled, static simulations using Fusion 360 have been completed. The 3rd iteration of 3D printed rotor has been received but has several problems. A 4th and final iteration will be sent to the print shop and will hopefully turn out as desired. Plans for the coming week include polishing our Final Report and beginning work on our final presentation while we test the prototype and wait for the new rotor.
The fault with this rotor is that the printer adjusted the thickness of filament printed and under-extruded the filament. This makes the rotor very light with less structural integrity than designed for, and rather porous (not good for an air-tight mechanism).
Left: rotor during the printing process (credit Gavin); Right: finished rotor with epoxy modifications
Due to the porous surface of the rotor, it was coated with a layer of 4-minute epoxy that the group purchased to seal the hose to the main housing. This sealed the surface well enough that the group was able to assemble the prototype air compressor to conduct a test run using a balloon to test effectiveness.
This test was run without the check valve or pressure gauge to give a basic idea of the volume of air compressed and to prove that this design is feasible. Before the test, all moving parts were given a light coating of Silicone Lubricating Grease (with PTFE) to allow for smoother movement and increased air-tightness. Though the current effectiveness is low, David has already begun looking into the reason and potential design improvements. As of now, he has already identified that the rotor we received from the print shop is slightly undersized due to the under-extrusion of the printer during the print process. We will be submitting a fourth design iteration to the print shop with slight size modifications and without the optimized latticing to (hopefully) receive an exact, finalized piece for our compressor.
Over the weekend, we received the second rotor from the print shop, the print was a failure. We were still able to assemble the entire prototype using the failed print to show what the final design of the compressor should look like. The problem with the print is the lack of walls around the rotor, causing it to not be solid and airtight.
Additionally, the internal gear teeth were offset about halfway up their length causing the rotor to not mesh and rotate properly within the main housing. This is most likely due to the print shop using Afinia Studio as the slicing software. The software did not recognize the wall geometry. We are unsure about why the gear teeth were printed incorrectly. The part was resubmitted to the print shop without the customized latticing so they can add their own internal structural supports and (hopefully) successfully print it with wall and straight gear teeth.
The group has begun work on the final report, we plan to meet Wednesday night and have a polished draft completed by Friday to turn in during lab. After the draft has been completed we plan to have another group meeting to finalize plans on what tasks need to be completed by the end of Week 8 and plan out where we can improve the final report and where we need to compile more information. We also need to begin work on the final presentation.
Week 6:
Will used a lathe to turn down the diameter of the 5/8" aluminum rod to 3/8" to create two more craftshafts of higher quality. As all of the mills were in use he was unable to use a mill to create the square and hexagonal ends on the crankshaft. He will complete that task when he next has free time within the next two weeks. Hieu has begun running simulations on the CAD file testing stresses, pressures, and torques.
David received the acrylic from McMaster-Carr and we were able to laser cut the lid today. David then did a mock-up of the final assembly (without the rotor) to check the entire compressor. The hole in the lid for the crankshaft needs to be reduced in diameter by a small amount, the exact amount will be determined based of the diameter of the unfinished crankshafts that Will is machining, as those will be used for the final assembly.
The first print of the rotor was received from the print shop today-it was a failure due to a miscommunication. David specified in the .stl file not to add any extra internal support when printing the rotor, however, this was disregarded. The print was stopped once it was realized the print was taking much longer than originally expected. We were able to take the faulty print, it's about 1/8" thick.
Will received the correct part from Amazon after being shipped a pressure relief valve instead of a ball check valve. During lab, the basic layout for the hose and all valves and accessories was drawn up by David specifically for the blog.
Will used a lathe to turn down the diameter of the 5/8" aluminum rod to 3/8" for 2 more, better quality crankshafts. The mills were in use by others so he was unable to mill the square and hexagonal ends into them.
Week 5:
David used Autodesk Netfabb to generate and optimize a lattice for our rotor. The rotor was optimized to reduce volume while maintaining acceptable stress levels for PLA (our 3D print material). This created a lattice of variable density in the outer regions surrounded by a layer of skin, also of variable density.
The crankshaft was turned and milled today in Drexel's machine shop-it's a little rough, but that's fine for a prototype. Additionally, the rubber sheet was cut to fit the housing and we received the eccentric hub from the print shop. This allowed us to test fit the crankshaft to the hub, and it's a perfect press-fit.
The rotor and eccentric hub .stl files were submitted to the print shop last night, we should be receiving the prototype prints within the next few days. Will took the scrap wood selected for the baseboard to the Innovation Studio to clean it up, cut it to shape, and sand it down. It looks significantly better now. Additionally, Will spent 2 hours taking all of the raft
off the bottom of the main housing prototype and drilling out the screw holes.
Will used the 3D CAD model to create a part drawing of the crankshaft for machining. Below are pictures of the original part drawing and the revised one created after he consulted a friend in Drexel's Formula Society of Automotive Engineers team who had much more experience with part drawings.
For our rotor, Autodesk Netfabb Optimization Utility was used to generate and optimize a functionally graded lattice. The lattice used a hexagonal cell structure and was used for the outer regions of the rotor. The rotor was optimized to minimize volume while maintaining acceptable stress levels for PLA (our print material) while under 400 kPa (4 atmospheres) of pressure. This created a lattice of variable density in the outer regions, surrounded by a layer of skin, also of variable thickness. This allowed for a very uniform distribution of stress throughout the component, with no dangerous stress concentrations.
David has completed a CAD design for Prototype #2. Revisions were discussed and decided on during our weekly meeting. Other topics for the meeting were finalizing the list of parts to order, how the deliverable should be presented, and the Project Proposal Presentation that is happening on Friday, April 26. David has stated that he hopes to have the final CAD file for the project completed with the revisions by this coming Friday. This would allow us to move onto the next phase of our project: analysis within the software, and manufacturing and assembly of the physical compressor.
For the presentation of the final deliverable, the two main points were about how to attach the main housing to a base board and how to attach the lid to the main housing (as well as what material the lid should be made from). The final decision was to design tabs on the main housing that would have space for screws to secure the housing to the base board. The lid will be secured to the main housing with screws, and the lid material will depend on whether the group has access to a laser cutter or not. If we do, then the lid will be made from acrylic, if we do not, the lid will be 3D printed.
The group also worked on the PowerPoint slides for the presentation on Friday and created a strong outline with some of the details. Presentation planning will happen more after the lecture on Wednesday, April 24.
The group finalized the list of parts to order and the order was placed through Amazon. These parts should be arriving within the coming week. Once they arrive manufacturing can begin.
Today was a milestone for the project-we received our first prototype 3d print from the print shop, and the aluminum rod being used for our crankshaft was delivered. The rest of the materials were also received today so assembly can begin when the group meets next. Will needs to find time to get to the machine shop, so turning and milling the aluminum rods will most likely begin next Friday, May 3.
David designed an updated prototype of the basic Wankel Engine configuration the group has discussed using Autodesk Fusion 360 (shown below). During a group meeting, the team extensively discussed the prototype, the component parts, manufacturing methods, required training, ideas for how to run the engine, and refined the planned end result of the project and the result we desire.
The highlights of this meeting included a revised, group-discussed parts/materials list and desired manufacturing techniques for each specific component. Below are some of the final notes taken from the meeting.
Questions/discussion points:
1) How to connect tubing to actual pump (interface b/w pump and hose)
-Hose barb? 3D print onto?-NO
2. How to attach electric motor
-use hand drill w/ socket attachment for appropriate diameter hex shaft
3. How to manufacture different parts (focus on 3D printing)
-Machining will allow for much more accurate parts, but must be less complex (i.e. crankshaft)
· Crankshaft: machining (Will) or purchased as is
§ 6061 Aluminum rod (round or hex) or buy rod, cut to size, finish with machine
· Case (w/ attached central gear): 3D printing
· Central hub(off-center): 3D printing/lasercut
· Lid for casing/frontplate- 3D print/lasercut
4. How to attach lid to case
-Overhanging tabs with holes for bolt&nut
-Holes in case and lid to put screw in
-O-ring around entire case
5. Outlet has to be on side of case
a. Glue into case/cover with a layer of grease
· Pressure gauge w/ adapter to hose (<.5" diameter)
· Rubber pad/O-ring-would need a groove around top edge of case to fit O-ring into
· Bolts & nuts-secure lid to case & possibly case to base of some sort
-Nuts- diameter: (same inner D as outer D of bolt-matched set)
-6061 Aluminum rod (round or hex)
---Connect direct to pressure gauge
-Check valve to allow one-way passage of air only
Prototype V2 design pictures (Left to right): Isometric view of the engine housing; top view with
wire-frame of meshed, stationary central gear and rotating off-center gear; side view of the
assembly with wireframe outline of the gears for depth reference; isometric view of assembly
without lid; animation of the engine working
Week 2:
The group has changed the project plan to designing a basic Wankel engine that can be run in reverse as an air compressor due to information discovered while evaluating the feasibility of manufacturing gears at Drexel. Drexel's machine shop does not have the capability to manufacture gears via CNC, and, CNC has been deemed a cost-prohibitive manufacturing method. The project proposal has been completed and reviewed as of 4/11.
*Edit: Later this week, David modeled a basic prototype of the engine in Autodesk Fusion 360 (shown below)
Week 1:
Group formed and brainstorming for potential project ideas begun. A basic plan is formed to construct a set of planetary gears. The main purpose of this idea would be to test and expand on the manufacturing abilities of the group through the fabrication of these gears.
