Weekly Update: Competition and Final Update

Figure1: View Of Cad of Final Machine



Figure 2: Our Machine In Competition

Our final machine ended up placing fourth overall in the “slot-bots” competition this past Thursday. For those that could not see our machine, it involves a cart module allowing us to drive back and forth, with an arm that travels vertically via acetal gear and nylon rack allowing us to reach the hard to get ping pong balls. The end of our arm, there was a rotating scoop driven by a motor in the cart that turned a stainless steel shaft with bevel gears rotating the scoop. On the front of our cart module we had our defensive module which was a wall that helped constrain the vertically moving arm. As the arm travelled downwards a switch on our wall released the wall flaps made from delrin and mesh, where two torsion springs expanded our wall outwards. The final rear defensive module was a very basic wall made from wood, used to protect our rear container.

Figure 3: CAD Model of Machine Showing Shaft Module

During the competition, out team decided not to use the wall flaps (zip tied together) or the rear defensive module, so that we could have a larger initial offensive move without violating the rules of the competition (No defensive moves first). We used a large amount of aluminum on our cart and welded a significant portion of our machine while using very high torque motors. This combination allowed us to push nearly every machine out of our way to score ping pong balls. Despite having technical trouble (A stripped Set screw in the motor) during the first round of competition, we came back and achieved a fourth place finish.



Our final design of our machine did not vary a great deal from our initial design. The biggest variation was the attachment of the torsion springs to the wall. In our CAD model, our torsion springs were just sitting between the wall and wall flaps. During the final week, we determined how to attach the torsion springs using extended hinge rod, and turned out to be successful. One other component we had trouble with was the timing belt we used as treads. The timing belts turned out to be very taught, and we had to manufacture new, offset bushings for the rear axle to accommodate the timing belt properly. It worked out well for us, providing extra traction on the arena.

Figure 4: CAD Model Showing Hiden Lines (Shows Timing Belt Pulleys, shafts, Acetal Gears)

The wall module seen below was modified slightly in the manufacturing process as well. Originally made from aluminum, we decided to save weight, and not make our cart as front heavy, so used a combination of delrin, acrylic and mesh. Finally, the last modification we made, that has been talked about in previous posts was the bushings. Originally planning on using delrin bushing, we sought something with less friction to use, and turned to Teflon. The Teflon bushing worked very well for our purposes letting our shafts turn well and being very low friction.

Figure 5: Wall Module Made from Delrin, Mesh and Acrylic

Overall, the competition was fun and we are happy with our finish. Despite some big and small problems arising throughout the semester, we pushed through and had a working machine for the competition, pulling out a top five finish.

Figure 6: Read Defensive Module that was not used in Competition

Video Update

(Music: TNT by AC/DC)

Weekly Update: Completing the Machine

This past week was spent completing our machine and preparing it for testing on the arena. Due to exams and assignments, our group was really only able to meet from the middle of the week until the end of the week during nights. All of the modules had to be completed, and assembled.

Figure 1: Cart Module Being Assembled After Welding

The rear defensive module had been finished with the exception of being painted, as well as the shaft module (most critical module). A significant protion of time during the late week was spent manufacturing and assembling the wall module. One problem we ran into was the motion of the torsion springs could not be held by simply epoxying them onto our wall. We decided to extend our hinges on the module to house the torsion springs as well. You can see this in Figure 2 below of our wall module.

Figure 2: Wall Module Complete (Torsion Springs Below Hinges)

The weekend team meetings were spent assembling the cart and making sure eerything would work when the motors were attached. Some bushings had to be remanufactured because of problems fitting the shaft. While waiting for the cart to be welded together, our team decided to paint our rear defensive module as shown below.

Figure 3: Rear Defensive Module Painted withName Team

While we still have some work to do on the cart module, most of our remaining work is assembling the entire machine. There are a lot of small pieces that still need to be incorporated into our machine that will take a lot of time. The machine should be completely assembled by the end of the night, and ready for testing in the morning.

Figure 4: Pieces of Last Motor Waiting to be Assembled

Weekly Update: Updated Schedule and To-Do List

This past week was the lead up to Thanksgiving Break and the due date of the demonstration of our most critical module (Shaft Module) and the completed engineering of the rest of our machine. Due to the number of parts alone in our most critical module, and other modules, the pat 5 days were spent mostly manufacturing parts and assembling the most critical module. Our group often had to meet late nights in the Wilson center to assemble and manufacture the machine. Our most critical module and cart module both requre a significant amount of welding, which only one person on our team is able to do properly. Therefor, the Wilson Center was the ideal place to meet for our team.

Figure 1: Nathan Welding Cart

One problem we ran into, while manufacturing was that the polyethylene bushings did not work well once they were press fit into the pieces. They often got pushed out and did not provide a great low friction surface for our shafts to turn on. We decided to invest in brass rod from ALRO and turn that for some of our bushings. It seemed to allow our aluminum and steel rod to turn much more easily.

Figure 2: Checking Fitments On Cart Module

Now that our most critical module is complete, as well as our rear defensive module (shown in previous post), we can concentrate on constructing the cart module and wall module, assembling and testing our machine. In the next week we will be spending all of our time completeing these tasks to have our machine operational by the seventh of December.

The schedule that was created in the first post has been updated from November 30 until the end of the semester. The schedule includes dates to have team milestones completed, meeting times, and machine shop times. Sticking to this schedule should likely allow us to complete our machine on time and be competetive in the competition. Below is the link to our teams updated schedule:

http://spreadsheets.google.com/ccc?key=tGPqXjzlZHqSdRDEU3oI4jw&hl=en#

Weekly Update: Assembling Most Critical Module

The past week our team had several exams and needed to balance manufacturing with other work. The previous week we had done our first stage of manufacturing and completed more than three completely manufactured parts. This past week was used to start assembly, finish manufacturing, and fix errors in our most critical module.

Figure 1: Dimitris and Nathan Manufacturing Shaft from Most Critical Module

Our most critical module, as descirbed in previous posts, is our shaft module used to lift, move, and deposit the ping pong balls on our opponents side of the arena. After use of the waterjet last week, we had finished all of the small parts such as our scoop carriers and our shaft constraints. This past week we aimed to assemble most of our shaft module.

Figure 2: Milled Shaft for Most Critical Module

While looking and developing our assembly we noticed that the aluminum rod given in out kit, was not perfectly round and had tolerances we were not comfortable with. Another visit to ALRO was made to buy a precision steel rod that we could use instead. We opted for this instead of turning down the aluminum because the steel is also much more stiff, and there is less chance of breaking when lifting all of the ping pong balls.

Figure 3: Rubber Tracks, Bevel Gears and Polyethylene our Team Purchased

Throughout the weekend, our team met to assemble the most critical module. The shaft constraints were fixed inside the square tube, and the polyethylene bushings were press fit into the constraints. The scoop was also formed and attached. The final key part that was missing from our module, were the bevel gears which we had ordered on Tuesday this past week. The bevel gears arrived on Friday and everything was ready for the final assembly.

Figure 4: Rear Defensive Module Completed

Sunday Night should be the conclusion of the assembly of our most critical module and our team will use class times and evenings this week to conclude the engineering of our final project. This upcoming week will be busy due to the work we will miss over Thanksgiving break.

Weekly Update: Manufactured Parts

This past week, our group achieved a lot despite not meeting a large amount. Coming into this week, we knew our three manufactured parts had to be completed due to our teams schedule in the upcoming week. The motor lab was also due this past Friday as well creating more work for our team to accomplish.

Despite having a finalized design as of last weekend, some of our team members went to look for scrap pieces of metal, gear and other materials. 1/8" aluminum was purchased as well as UHMW polyethylene (Ultra High Molecular Weight Polyethylene). The aluminum was neccessary for our design, and the UHMW was found for a discounted price, and would work better in certain parts of our machine than the delrin (i.e. motor constraints and to drive the treads).

Our group reserved time for the laserjet early in the week so that we would laser cut our delrin bushings and other delrin pieces as well. Since we needed three different materials and three different processes, we also went to see about the waterjet, to cut out our aluminum parts as well. Using the laser cutter, the pieces neccassary were cut from the delrin sheet. We also cut our our pieces from the 1/8" aluminum, 1/4" aluminum, and UHMW polyethylene. Below are pictures of some of the parts after being cut.

Figure 1: UHMW Ployethylene and 1/8" aluminum cut on Waterjet

Figure 2: 1/4" Aluminum Pieces Cut on Waterjet

Weekly Update: Finalized Design

Throughout the past week our group has met several times to finish engineering out arm and shaft module (See Post 1). After completeing our finalized CAD design and analysis we ran into a couple problems. The first of these problems included how we mounted the motor to the top of the shaft. Figure 1 shows the Solidworks model of the shaft constraints. There are several of these plates that we will manufacture to support the motor inside. Theses will be made from delrin and will be able to slide up and down the shaft on the wall module (See post 1) easily. The second problem we ran into was the alignment problem with the bevel gears (Figure 2; located at the bottom of the shaft to articulate the scoop). We decided to make the bevel gears larger to confront this issue, and also added a cover to protect the bevel gears as well. The bevel gears will be ordered from either McMaster or SDP-SI.

Figure 1: Motor Constraints

From our analysis we found that the gearing specs from our kit would provide configurations offering far too much torque [that took too much time] or far too little torque. Our group decided on swapping some of the gears from another motor kit to achieve an ideal gear ratio. After addressing these problems our group came up with a bill of materials, detailed manufaturing plan, and drawings of all parts in our shaft module.

Figure 2: Bevel Gears Located at Bottom of Shaft

This coming week we will be completeing the motor lab assignment that will be due while using our time to begin manufacturing. We hope to have three manufactured parts completed by the end of this week. A significant amount of parts being manufactured from our shaft module can be made on the waterjet. By reserving the waterjet we should be able to start and finish manufacturing several parts in an efficient manner. We hope to be able to reserve the laser cutter as well to get a head start on our manufacturing. Our original meeting plan and schedule from post 2 should be a sufficient amount of time to complete all of the assignments. The goal of our team is to manufacture all of our parts efficiently and effectively so we can assemble and test our machine to fix any problems that may occur. Having a buffer period of time to improve upon the performance of our machine is important to us.

Figure 3: Finalized Shaft Module