Most Critical Module Complete. All Engineering Done

Last week, we finished the manufacturing and assembly of our most critical module, the arm. The remaining pieces to be manufactured were the front plate and the PVC tube arm section. The front plate was water jetted out of a 1/16 in thick sheet of aluminum. The PVC arm section was made primarily using the band saw. Originally, we had planned to use the mill, however, we were told during manufacturing that since it was hollow, the mill would not be a good option as the PVC would move quite a bit during milling.

We made a slight change to our most critical module related to the fasteners. Instead of using the metal bolts we had planned to use to attach the front plate to the arm section, we used plastic fasteners instead. These are lighter and will hopefully allow our machine to operate better. We left one metal fastener where the PVC plug meets the PVC tube to insure that the arm stays together.

Also this week, we finished the engineering of the rest of our machine. In this up and coming week, we have quite a few things to get done. First, we need to cut out the base of our car. We plan on doing this on the water jet machine and manufacturing it out of a 1/2 in PVC plate. Next, we need to manufacture our pillow blocks. We have a total of 12 pillow blocks to manufacture. They will be manufactured out of 1/8 in L-stock. These will take the majority of our time this week. We also need to manufacture 2 axles. One will be for the front wheels and the other will be for the rear wheels. Due to a shortage in supplies, we had to design each axle slightly differently. the back will be a 1/4 in diameter aluminum rod while the other will be a 3/8 in diameter aluminum rod turned down to 1/4 for where it meets the bushings. After that manufacturing is complete, we need to hook up both of our motors to the rest of the system. We have one motor that will be connected to a worm gear box to run the arm and we plan of using a planetary gear box to move the car forward and backwards.

Here are a couple of Solid Works renderings of our completed design:

Calendar

First Three Parts

This week our team manufactured three parts of our Most Critical Module, which is the scoop arm of our machine. The three parts we made were the arm axle, scoop, and a plug used to secure the scoop to the bottom of the arm.

The arm axle was manufactured primarily on the lathe from the 0.5" x 0.5" Aluminum square stock. We started by facing off the end to smooth it out and make it easier to measure. We then took that end of the rod down to a circular cross-section with a 0.25" diameter. Next, we used the band saw to cut the rod to roughly the dimension of our part. We then faced the end off again to give a smooth finish and to give the piece the required length. We once again took the end down to a 0.25" diameter. We then added grooves one each side for e-clips to fit into in order to prevent axial movement of our arm when in use. The next step was to use the mill to drill two holes in the center part of the axle for screws that will be used to secure our arm on the axle. Once this was completed, the final step was tapping each hole.

The scoop was done on the mill and band saw using the 0.25" thick Aluminum plate. The band saw was initially used to cut out a section of the plate slightly larger than the final dimensions of our piece. The mill was then used to square all the corners and ensure opposite sides were parallel to each other. Once this was done, the part was milled down to the correct size specifications. The mill was also used to drill holes in the piece required to attach the part to the rest of the arm assembly. After that, chamfers were cut into the edges using the mill and were then smoothed out further by filling them down by hand.

The plug was milled from the 1" diameter PVC rod. The mill was used to cut the rod to the correct length and also to cut the angled bottom of the part. This was done very carefully using an electronic protractor since the angle of the cut needed to be very precise in order for it to fit with the rest of the arm assembly. Once this was finished, four holes were drilled in the part using the mill. Two of them were blind holes and will hold screws that attach the scoop to the plug, and the other two will be used to secure the plug to the main arm section. The part was finished by tapping the two blind holes.

Below is a photo taken of the three parts near the end of manufacturing. The parts from left to right are the scoop, axle, and plug. The plug is still missing the two tapped, blind holes and the axle is also missing its two tapped holes. The scoop is missing holes as well as the chamfers on the corners. An up-to-date picture of the finished parts will be posted soon.

This next week we will finish our engineering and manufacture the last two parts of our MCM, the front plate and the main section of the arm.

First Manufacturing

Today, we manufactured our first part. Using the lathe, we turned the axle for the arm, our most critical module.

Sunday, November 15

This week, we primarily focused on finalizing the fundamentals of our machine. The axle for our scoop arm will be constrained by two pillow blocks as shown in the CAD image above. The torque from the motor will be transmitted to the arm axle by a combination of a worm gear and spur gear. We chose to use a worm gear for a couple reasons. First of all, the worm gear will greatly increase the torque output in our arm. Secondly, a worm gear cannot be back-driven, so opponents are not able to push our arm back once we have fixed it into a position. The worm gear and worm we plan to purchase are from www.sdp-si.com, and are similar to the ones shown in the photo below. The worm gear we will purchase is made of polymer because our machine does not require one as heavy-duty as steel.

We had planned to have our arm nearly manufactured by this week; unfortunately, the ME250 shop did not have openings, so our arm manufacturing is being pushed to next week. Our goals for next week are to complete the rest of the engineering for our chassis (which is the remainder of our machine) and to manufacture and assemble our arm module. If all goes as scheduled, we plan to have our solid assembled model and drawings for our entire machine completed by the weekend so we can begin manufacturing the remainder of our machine early next week.

This past week our group worked primarily on the MS6 assignment, redesigning our most critical module (our arm). We changed the materials of some of the components to PVC pipe (white components in picture below) in order to minimize the weight of the arm while still keeping it relatively strong; it is now about 1/5 as heavy as the original design (about 4lbs reduced to about 0.8lbs). This will allow us to rotate our arm faster, whereas before it probably would have been too heavy to rotate at all. Another benefit of our redesigned arm is that it does not have near as bulky a design with large unnecessary corners sticking out in crucial areas, such as at the bottom near the scoop. It will still take up almost the entire width of the slot with a flat face pushing the balls, however, to prevent balls from getting forced (wedged) into the walls of the slot and getting stuck, making it more difficult for our arm to continue rotating.
We decided to use the square aluminum rod for the axle by rounding the ends on a lathe in order to eliminate some issues with effectively constraining the axle to the arm section. It will be inserted into a square, interference fit hole in the top of the arm section. The PVC arm section will undoubtedly be our most difficult component of this module to manufacture with the square hole in the top and flat cutout with holes on the bottom half, not to mention the precisely angled cut on the bottom that the scoop piece with be assembled flush to. The scoop section will be attached by a PVC rod 'plug' which will then be attached to the front aluminum plate and PVC arm section. (see images below)