From February 4-17, we have been working to address our fabrication problems regarding drilling holes and attaching the members. One of our team members gained access to a drill press and got machining help, which made creating the right size holes much easier than our earlier attempts, as seen in Blog #5. The rest of the square steel tubing was cut to the right lengths to make up the prototype’s members. The overall structure of our prototype was assembled and attached using nuts and bolts. 4 holes were drilled in the top steel bar and the top of the scissor jack so they could be bolted together. Our next steps regarding prototype fabrication are tightening the bolts, attaching wheels to the bottom of the prototype, and possibly shimming/filling the small gaps between the various members. All this progress can be seen in Figures 1-3.
Given our current progress, we expect this prototype to be completed in the next two weeks. We anticipate problems with tightening the bolts because they are often in hard-to-reach places, like within the square tubing. The team will look into gaining access to socket extensions, ratcheting wrenches, and other tools specifically designed for hard-to-reach fasteners if we are unable to tighten our current prototype bolts.
Although we are not currently done with prototype fabrication, other work the team has done addresses future prototype modification based on testing. We currently see two major sources of potential failure: possible tipping and attachment points.
To prevent tipping, we came up with two main ideas and modeled them in SolidWorks to help visualize them. We also made the original CAD model more accurate to scale and to the components we already bought. One was a counterweight attached to balance out the 100 lb. tire the prototype intends to lift, represented by the box attached to the back of the scissor jack in Figure 4. The other idea was extending the bottom legs, which is also depicted in Figure 4.
Two attachment points are of concern: the attachment of the scissor jack to the upper arm and to the bottom of the device. There will be a lot of moment, since the device intends to lift and hold a 100 lb. tire. We currently have four bolts for the upper arm and four bolts for the bottom. If, through testing, we see that this current attachment method is too weak, we may use JB Cold Weld to support the bolts or acquire welding services.
However, all these possible modifications will wait until the prototype is finished and testing begins. The team believed it was beneficial to preemptively think of potential failures and solutions for those failures. Our planned schedule has us completing prototype fabrication by March 9, but our current progress has the team believing we may finish fabricating and get to testing earlier than expected.
Figure 1: Steel Drilling
Figure 2: Prototype Assembly Progress Front View
Figure 3: Prototype Assembly Progress Side View
Figure 4: Possible Prototype Modifications (Counter Weight & Extended Legs)
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