The second “CAD & Rapid Prototyping Competition” of the Mechanical and Aerospace Engineering (MAE) sophomore course in Computer Aided Design (CAD) and Drafting (MAE-94) was held at the end of Finals Week of Fall 2013.
This year Prof. Robert Shaefer challenged the students to design and build a device, which propels itself using nothing but a single rubber band. The requirements were that the device would be designed using a CAD software and then fabricated using only a rapid prototyping device (no machining was permitted). The device could not be larger than 0.10 x 0.10 x 0.25 m3 and must travel a minimum distance of 0.5 meter on a flat surface using nothing but the potential energy stored in single rubber band. Additionally, the teams were told that following demonstration of their device a competition would be held to determine the top three performing designs based on the longest distance travelled. The top three winning teams would receive a “Certificate of Winning” and extra credit towards their final grade.
To promote cooperation and build camaraderie among student team members the class was divided into 23 teams with 2 students per team. First, a conceptual design was developed and presented and on the day of competition a Final Design Report was handed in, which included rubber-band energy analysis, assembled CAD Solid Model of the device, and engineering drawings of all the parts as well as testing and evaluation analysis of their final product along with fabrication experience gained during construction. Despite the many setbacks caused by malfunctioning of the MakerBot® printing devices, 19 of the 23 teams successfully built and demonstrated their device on the day of the competition.
The students were to use a rapid prototyping device, which is capable of replicating a digital CAD solid model into a free-standing 3-dimensional (3-D) structure made of plastic, such as ABS (Lego® plastic). The devices are generally called “3-D Printers,” because similar to an inkjet printer they “print” an object by continuously depositing a fine string of molten plastic, layer by layer resulting in a 3-D object. The 3-D printers for this project are desktop printers, which are not designed to operate for extended number of hours. The MAE-94 demand on the printers surpassed the performance capabilities of the printers and thus students had to suffer innumerous setbacks during fabrication of their parts. Despite, the many 3-D printing delays and setbacks, 19 of the 23 teams succeeded in fabricating their devices. The remaining 4 teams were given permission to fabricate their device using conventional materials and to use the student machine shop.
The “printing” experience was everything but smooth. Because this was the first time the new Rapid Prototype devices were being used (they had arrived just weeks before the quarter started), a number of unexpected performance issues had to be resolved. However, the students were persistent; some teams spent as much as 8 hours in the CAD lab to produce just a single part. Several teams had to redesign their device, due to the limitations of the “printer” and some had to redo their parts due to unexpected fabrication flaws.
On the day of competition, Dec. 13th 2013 (last day of Finals week), 23 eager teams gathered in the CAD LAB (38-138 Engineering-IV). They displayed their products and demonstrated the performance of their device by “charging” the rubber bad; either winding it up on an axle, pulling it, or twisting the rubber band. Almost all teams showed that their device was designed and built within required design specifications, and where able to travel the required distance of 0.5 m, thus fulfilling all high-level design requirement. Following the demonstration the competition took place. The large variety of designs resulted in a wide spread in traveled distance. Because several parts were made of low-density ABS-plastic (faster printing speed), some of the devices failed during multiple attempts to break the record. In the end, the first place-winning device traveled a distance of 48 feet, the second place winning device rolled about 37 feet, and the third place distance was about 27 feet.
Because some of the devices were able to travel distances longer than the 38-138 E-IV room, the competition was moved to the hall way. As a result of the commotion and cheers of participating teams, the vice-chair of the MAE department, Prof. Adrienne Lavine along with other faculty members were drawn out of their offices and witnessed the competition first hand. Judging from the excitement among students and faculty, it became apparent that the competition at the end of the quarter was a great celebration of the students’ hard work.
In the end, the process of concept innovation, designing and modeling of parts, overcoming fabrication challenges, re-designing, and spending a lot more time manufacturing than originally anticipated, gave the students the opportunity to experience a near real-life product development process.