Final Team Design

The telescoping arm module changed slightly over the course of the class. Our initial concept was rudimentary and did not consider how we would manufacture the components, or how we would attach the separate elements together. One of the biggest conceptual changes, however, was the addition of a deployable ramp which would make it easier to deposit balls into the slot to score. Previously, the ramp leading to the telescoping tube was only as long as the base plate, giving Wall-E only 8” or so of room to score balls into. This was expanded to cover the whole slot, more than doubling the scoring area, making it easier for the driver (and thus faster) to score.

As previously mentioned, the initial concept did not accommodate for the manufacturability of the arm. One of the key elements was the delrin sleeve which hung underneath the base plate; no companies made square delrin tubing, it would be obscenely expensive to buy a block of delrin in the correct size and machine out the middle, and we had no injection molding capabilities in the undergraduate shop. Instead, the design was changed so the tube was made of four different plates of delrin, each laser-cut in a tongue-and-groove fashion to fit securely together. These parts were then epoxied together.  An additional advantage of laser-cutting the delrin plate was that the arm could be easily made to the correct angle- had this angle not been within the tolerances, the aluminum tube would not have been able to properly block the flipper.

Overall, the concept of the car stayed the same throughout the semester though we had to make some adjustments as the manufacturing process went on and as we took the competition rules and options into deeper consideration.  The first design change came when we attempted to bend the brackets in the student shop for the roller arm and the walls of the hopper.  We realized that the bender was very limited in capabilities and unfortunately the bends that had worked nicely in Solidworks were not as practical in manufacturing.  To address this problem, we simplified the bends for the hopper walls and changed the brackets to a simple bend and two by one stock to support the roller arm.  Once we put more thought into mounting the double gearbox and the battery we found that it would be best to extend the base plate of our car and make the hopper slightly smaller.  The drive train was then moved from beneath the hopper to accommodate the larger wheels given to us in the kit, and to prevent the angle of the hopper from becoming too large. Once we adjusted the base plate, we decided that the motor for the roller would be mounted above the base plate extension on the back of the hopper and that we would use a timing belt from the motor to the roller axle to spin the roller.

Our final car functioned using the rear wheels to push the car while the front of the car slid across the carpet.  The plate that slid across the carpet was made from delrin to reduce the friction between the contact point and the carpet.  In the competition, a rubber band belt controlled the roller because we had problems receiving the timing belt that was originally ordered a week before thanksgiving break and never arrived.  The roller used bristles that were generously donated to us by Memtech of Plymouth and were mounted to our PVC pipe and axle.