Making FM-87: Field Elements 2020 Season
Constructing all field elements in the game would have been technically possible, but since we have limited personnel and time, we wanted to work smarter, not harder. Our initial strategy only called for interacting with/working around the following field elements: the Bottom Port, Control Panel, Trench, and Shield Generator. Note that we didn't end up needing the Shield Generator due to time/resource constraints, but all the field elements were completed before making this decision.
The most difficult part (other than materials issues, detailed later) of constructing the Control Panel was cutting a perfect circle. To do this, we rigged up a makeshift compass, pinning one end of a yardstick to the center of the Panel with a drillbit and attaching a boxcutter to the other end. We used this "compass" to score a perfectly circular cut in our plywood. We followed this path with a jigsaw, which naturally fell into the groove. Finally, we ground off the sides to leave a smooth, splinter-free edge.
Our build space already had a table that was just 5/4" shorter than needed for the trench. We raised it up on 1" wooden blocks and called it a day.
Due to materials constraints (see Challenges and Workarounds), we had to modify the design of the Shield Generator Structure. This included lowering the height of the supporting crosspieces, which created some difficulties in installing the mounting points for the Shield Generator bar.
We also had to decrease the length of the Shield Generator bar, which required repositioning the supports on either end; otherwise, the bar would not have been at the correct angles. We used some quick geometry (see, you do use trigonometry outside of school!)
SAFETY WARNING: We are adults with experience in engineering and construction. This is the only reason we felt comfortable altering the plans of this load-bearing structure. If we had made a mistake, hanging a robot off it could have been gravely dangerous. Please have a mentor experienced in structural engineering and/or construction help you build any structure designed to support your robot, and if you need to alter the official FRC plans for any reason please ask them to do so. Remember, your structure should be able to support twice the expected load to account for any construction errors; in this case, our structure can theoretically support over 300lb.
The Bottom Port construction suffered the most from materials shortages, to the extent that the official instructions for this element had to be ignored in favor of our own design. We opted to create our support from simple, heavy backstops supporting a flat board with a jigsaw-cut hole.
Challenges and Workarounds
While the structure of the Control Panel was fairly simple to manufacture, we ran into a a materials problem. We needed two 4'x4' sheets of plywood to create the top and bottom of the panel, and we needed wooden dowels to create the spacers between the two sheets. However, once we had sourced all the plywood we could find (scrap from NC State campus's maker spaces), we only had one piece of plywood big enough to cut the whole circle. To accommodate for this, we simply created the top of the Panel from two pieces of wood, each forming half the circle. To replicate the dowels, we used some scrap wood of the right size and used a grinder to form the robot-facing edge into a semicircle, so that if our robot needed to interact with the supports we would have an accurate approximation.
We faced a similar challenge building the shield generator structure; even after searching for all the spare 2x4 planks we could, there was still not enough material available to accurately imitate the plans for the structure. This forced us to shrink the width of the structure and lower the supporting crosspieces (both solutions that shrunk the total length of wood being used).
The Bottom Port was the last element to be constructed since it was the simplest (after the Trench); it bears no weight and doesn't need to move. Because of this low priority, however, our resources were extremely depleted when we finally got around to it. We ended up with not quite enough wood to reach the bottom of the playing field, but we knew our robot didn't fit beneath the gap so that should be OK. We were very lucky our strategy team had decided against shooting into the Inner/Outer Ports, since we would have needed to find a lot more wood.
The field elements are a vital part of the robot creation process (you never know if something works until you've tested it), however it is important not to over-commit resources. Due to our time and personnel constraints, much like those faced by most FRC reams, we wanted to produce minimal but functional field pieces. That's why we only built the elements we absolutely needed, and we utilized the resources around us to use stand-ins for easy-to-replicate elements. We also had to think outside the box to accommodate for a lack of materials, so we prioritized keeping everything that the robot would interact with true to field, while internal/secondary structure pieces could sacrifice some accuracy.
Text Media Team Member