FRC 2020
Infinite Recharge
Our Robot
CAD Render
Although it might not look as pretty as our 2019 robot, our 2020 robot was easily the most complex robot the team had assembled at the time. Being so, we didn’t have enough time to put together a second competition bot from scratch before our first and last competition (due to Covid-19) unlike previous years. This complexity came from a combination of extreme height constraints due to the play style we decided to pursue at the beginning of the season, the natural complexity of the game, and the integration of a swerve drive and resulting lack of available motors and actuators that come with running a swerve drive (twice as many motors as tank drive).
The robot we brought to competition
Competition
We competed at the Arkansas Regional finishing as Quarterfinalists and winning the Chairman’s Award, qualifying us for the World Championship. Unfortunately the COVID-19 pandemic caused our second regional and the World Championship to be canceled, resulting in our 2020 robot only being able to officially compete once.
Strategy and Approach
We decided to make a cycle robot. As seen in the match footage, we spent the majority of the time crossing the field and scoring points. This meant we wanted to fit under the control panel and be able to quickly cross the center of the field.
This meant making a fast, short, and aggressive scoring bot that could maneuver around defense and score reliably from a wide range of positions on the field.
Drivetrain
Although a great debate was had over whether speed (tank) or maneuverability (swerve) was more valuable, we settled on swerve as the game was well suited for our new pneumatic swerve. Where many other teams with swerve drives struggled going through the center of the field due to the steel bars surrounding it, we could drive at full speed (16 ft/s) through the center of the field which distinguished and elevated our ability to cycle above other swerve teams. This capability can be clearly seen in our competition footage and our pneumatic swerve continues to attract the attention of other well known and distinguished swerve teams. Shown is a quick video of our 2020 robot showing off its maneuverability despite weighting over 150 pounds.
Power Cell Indexing and Climber
One of my major contributions was designing and manufacturing our indexing system. The hopper is a light construction of .04” aluminum square tubing and 1/16” thick polycarbonate sheet with pneumatically actuated bottom panels to act as agitators and prevent jamming. The “V-belt” is driven by a planetary gearbox with a custom reversing gearbox. 90 degree off the shelf drill adapters converted to a 1/2” hex shaft drive 36t HTD 5mm pulleys with belts that run the length of the robot. This tilted belt orientation ensures that once the balls fall onto the belt they will not catch on other balls or the edges of the hopper and tower. The tower is driven by a custom gearbox near the bottom of the robot and accelerates the power cells into the shooter at a consistent position. The gearbox that runs the tower has an integrated PTO that re-routes power through another separate planetary gearbox before being transmitted to two large aluminum spools that pull the robot up when climbing. This allows all power cell handling and climbing to be driven by just two motors and some pneumatics. The climber itself is made of a series of passively deploying plastic tubes with aluminum hooks pulled by dyneema rope from the spools. The flexibility of the plastic tubes and design of the hooks allowed the weight of the robot to be supported by the dyneema rope which enabled us to successfully climb on one hook on multiple occasions, one of which is shown in the video above.
Shooter and Rapid Iteration
At the time this shooter was the most complex and challenging thing I had designed and manufactured. Our shooter went through 7 iterations and 3 completely different configurations. Many of these iterations were minimum viable prototypes (MVPs) made from stacked 1/8” Masonite on a laser cutter we had access to. These prototypes were made to be fully function for only as long as needed in order to learn and inform specific changes to the design.
This design featured a two position pneumatically actuated hood that changed the release angle to shoot either close or far with smaller variations in distance being compensated for with wheel speed. The hood is made of two rails that slide past each other which helped center the balls and increase exit velocity due to the rails having very little friction on the balls. Despite all of this our shooter did not perform as well in competition as it did in practice due to the fact I did not take into consideration the varying compression rate of balls as they were destroyed by robots during the competition. Furthermore, due to competitions being canceled, I would not get the opportunity to address these oversights until the 2021 offseason.
The complexity of this design comes primarily from the many layers of interdependent design constraints. The shooter had to be strong and rigid to be safe while spinning at high speeds, yet light as it was the highest point of the robot, while still having enough weight and inertia in the wheel to not slow down between subsequent shots. From a modeling perspective the slider meant the maximum angle of the shooter was constrained by the minimum angle of the shooter. This meant the range of distances from which we could shoot changed such that our maximum range increased exponentially as our minimum shooting range increased linearly making finding a sweet spot difficult.