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Courtesy of FRC Team 4817: One Degree North
This is yet another iteration of a competition bot for Infinite Recharge by Team 4817. The robot was designed to maximise ranking points. As such, in addition to the basic functionality of intaking, indexing and shooting, the robot includes a climber and a control panel manipulator to score bonus points.
2 sets of pneumatics are used to control the overbumper intake. At game start, the larger pneumatic extends the intake over the bumper, while a smaller pneumatic angles the roller to the ideal position to intake balls. A full description of this process can be found in subchapter 3.2 of Macro Design: Preparing for the Game Drop. Use the link for 3D Render on the right to get an overview of the robot.
After intaking via belts, the ball gets dropped into a rotating indexer. Using 2 sets of belts on an angled surface, the balls are kept in a circular motion to prevent jamming. The direction of the right belts are reversed momentarily when a ball is ready to be launched. Filtering for the flywheel is thus achieved. A full discussion or rotating indexers is included in subchapter 4.4 in the book.
Once a ball enters the double vertical flywheel, it is launched by 2 sets of wheels. The limelight positioned at the top of the mechanism helps with more precise shooting of the balls by varying the rotation speed of the flywheels. Learn more about how shot trajectories can be varied in chapter 5 of the book.
For the end climb, pneumatics are used to turn a pivot arm that is fitted with a single stage lift. Once the static claw latches onto the hang bar, the single stage lift is retracted.
Unfortunately due to COVID-19, this robot never saw competition. It was in the process of being built when it became clear that the team would not be competing. Aspects of the design were tested, but not to the point where all potential problems would have been identified. That being said, here are the learnings for this robot.
This was the second year in the team's history to attempt to CAD a complete robot. Designing a full fledged robot in itself is something to be proud of. CAD front ends the planning process and can be done even when the lab is not available.
The robot was designed with a tight budget in mind. So while alternative choices would have been made had the budget been more generous, the team was happy with the final design.
The rotating indexer was uniquely designed and worked surprisingly well. It was easy to build and used less parts.
To get around a limitation on the number of motors, 4817 for the first time successfully used gear shifting to allow for the same gearbox to power both the robot's drive base and climber. The process of gear shifting is further described in subchapter 11.4 in the book.
The climber worked most of the time, but due to the unpredictable nature of how rope spools around the winches, sometimes the climber would end up straining the rope. Adding slack in the rope allowed the climber to get around this problem, but this introduced a new problem. A better solution is to add springs at the end of the rope as explained in subchapter 8.2 of the book.
The brake utilized to hold the climber in place was easily susceptible to wear and tear. Using layered Delrin plates to mesh with the gear's teeth to act as a brake was possibly the best solution the team had available at the time, but using friction brakes to lock the axles would have been more effective.
In general the robot made heavy usage of pneumatics. Pneumatics were found to constantly leak and this became a never ending problem for electrical. Unless pneumatics got mastered by the electrical subteam in an off season, it was agreed that pneumatics be avoided in future robot designs.
Compare this design against 2 simpler versions in Ref 1 and Ref 17. Another top of the class solution can be found at Ref 20.
* Further explanation of mechanisms in FRC Handbook Volume 1 - Macro Design: Preparing for the Game Drop