For nearly a quarter century, RoboCup has pursued an ambitious goal: by 2050, a team of autonomous humanoid robots should defeat the reigning FIFA World Champion. Alongside the main leagues, RoboCupJunior engages high school students in three categories—Soccer, Rescue, and OnStage—providing a scaled challenge to nurture future roboticists. Traditionally, the Soccer category requires teams to design, build, and program physical robots to play soccer. When the COVID-19 pandemic disrupted in-person events in 2020 and 2021, organizers sought a way to preserve competition spirit without physical gatherings.
Inspired by prior simulation successes in senior RoboCup leagues, the RoboCupJunior Soccer Technical Committee developed SoccerSim, a 3D simulation environment based on the open-source Webots robotics simulator. Existing simulators often targeted university-level research, making them complex for younger students. SoccerSim aimed to be visually engaging, easy to set up, and open-source, with Python as the primary programming language due to its accessibility and growing popularity.
Webots, maintained by Cyberbotics Ltd. since 1998, offers an integrated development environment compatible with Linux, macOS, and Windows. It includes a library of robots, sensors, actuators, and materials, and supports multiple programming languages. SoccerSim leveraged Webots’ physics engine and supervisor functionality to implement an automatic referee that enforces adapted RoboCupJunior Soccer rules. Matches feature two teams of three differential-drive robots competing for 20 minutes, with rule modifications such as automated ball resets for “lack of progress” and penalties for excessive goal-area camping.
The development process included a February 2021 demo competition to test the beta version. Over 50 teams from 18 countries registered, with 41 submitting code. This early trial revealed organizational challenges—none of the submissions matched the required format for automated tournament tooling. In response, developers created a submission checker and SoccerSim Checker, a web application that simulates short matches to verify code behavior before official submission.
Student participation proved critical. Forum discussions after the demo surfaced bugs such as duplicate code assignments to robots, false goal detections, and unsynchronized match timing when simulations were sped up. These were corrected before the official RoboCup Worldwide 2021 event.
The June 2021 competition integrated SoccerSim into a broader virtual environment hosted on GatherTown, which provided an interactive, avatar-based meeting space for six days of activities—poster sessions, interviews, and spontaneous discussions. Time zone differences were managed by scheduling daily updates at 15:00 UTC. The SoccerSim tournament included individual and “SuperTeam” competitions, where teams from different countries collaborated on joint submissions. Technical challenges tested specialized skills: rapid goal scoring, ball passing within fixed zones, and precision shooting using simulated Lidar sensors.
Matches were recorded using Webots’ video API, with HTML5 playback enriched by clickable event timestamps for goals, rule infractions, and match milestones. Some quarterfinals and finals were live-streamed with commentary, drawing strong engagement. Feedback indicated that expanding live coverage and improving remote collaboration in SuperTeam events would enhance future competitions.
Participation data showed that simulation attracted more teams than 2020’s virtual poster session, despite being a paid event. The lower hardware barrier—requiring only a computer—enabled involvement from regions without established RoboCupJunior communities. Survey responses reflected high satisfaction: an average enjoyment score of 8.11/10 and 80% of SoccerSim participants expressing willingness to compete again.
Ongoing development focuses on increasing realism by adding sensors like infrared ball emitters, GPS, compass, and ultrasonic detectors, all with simulated noise. Continuous integration pipelines enforce code quality and unit test coverage for the referee logic. Future enhancements may include camera-based vision systems and customizable robot designs, broadening the challenge beyond programming to mechanical design.
The long-term vision is a fully automated tournament system—from submission intake to match simulation and results publishing—enabling frequent “SoccerSim leagues” throughout the year. By combining accessible tools, open-source collaboration, and community-driven refinement, SoccerSim demonstrates how a well-crafted simulation can sustain and even expand educational robotics engagement under constraints that preclude physical competition.