Humanoid Sumo — Official Rules

1. Definition of the Sumo Match

A match is fought between two teams, each with one or more members. Only two members from each team may approach the ring: the operator and the assistant; the others watch from the audience. Under these rules, each team competes on a Dohyo (sumo ring) with a self-built robot that satisfies Section 2.

The match starts at the judge’s command. The judge determines the winner. After the match, the operator and assistant return to the designated rooms and wait for the next game.

2. Requirements for Robots

2.1 General Specifications

• Any design allowed unless limited by Section 2.2.
• Must fit within a 200 × 200 mm square; maximum height 500 mm.
• Total mass < 3 kg (3000 g) at match start.
• Must be a two-legged walking humanoid biped that shifts its center of gravity to maintain balance while walking.
• Fully autonomous; all control onboard; no external interaction.
• Visible competition number (provided by organizers) on the outer shell.

2.2 Restrictions & Walking Criteria

• During walking, one foot must lift from the floor while the other balances the robot.
• Balancing leg’s knee joint must have an angle > 90° while walking; otherwise it is not considered walking.
• Feet:
  • Foot = the part contacting the arena surface.
  • Max foot length < 50% of extended leg length (ground contact to hip axis).
  • Max absolute foot length < 200 mm.
  • When standing/walking, rectangular outlines around left and right feet must not overlap.
• Must have two arms (each arm’s extended length ≤ extended leg length) and a head.
• No IR jamming; no damaging parts; no liquids, powders, gases, flames, or projectiles.
• No sticky traction substances.
• Start behavior: robot must stand still for 5 seconds before moving once the match is started.
• Start methods: remote or local button on robot. Prohibited: start via laptop with a connected cable.

3. Dohyo (Sumo Ring)

3.1 Interior

The dohyo interior is the playing surface including the border line; outside it is the dohyo exterior.

3.2 Specifications

• Ring: circular, steel 5 mm thick, painted black, diameter 1540 mm.
• Border line: white circular ring, width 50 mm.
• Platform height: 50 mm wooden base.
• Tolerance on dimensions: ±5%.
• Starting lines (Shikiri-Sen): 200 × 20 mm.

3.3 Exterior

A suitable space (“ring area”) surrounds the ring; material and color at organizer discretion.

3.4 Match format on the ring

• One match: 3 rounds within 3 minutes unless extended by judges.
• First team to win two rounds or earn two Yuhkoh within the time limit wins. If time expires and one team has one Yuhkoh, that team wins.
• If no winner in time: extended match (first Yuhkoh), judges’ decision, lots, or rematch.
• Non-start or entanglement: see 6.1.
• If a hand-aimed repeater to a start sensor is used and the robot doesn’t start, no restart; responsibility lies with the team (tested twice before each round).

3.5 Course of the Competition

Important: One person may be operator for a maximum of 2 robots during the whole contest.

• Robots may be split into groups depending on participants. Format: groups → quarterfinals → semifinals → finals. Group matches best-of-3; finals may be best-of-5. Three referees (principal + two assistants). Decisions must be unanimous and are final; disputing can lead to disqualification.
• Same-team robots that meet must play; no arranged advancement or opponent selection.
• Group order randomized after opening; schedule posted on website and in team rooms. With too few participants, a pyramidal knockout is used with random positions.
• No breaks are allowed during a match. Between matches, changes, repairs, and re-programming are allowed.
• Teams remain in their assigned rooms and move only when called to the waiting area near the arena.
• Homologation is performed for robots about to start; they remain in the waiting area. Leaving is only by referee approval.
• Follow the schedule. PLEASE DON’T BE LATE — WE WILL NOT WAIT! If called and you don’t arrive within 5 minutes, the robot is disqualified.
• Exactly one operator and one assistant are allowed in the waiting/game area per team. Others watch from the audience.
• Protective eyewear and gloves are mandatory in the game area and checked at homologation. Missing gear may yield a Yuhkoh to the opponent or disqualification.
• Up to 1 minute between rounds for cleaning and configuration (without touching once placed).
• Robots may not be touched once placed until the judge instructs after the fight.

3.6 Homologation (Technical Inspection)

At event start

• Check visible competition number; take a photo with the number visible.
• Dimension check using a bottomless 203 × 203 mm frame.
• Weighing: ≤ 3005 g.
• Verify operation of the start/stop sensor (as applicable).

Before every match

• Dimension check with 203 × 203 mm frame.
• Weighing: ≤ 3005 g.
• Verify visible number and protective gear for operator and assistant.

After homologation, the first 4 teams stay near the arena; the rest return to their assigned rooms.

4. Start, Stop, Resume, End

4.1 Robot placing

• On judge instruction, both operators place robots simultaneously and retreat to the safe area.
• All parts must be behind the Shikiri-Sen; no part may cross toward the opponent.
• Placement must be within the vertical projections of both starting lines. Incorrect placement → re-position.

4.2 Start

The referee gives the start command. Operators start the robots, which must remain still for 5 seconds and then move. Start occurs only after operator/assistant are in the safe area. Leaving the safe area without approval may cost a point or cause disqualification.

4.3 Stop / Resume

The match stops/resumes only on a judge announcement, including placement, retreat, and recovery moments.

4.4 End

The match ends when the judge declares so. Teams recover robots. After recovery, the decision is final; no objections accepted.

5. Time of Match

• Duration: up to 4 minutes per match.
• Extension: if called by the judge, up to 1 minute.

6. Scoring

A. Knockdown

Robot is knocked down by the opponent → +2 points to opponent.

B. Slipdown

Robot falls on its own → +1 point to opponent.

C. Ringout

Any part of a robot contacts the surface outside the arena → +3 points to opponent.

With judge permission, the team may place its robot face-down inside the arena with no further penalty, provided it can stand within a 10-second count.

D. Knockout

Failing to get up within 10 seconds, or being unable to move/walk when commanded within 10 seconds → knockout. The match ends immediately and is awarded to the opponent.

E. Round points

All points are totaled for opponents each round.

F. Inactivity

The judge may stop the match if robots do not touch for > 15 seconds and no clear will to fight is observed.

G. Determining the winner

• The robot with the most points wins the match.
• Knockout immediately ends the match in favor of the opponent.
• Tie on final score → judge decision based on tactics, aggressiveness, and activity.
• If neither robot scored, the judge may declare no winner.

6.1 Stoppages & Rematches

• Non-start: one restart; if repeated, point to opponent.
• Entanglement/orbiting ~10 s with no progress: one restart. If repeated, winner is the robot that moves more and shows will to fight; if repeating again, the faster/more attacking robot wins the round.
• No progress / simultaneous stop 5 s without contact: evaluate. If one stopped first and 5 s pass, that robot is deemed lacking will to fight → opponent gains a Yuhkoh. Judge may extend up to 30 s to assess progress.
• Indistinguishable simultaneous ringout: rematch.

6.2 Repairs, Modifications, Interruptions

• If a robot breaks during a match, the main referee may allow up to 1 minute of repair (extendable to 5 minutes by organizers). Repairs are supervised to prevent unapproved module changes.
• If it cannot be repaired in time, the opponent wins the match. Repairs may continue (under supervision) until the next match.
• Defective parts replacement and battery recharge are allowed during the competition as needed.
• Any modification after homologation requires passing homologation again.

7. Violations

7.1 General

Any deeds described in Sections 2.2, 7.2, or 7.3 constitute a violation.

7.2 Insults

Insulting opponents or judges (spoken, audio, or written on robot) or any insulting action is a violation.

7.3 Protective Gear & Safe Area

Serious misconduct includes failing to retreat to the safe area or disobeying referee instructions.

7.4 Minor Violations (warnings)

• Entering the ring during the match (except as instructed after a Yuhkoh). Includes any body part or tools used to support the body.
• Requesting to stop without valid reason.
• Taking > 60 s to resume without judge’s extension.
• Actions contrary to fair play.
• Leaving the waiting area without informing officials/referee.

Accumulating 2 warnings awards one Yuhkoh to the opponent or may result in disqualification depending on severity.

8. Penalties

• Violations under 2.2, 7.2, 7.3 → match loss; opponent receives two Yuhkoh; violator must clear out.
• Minor violations under 7.4 accumulate; two warnings → one Yuhkoh to the opponent.
• If a robot starts before the 5-second delay, +1 point to the opponent.

9. Objections

• No objections against judges’ decisions.
• Rule-application doubts may be raised by the operator to the Committee before the match ends. If no Committee is present, raise to the judge before match end.

10. Flexibility of Rules

As long as core concepts are observed, organizers may modify or abolish rules provided changes are published prior to the event and applied consistently.

11. Liability

• Teams are responsible for their own safety and that of their robots and are liable for any accidents caused.
• The Relativity Robotics Challenge organization and staff are not responsible or liable for incidents/accidents caused by teams or their equipment.

Appendix 1 — Team’s Folder

• Numbers for each robot
• Participation diplomas
• Badges for team members
• Info about rooms and competition area map
• Promotional material
• Explanation of group formation
• Maps for team rooms and the competition areas