Answered: Trapping by robot falling on top of another robot

I was the Head Ref at a competition this weekend. During the first match of one of the semifinals, two robots with a U shaped chassis open in the front were in a shoving match, with both of their pick-up mechanisms lifted up far enough so that one wheel of the each of opposing robots was within the opening of the other robot. The blue robot started to back away, and the red robot, which had its lift mechanism up high, tipped over forward and landed squarely on top of the blue robot, pinning it to the ground. The red robot’s lift mechanism covered the entire blue robot - the base of the red robot was touching the floor in front of the blue robot, and the pick-up mechanism of the red robot was touching the floor in back of the blue robot. There was no way for the red robot to right itself, nor was there any way for the blue robot to get away. The match continued on briefly with the remaining two non-disabled robots.

At the conclusion of the match, I conferred with the two referees on what ruling, if any, we should make (all three of us were watching the match). This was our conclusion and the definitions and rules that guided our decision:

<G11> Strategies aimed solely at the destruction, damage, tipping over, or Entanglement of Robots are not part of the ethos of the VEX Robotics Competition and are not allowed. However, VEX Sack Attack is an interactive game. Some incidental tipping, Entanglement, and damage may occur as a part of normal game play. If the tipping, Entanglement, or damage is ruled to be intentional or egregious, the offending
team may be disqualified from that Match.

When the blue robot was backing away, it was possible that some entanglement had occurred, and as the blue robot backed up, it could have snagged the red robot, causing it to flip. Even if that were case, there was no intent to entangle, and we couldn’t call blue for entanglement.

An alternative possibility would be that the red robot’s extremely high center of gravity, combined with it trying vigorously to drive forward pushing the blue robot back, caused the red robot to tip over once the counterforce from the blue robot’s pushing was removed. Again, no intent on the part of the blue robot to tip – it just happened.

Pinning – A Robot is considered to be Pinning an opposing Robot if it is inhibiting the movement of an opponent Robot while the opposing Robot is in contact with the foam playing surface and another Field Element.

Trapping – A Robot is considered to be trapped if an opposing Robot has restricted it into a small, confined area of the field, approximately the size of one foam field tile or less, and has not provided an avenue for escape.

<SG3> A Robot cannot Pin or Trap an opposing Robot for more than five seconds during the Driver Controlled Period. A Pin or Trap is officially over once the Pinning team has moved away from the teams are separated by 2 feet (approximately one (1) foam tile). After ending a Pin or Trap, a team may not Pin
or Trap the same Robot again for a duration of 5 seconds. If a referee determines this rule to be violated, the offending Robot will be Disqualified for the match.

Once the red robot had landed on top of the blue robot, the blue robot had no way to get away, and the red robot had no way to try to pick itself up and back away from the blue robot. We couldn’t call the red robot for pinning, as the blue robot was not touching any of the field elements. However, since the red robot was literally on top of the blue robot (about an 18 inch square space), and the blue robot couldn’t possibly move, our conclusion was that the red robot (and therefore the alliance since it was during the playoffs) should be DQ’d for trapping. This resulted in the blue alliance being awarded the first game of the match.

I called over the four team captains, and explained our ruling, which three of the four understood – the dissenting team obviously was one of the teams on the DQ’d alliance, but not the robot that had flipped. Before I could announce to the audience the decision, the student on the dissenting team came up to protest that the red robot should not have been DQ’d as there were fewer than 5 seconds left in the match when the incident occurred, and you couldn’t be DQ’d for a pin/trap unless you held it for five seconds.

I reconvened with the referees and asked the RECF representative to join the discussion. It was apparent that the blue robot had absolutely no way to get out from underneath the red robot, and the red robot had absolutely no way to right itself to move away. There were a few seconds left on the clock, but none of us were absolutely sure of how much time was left afterwards. We agreed that the best “common sense” call was that in this situation, the blue robot was hopelessly trapped, and that even if there was a full minute on the clock, that couldn’t change. So we stood by our call of trapping and the DQ.

Does this sound like a proper call?



BTW, even after the DQ, the red alliance won the semifinal match 2-1.

This is correct. It is legal to Pin/Trap a robot for less than 5 seconds.

However, since you were not certain how much time was left in the match, this definitely comes down to a referees judgement call. I think your judgement was fine, but can definitely see how a different referee may have ruled differently.

Thank you for your detailed question and analysis, as well as for volunteering.

Thanks Karthik!

You’re welcome!

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