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Originally Posted by caffel
In any case, a strategy which requires debating force vectors with the ref isn't appealing.
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Exactly. If I recall correctly, this was actually addressed during the season - I am pretty sure there was a Q&A about it (if I remember, I will look it up later). Anyway, here was the basic approach that was described by FIRST, and passed along to all the head refs during their weekly telecons:
- the intent behind the hanging rule is that a robot is hanging if 100% of the force applied to the Chin-up Bar is in the vertical direction. No horizontal force vector should be applied to the vertical support post or the pipe fittings at the end of the Chin-up Bar.
- robots that attach to the vertical post or pipe fittings are not considered hanging.
- in other words, a robot is only considered hanging if it would still be hanging from the Chin-up Bar if the vertical posts and fittings were not present.
- if a robot is completely inside the vertical posts, and cleanly hanging from the Chin-up Bar, then incidental contact with the fittings is OK.
- to avoid having the referees calculate coefficients of friction in real time to determine if a robot would stay on the bar or not, we assume that the Chin-up Bar has a frictionless surface. Therefore, if the robot is applying any horizontal force at all to the fittings or the vertical posts, we assume that if the fittings or posts were not present then the robot would slide off the end of the Chin-up Bar.
- under that determination, if a robot is hanging while outside the vertical posts (i.e. the robot has grabbed the Chin-up Bar but is hanging while leaning against the outside of the vertical post), then the following considerations apply:
A - if the attachment device (grapple hook, gripper or whatever) is just in contact with the horizontal Chin-up Bar (and does not touch the fittings or vertical post), then it is assumed that if the vertical post and fittings were removed then the robot would freely swing "inside" and under the Chin-up Bar, and would be cleanly hanging under the standard definition.
B - if the attachment device is contacting the fittings or vertical post, then it is assumed that it is applying horizontal force to those items, and if they were not present the attachment device would slide off the end of the Chin-up Bar and the robot would fall to the ground.
(note: I am paraphrasing here for the sake of brevity. The exact wording may not fully match the FIRST definitions, but hopefully the basic approach is adequately communicated)
Thus, a team that designs a robot to hang from the bar while "outside" the vertical posts needs to take great care to be sure that the attachment device does not contact the fittings or vertical post. With that in mind, back to the original question. Formally, a lasso-type device is allowed by the rules (i.e. there is nothing that says you can't have one). However, such a device would likely run the danger of being in contact with the fittings, and thus lead to a determination that the robot would not be hanging. So while you can build one, it is not at all clear that you can do anything useful with it.
-dave