Rules for hanging, using a loop over the end of the bar

[caffel]

Our machine cannot climb, but can easily reach the top of the bar from the floor.
We've been having a hard time hooking on (from about a 45 degree angle).
We saw a machine at PARC with a simple loop of cable which they intended to hook over the end of the bar from the outside, then hoist the machine up.
I've read the rules and this seems legal, but some teams (having not thought of it themselves) thought that it would be disallowed.
Did anyone see a loop (hoop?) succesfully used as a hook at a regional or the Nats?

Thanks,
Charlie Affel, mentor, 487

[Erin Rapacki]

Over the course of the FIRST competition, refferees have had different viewpoints on this issue. Some call a robot that is touching that corner bracket (that attatches the vertical bar to the horizontal bar) as NOT HANGING. Other refs say that if a robot is brushing up against it, thats fine. However (and here's where things get tricky), the intent of the rule is that... in the instance the vertical bar & bracket were removed, would the robot still be hanging?? That's where your robot comes in.

If you think about the force vectors involved, if your robot is hanging outside the vertical post and you have a loop around the corner-bracket... part of that loop is exerting force horizontally on that bracket. If the bracket were removed (depending on the angle), you're robot may fall.

I was the Head-Ref at PARC... as I recall this situation didn't come up. But if it did, I would be getting the graphing calculator out

ByE

erin

[OneAngryDaisy]

I'm guessing you would be talking about Buzz (175)- I spoke with them, as we were paired with them, and their driver said that they hung several times at Nationals but the hang was only counted once because the referees said it was touching the endpiece of the pole- hope that helps..

[caffel]

Thanks.
It would seem that any hook coming in from the side will have the same possible disadvantage (sliding to the end and touching the end fitting).
In any case, a strategy which requires debating force vectors with the ref isn't appealing.
Charlie

[Astronouth7303]

Originally Posted by Erin Rapacki

... However (and here's where things get tricky), the intent of the rule is that... in the instance the vertical bar & bracket were removed, would the robot still be hanging?? That's where your robot comes in.
...

If I take this as the law, then a noose would NOT count. however, a hook may count, depending on exact cirumstances.

[dlavery]

Originally Posted by caffel

In any case, a strategy which requires debating force vectors with the ref isn't appealing.

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

[sanddrag]

At the driver's meeting at the Phoenix regional they said that not only if it is touching at the end of the match, but if it touches while pulling up, even if it then slid away after getting up, it would not receive points. However, this was not always enforced.

[Steve W]

Originally Posted by dlavery

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.

- 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

Dave , I don't usually disagree with you but the hanging rule has been in my craw since the 2nd week of competitions. First of all the Q&A's were not rules. They also changed from day to day and after a while we stopped reading them as they became repetitive. If you read the rule about hanging it was stated that hanging was being support by the horizontal bar and not touching the platform, goals or floor. There is nothing about the touching the vertical pole (the pole was stated as not being part of the platform) or the mounting at the top. You are not allowed to hold onto the vertical bar or be on the mounting on the top. Teams built their robots following this guideline. I believe that there was even a Q&A that asked if you could be touching the side of the mount and /or the vertical pole. There was an OK (Not official but not denied in any official rules either)

FIRST said that they were trying to be less legalistic this year but became overly legalistic on this issue. If you removed the mounting AND vertical pole then the horizontal pole would lower. This would cause all robots to slide off or touch the ground. If this were the case why did any robots get classified as hanging? The other issue was that this problem was started by legalistic referees who started to influence how the game was played. If they had called by the rules the whole season there would have been a lot less problems. FIRST made a huge mistake by changing the rules week by week and the refs interpreted different at each regional. I have ranted enough in other forums on this issue and will bring up at the feedback sessions. There were other issues that were touchy and questionable that FIRST made a direct statement on and will probably review in the off season. That is the way hanging should have been dealt with. There is no place in the rules to support any of your interpretations that I could find so I believe that we should be looking at the rules and following them.

For background, our team hung from the outside but swung around over the platform if unimpeded by another robot. Our hook only touched the side of the mounting if we were being pushed it the time of rising. We designed our hanger according to the rules that were posted and realized that if we touched the platform at the end of the game it would not count. However there was no rule stating that your robot had to be higher than the 12" platform. This means if you were 2" off the ground, resting against the vertical pole (which is legal) and not touch the platform, goal or floor then you were legally hanging. During competitions this was not counted as they came in with the move the robot, pole, mounting rule that would then cause your robot to touch the side of the platform. How much easier would it have been to state that your robot must be greater than 12" from the ground to be considered hanging?

One last note. One thing that I have learned when working with teenagers (some are in their 60's) is that they need and want firm rules. They don't want wishy-washy rules that change from day to day. People want to know where they stand. I will end with this last question - How fast would you drive if the speed posted said 60 MPH? (hard to put 2 ?side by side)?

[dez250]

Page 2 of section 4, the Game.

HANGING – A ROBOT is considered HANGING from the Pull-Up Bar if it is directly SUPPORTED by the horizontal bar and is not touching the carpet, platforms, or goals.

[edit] So i have gotten many questions on what i meant when i posted this reply and i guess i should explain it now. What i was trying to show is exactly what is in the rule book for FIRST on this problem. I am not taking sides with one person or another, i understand where everything is coming from but as i have been told by Bengie and understand is if the only thing left is the hanging bot and the horizontal bar, and the bot would still be hanging completly then it gets the 50 pts. But in the final call its all up to the REFS!!! [/edit]

[scottconnery]

Just want to throw my 2 cents in here. Our bot (126) also hangs from the floor over the end caps of the bar. The difference is that we designed a lexan cross piece to use in the actual pull up (not a wire loop). So our pull is directly down, not down and out; ie. no sliding across the bar. If you were to remove the end bar, our bot would swing under the pull up bar and continue to hang in almost every case. Luckily we never had any troubles with the refs on this and were awarded points every time we remained above the platform.

[Twitch]

Originally Posted by dlavery

- 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.

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.

Don't these two statements clash? If a robot is hanging from the ground, it must be exerting some lateral force since the bar is not directly above it. It is possible to counter this force with friction so that the gripping device will not slide across the bar and come in contact with the vertical bar or couplings. However, if we assume the bar is a fricitonless surface, the robot will slide across it regardless.