Many reports surfaced after week 1 events of teams using currently illegal retaining methods to secure their ropes to the davit. The prevailing method seemed to be crudely tieing their ropes/straps off to the davit fingers. This posed a safety/robustness issue, as was evident by the high number of robot drops and falls at various events.
Seeing as the rules allow for ropes significantly less than 1" diameter, the existing davit design is inadequate for securing off many legal ropes. It can be argued that teams should have considered this in their rope design, but I would direct your attention to example image 9-1.
The middle rope example shows a strap with loops at both ends, and no obvious knot/retaining feature larger than 1". Because of this, I believe many teams interpreted the rules to allow them to attach to the locking pin on the Davit. This method provides a much more positive, secure method for attaching ropes without actually affecting the intent of the rope rules. In no way does the retaining method at the top affect the performance of the rope below the touchpad.
Because of the poorly designed davit fingers, coupled with confusing rope retaining examples, 111 has asked in the Q&A (Question 652) for the GDC to consider exempting the section of rope around the retaining feature from section 9.D of the rules.
We used a separate locking pin (McMaster # 98416A019) for this example. This allows the field-provided pin to be easily removed without the weight of the robot being on that pin. One can then lift up on the second pin to remove their rope from the field.
We’re pretty much expecting the GDC to return with an answer that they can’t comment on possible teams designs, but we figured it was a question that needed to be asked.
That’s why their question includes a proposal to exempt that part of the rope from the rules. More likely, they’ll tell them to email some other person and ignore them.
I too agree that the davit fingers are a poor attachment point for teams using smaller ropes. Despite this, there are several valid and secure ways to do it within the current rules (and many threads discussing methods). I would suggest checking out Q142 and Q479 for some ideas.
Ever since they allowed the stopper knot to extend 2" below the davit fingers in Team Update 5 this problem has gotten a lot easier.
We submitted this because this is the ONLY system I’ve seen that doesn’t involve wrapping straps multiple times around sheet metal edges or tieing it off to a point of the davit clearly not originally intended to be used for securing a rope. If the horizontal -> vertical edge is wearing through ropes, I can’t imagine the davit fingers are any better.
The Q&A is phrased as a requested rule change for a reason.
E. be configured such that it engages securely with the FIELD with a Retaining Feature (RF) that does not extend more than 2 in. (~5 cm) below the DAVIT fingers.
This does not specify that it has to be a single large knot, just that it has to engage securely with the field.
We cannot rule absolutely on hypothetical ROBOT or ROPE designs, and the final decision as to legality of a particular ROBOT or ROPE lies with the Lead ROBOT Inspector (LRI) at each event. **Generally, loops which wrap around the DAVIT fingers would constitute engaging “securely with the FIELD” per I04-E provided that the ROPE still passes between the fingers (secured by the pin) to ensure that it does not slip off the fingers.
**
Please note that placing any knot used to form loops, as described above, that extends more than 2 in. below the DAVIT fingers violates I04-F.
Q342 Retaining Feature
If a loop spliced in the end of the rope engages securely with the field by looping around one of the davit fingers, per Q142, does part of it need to be greater than one inch in diameter? Since the splice is not a knot, per Q57, and the splice itself meets the specifications of a rope, is it ok that part of the splice extends more than 2” below the davit fingers?
Answer
No, provided it engages securely with the FIELD, there is no requirement that a retaining feature be greater than 1 in. in diameter. Yes, per I04, part E as updated in Team Update 05 any retaining feature may extend up to 2 in. below the DAVIT fingers.
However, while one DAVIT finger is capable of supporting the weight of a ROBOT, it does not mean that a ROBOT is incapable of applying enough force to damage the DAVIT finger. A team that damages a DAVIT finger will be in violation of G15.
In this case, the loading is on both DAVIT fingers, and is at the same point and in the same direction as would be achieved by the “poorly modeled knot” in the 1" line shown in the rules. Because the initial loop is under the running part of the loop which is under the pin, it is also unable to “flip up” under tension so that it is loaded onto the pin rather than the fingers.
I guess the confusing part is the blue box that accompanies that rule.
I04 part E blue box:
To interface with the field a ROPE must have a retaining feature (e.g. a
knot) greater than 1 in. (~25.4 mm) in diameter to interface with the
DAVITS (RF).
To interface with the field a ROPE must have a retaining feature (e.g. a
knot) greater than 1 in. (~25.4 mm) in diameter to interface with the
DAVITS (RF).
Also, as the davit fingers are 1" apart, a loop that wraps around both of them has to be greater than 1" across.
It’s worth keeping in mind the note on page 10 in the introduction section:
Warnings, cautions and notes appear in blue boxes. Pay close attention
to their contents as they’re intended to provide insight into the reasoning
behind a rule, helpful information on understanding or interpreting a rule,
and/or possible “best practices” for use when implementing systems
affected by a rule.
While blue boxes are part of the manual, they do not carry the weight of
the actual rule (if there is an inadvertent conflict between a rule and its
blue box, the rule supersedes the language in the blue box).
I agree with your assessment and think it is the best method. However, I did the exact same thing with a rope instead of a strap and it was deemed illegal.
Local events have a final say. I’m going back to this technique at Rocket City and hopefully will be successful this time. Be prepared with alternatives.
To the OP: I like your approach as well. GDC would have to change the rules to make it legal though.