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  #16   Spotlight this post!  
Unread 13-01-2017, 16:49
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Re: Thin rope!

Quote:
Originally Posted by jnicho15 View Post
One of these things is not like the other...
If you can figure out the knot, I think you can also figure out unit conversion.
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Unread 13-01-2017, 17:27
Ian H. Ian H. is offline
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Re: Thin rope!

I was under the assumption that the retaining feature could be a loop and/or knot. Because the davit has 2 steel fingers, with the manual saying:

These fingers are 1¼ in. (~3 cm) apart and
have a hole for a locking pin. The ROPE passes through the fingers with the top knot on the AIRSHIP
side of the fingers.

This phrasing implies that there has to be a knot, because the top knot is on the AIRSHIP side of the fingers, but part of me thinks this only is referring to the rope installed on the field. But the definition of ROPE, seems to imply otherwise.

However, the black rope in the picture in IO4 has 2 loops:



and IO4 E says:

E. be configured such that it engages securely with the FIELD.
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).


This seems to say something other than a knot is allowed.

There seems to be contradicting info, but if a loop is allowed it seems like you could just put a loop around one of the steel fingers on the davit and it would still pass through the fingers
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Last edited by Ian H. : 13-01-2017 at 17:29. Reason: Now image should show up
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Unread 13-01-2017, 17:42
chrisrin chrisrin is offline
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Re: Thin rope!

Frankly, from a safety standpoint, I'm surprised a 100% safe method for securing the rope at the top isn't being required. If a team uses a thin rope with a knot they presume is thick enough but isn't under certain scenarios (e.g. hanging robot actually bumped by another robot), then the hanging robot could fall to the ground with the current guidelines. A worse scenario would be the robot falling on a person because the top knot slipped through the 1" opening after the match when students are trying to extract their robot. There are many types of rope/cord out there with different characteristics. It would have been far safer IMO to include in the KoP a 100% reliable plastic anchor compatible with any (within reason) type of rope OR to require a loop at the top and usage of the fingers mentioned in the previous post.
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Unread 13-01-2017, 17:49
KevinG KevinG is offline
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Re: Thin rope!

Quote:
Originally Posted by chrisrin View Post
Frankly, from a safety standpoint, I'm surprised a 100% safe method for securing the rope at the top isn't being required. If a team uses a thin rope with a knot they presume is thick enough but isn't under certain scenarios (e.g. hanging robot actually bumped by another robot), then the hanging robot could fall to the ground with the current guidelines. A worse scenario would be the robot falling on a person because the top knot slipped through the 1" opening after the match when students are trying to extract their robot. There are many types of rope/cord out there with different characteristics. It would have been far safer IMO to include in the KoP a 100% reliable plastic anchor compatible with any (within reason) type of rope OR to require a loop at the top and usage of the fingers mentioned in the previous post.
Stuff like this is going to fall on the RI to approve. Presumably the RI would notice that the knot is not sufficiently robust and would instruct the team to correct it. Given the safety issue I suspect this will become a point of emphasis. FIRST has already provided a safe method of securing the rope to the field, and it seems fairly robust and simple too. Most people should be able to knot a rope to a minimum of 1" width.

Personally I'm surprised that the GDC hasn't implemented a minimum width for this exact reason. Maximum 1", minimum 0.5", for example.
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