RADS Theoretical Ratio

[Reg]

[ QUOTE ]
I am sorry my friend, you are indeed correct. My bad.

For every one foot you go up there will be one foot flaked on the ground.

But are you honestly saying that you do not believe that the principles of 2:1 are not happening when a climber climbs on a fixed pulley.

Dave

[/ QUOTE ]

I'm not saying a dam thing else Dave

, just getting the hell out of here while I can. Back to the crane and rigging forums. Cheers

 

[Tom Dunlap]

[ QUOTE ]
It's all jet packs and fairy dust to me.

[/ QUOTE ]

this discussion has been going on for YEARS! Every arbo forum that I've read has a long and heated discussion about the MA of RADS.

I remember the first trees that I climbed using RADS with an I'd. After the second tree I could see the MA but it wasn't enough gain to overcome all of the rope that I would have to yard through the system to move up the rope. In the end I decided that I used more calories to move up. I displaced energy input in lifting into energy used to pull rope and push the system up ahead of me.

During my RADS trials I would use some frog walker type ascent system then change over to RADS to work the canopy on the way down.

To make RADS a bit more efficient this is the setup that I used. First, the upper.

 

[Tom Dunlap]

Lower.

By adjusting the length of the yellow cord the Shunt will release and slide down the rope with the climber. That keeps the Shunt/upper within arms reach for normal climbing. When doing limb walks it can be detached and left 'back there' to use as the redi when working back to the center of the tree.

Please accept my derail...but I figured that since RADS was in the spotlight I'd add in a bit of efficiency.

 

[DSMc]

[ QUOTE ]
this discussion has been going on for YEARS! Every arbo forum that I've read has a long and heated discussion about the MA of RADS...

[/ QUOTE ]

And that's a pretty sad statement.

We spend our entire careers working with complex biological organisms, always having to give cautious answers to questions due to endlessly variable conditions.
You would think that when presented with a problem as simple as RADS that can actually be definitely answered, we would jump at it.

Dave

 

[TLHamel]

RADS Discussion, part 3

RADS Discussion, part 4

RADS Discussion, part 5

Serious video rant. But, hey, whatcha gonna do? Broke it down to three shorter vids.

Here are the first two links in case anyone isn't bored to death, yet. The newer vids cover these points in better detail.

RADS Discussion, part 1

RADS Discussion, part 2

 

[treebing]

Ok, rads is 2:1. Ddrt by the same logic is 1:1. What would we call SRT?

 

[Ron]

[ QUOTE ]
Ok, rads is 2:1. Ddrt by the same logic is 1:1. What would we call SRT?

[/ QUOTE ]
I gather your statements should be taken to make a point rather than actually claiming the ratios to be factual?

RADS is a 2:1 to a ground referenced person; it is 3:1 to the climber. I can prove that by measuring pulling forces and by the distance pulled.

The ground referenced guy will pull half the weight twice as far as the weight moves. If the climber is the weight, he has to pull 1/3 his weight through a distance of three times the amount he rises.

 

[rangerdanger]

Agreed. I see how RADS is a 2:1 now. But, DdRT is still a 2:1 also, RADS is just a redirected 2:1, correct? So, by that logic, SRT is still the 1:1 system.

 

[Ron]

TLHamel,

You are seeing a 2:1 because you are ground referenced. You don't move off the ground at all, so you are ground referenced. The system is not supporting your weight at all. If the system had you fully suspended, there would be three lines supporting your weight, not two. When you pull yourself up you would only have to supply a force equal to 1/3 your weight.

When you are suspended and your full weight is on the system, you will move up one-third of the distance of the line you pull.

What's so deceptive about this is that the climber is moving up at the same time his hand moves down. It is very difficult to see that the arm(s) actually pulls 1/3 of the force through 3 times the distance.

Here's an indicator. Get a scale and measure the force in the pull rope of an all pulley RADS (eliminating friction) and see how much tension is in the pull line. It will be 1/3 your weight, not one half.

I argued the very same thing, i.e. the RADS is 2:1, the same way, did all the measurements, etc., but then two guys, one a physicst kept insisting the RADS was a 3:1 to the climber and a 2:1 to a ground referenced person. I finally realized the "work" won't balance out for a suspended climber as a 2:1, but it does as a 3:1.

And throughout my arguments, in the back of my mind, it was forever nagging me that in a RADS, when I pull myself up, there are three lines supporting my weight. I could not resolve how three lines supporting the load could produce a 2:1 ratio. Well, it couldn't. So I had to really study a pulley system where the pull line attached to the load and produces an extra support line. I finally saw the light thanks to a buddy and a physicst.

Here's a discussion of the 2:1 which I did as a preface to the RADS. It explains the very same concepts but with a simpler system.

http://www.youtube.com/watch?v=76l9KZ6XcME

I have the RADS version up, but it doesn't clearly show the distances that support the 3:1 ratio so I'm redoing it so it becomes clear the RADS (frictionless) is truely a 3:1 to the climber.

 

[Reg]

[ QUOTE ]
Ok, rads is 2:1. Ddrt by the same logic is 1:1. What would we call SRT?

[/ QUOTE ] A simple redi is a 1:1 also. Maybe dont refer to SRT in ratios at all Kevin....because the line remains static the whole time and doesn't actually involve pulling or moving anything, unlike all the other configurations mentioned.

 

[Ron]

Reg,

All due respect, but you have to be careful about how a redirect is connected to the load. If both strands come back to the load, i.e. the climber, as in a frictionless DdRT, each strand only experiences half the climber's weight. So if the climber has to hold himself in position, or lift himself, he only has to supply 1/2 his weight. I illustrate this clearly in the video I referenced above, repeated here for convenience, especially at the 5:00 mark:

http://www.youtube.com/watch?v=76l9KZ6XcME

Either what I'm saying is true and I only have to lift half my weight, 100 lbs, or I'm an incredibily strong guy and can lift my full 200+ lbs with one arm.

 

[Ron]

In fact, here's the RADS vid; I had it private, but now it's public:

http://www.youtube.com/watch?v=v1p-xuZNq5g

 

[Reg]

[ QUOTE ]
Reg,

All due respect, but you have to be careful about how a redirect is connected to the load. If both strands come back to the load, as in a frictionless DdRT, each strand only experiences half the climber's weight. So if the climber has to hold himself in position, or lift himself, he only has to supply 1/2 his weight. I illustrate this clearly in the video I referenced above, repeated here for convenience, especially at the 5:00 mark:

http://www.youtube.com/watch?v=76l9KZ6XcME

Either what I'm saying is true and I only have to lift half my weight, 100 lbs, or I'm an incredibily strong guy and can lift my full 200+ lbs with one arm.

[/ QUOTE ]

Ron I wasn't even refering to climbing, I daren't....just pulling a line with a weight on the other end, 1:1. My point (if you can call it that) was just how SRT differs in that the line is static throughout (unlike all the other configurations) so perhaps doesn't even warant being called a 1:1. I was simply replying to Kevin, not looking to go over old ground or into any depth whatsoever. Thanks, and I appreciate and enjoy all your videos, good work.

 

[Ron]

Hmmm, my bad Reg, looks like I 'read' stuff into your comment that wasn't there.

Seeing your clarification, I agree 100%.

And regarding the vids, thanks much for the kind words - that means a lot to me.

 

[DSMc]

Slam dunk, Ron. I don't know how it could made more clear but be prepared for the next round of "yeah, butts".

Dave

 

[Ron]

Thanks Dave.

The MA of the RADS is confusing - I know - as I stated previously, a few years back I adamately argued that the RADS was a 2:1 period, but the math just wouldn't support a RADS as 2:1 climber referenced, and then I saw the physical reason why.

I think I need to do a follow up vid showing the measured movements and forces, that may make it a little clearer why it's 2:1 one way and 3:1 another way and how it happens.

I think I mentioned this in one of the vids: it almost seems like magic.

 

[treebing]

I think as long as you keep everything consistent. Than you can call it what you wish. I find seeing Rads as a 3:1, ddrt as a 2:1 and SRT as 1:1 easy to work with. Otherwise you have to find a new vocabulary. Srt as merely static and ddrt as a redirected 1:1 is complicated because it doesn't Feel like a 1:1 just as rads doesn't FEEL like a 2:1. But it is fir to e things whatever you wish as long as you are cosistant with it.

 

[Ron]

[ QUOTE ]
I think as long as you keep everything consistent. Than you can call it what you wish. I find seeing Rads as a 3:1, ddrt as a 2:1 and SRT as 1:1 easy to work with. Otherwise you have to find a new vocabulary. Srt as merely static and ddrt as a redirected 1:1 is complicated because it doesn't Feel like a 1:1 just as rads doesn't FEEL like a 2:1. But it is fir to e things whatever you wish as long as you are cosistant with it.

[/ QUOTE ]

I understand what you're saying. But consistently calling something incorrectly won't make it correct. If I call black, pale white consistently, then I'd just be consistently incorrect.

However, the theoretical MA of a RADS system is not a 'shade of gray' nor 'tomahto/tomato', it's black and white. It's either 3:1 (to the climber) or it's not. The amount of force the climber has to apply won't change just because we call it something. It is what it is.

Hmmm, as I re-read that, it sounded a little harsh - not intended that way at all. Just trying to be succinct. So sorry if it came across that way.

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It's interesting that we can immediately see that a frictionless RADS will have a 2:1 ratio when pulled by a ground referenced person. We seem to have no problem realizing only two strands of rope support the climber and the upper pulley is merely a 1:1 redirect.

Where the problem comes is when the climber pulls the down rope. We can't seem to see that when he pulls, three strands are supporting his weight. That's a clue - three strands support his weight. If he had to hold one of the strands, the pull end of course, how much force is in that rope? One third his weight. He's pulling his full weight up with a force of 1/3 his weight. How can that possibly be true if the RADS is a 2:1 with respect to the cliimber?

Here's some simple tests and hopefully food for thought:

1- Tie a rope to a limb, connect an ascender to the rope and see if you can pull your entire weight off the ground with nothing but one arm. I doubt anyone on this board can do that. How much force would be in the rope if you just hold yourself in one place off the ground?

Ans. the force in the rope will be the same as your weight.

2- Tie a pulley to the limb and run a rope through the pulley. Tie one end to your harness and put the ascender on the other end. See if you can pull your entire weight off the ground with nothing but one arm. I suspect just about anyone can do that. Why can we suddenly lift our weight with one hand when we couldn't before? How much force is in the rope?

Ans. We can lift our weight because the arm doing the lifting in this pulley configuration only has to pull 1/2 half our weight. When we raise a weight with half the force, we have a 2:1 MA.

The force in the rope: There are two strands of rope supporting our weight, the end tied to our harness and the end we're holding via our ascender. Because the rope is run through the pulley, the forces in each rope have to be equal. So our weight is divided equally between the two strands of rope. So how much weight is in each strand? One half our body weight - that's why we can suddenly pull ourselves up with one hand - we only have to pull half our body weight. Hence, a simple pulley, where the climber is pulling himself is a 2:1 system.

If you watch my video, I'm on this very system and pull myself off the ground and hold myself with one arm! We don't think I can generate 200 lbs of force with one arm do we? So what's the trick? The trick is the pulley system described above is a 1:1 redirect to another person(s), but a 2:1 to me, the climber.

The RADS works exactly the same way except there are three strands supporting the climber, hence the inexcapable conclusion, the RADS, to the climber, is a 3:1.

What's very interesting about this is I beleive if we'd just go out and try to climb with nothing but our arms on a single rope, a rope over a pulley, and a rope in a RADS configuration with the Grigri replaced with a pulley, we'd have no doubt whatsoever which one is a 1:1, 2:1, or 3:1.

 

[DSMc]

[ QUOTE ]
I understand what you're saying. But consistently calling something incorrectly won't make it correct. If I call black, pale white consistently, then I'd just be consistently incorrect.

However, the theoretical MA of a RADS system is not a 'shade of gray' nor 'tomahto/tomato', it's black and white. It's either 3:1 (to the climber) or it's not. The amount of force the climber has to apply won't change just because we call it something. It is what it is.

[/ QUOTE ]

Well said and not too harsh at all, Ron. Like I stated previously, there are so many times our work doesn't have a simple answer; we should relish the things that do.

Dave

 

[treebing]

Nice video Ron, I can't imagine why you would want to call it a 2:1. But if that is how it makes sense to you and you only use ground references to explain things. Like its a 2:1 system but the climber is pulling.... I don't know Taylor video makes it seem like he gets what is going on but has a different vocabulary. I find it confusing but if you keep it consistent than good. I definitly advise against teaching it that way because it will confuse the hell out of people. For me, I would prefer to use the terminology that has been in place in physics classes for the last several thousand years.