Working against gravity ...

[DerekSmith]

@Roo

Although I applied a variable load, I did not take the load right off.

I will try that and report back.

Derek

[jcsampson]

So far, I have tried the Half Hitch (with and without Round Turns), the Clove Hitch, the Constrictor Knot, and the Strangle Knot.

I get the distinct impression that the best of these four--for this unusual context--is the Clove Hitch, because it seems to offer the best grip on the pole, for a sideways pull, considering the unusual context. Here's why:

For the other three, it seems that the securing mechanism--which generally offers a type of locking security for the construct, in most contexts--of each has a way of interfering with the ability of both of the ends of the rope to pull adequately on the turns of the construct (around the pole) in order to grip well the pole.

The Clove Hitch has no securing mechanism that can get in the way in this unusual context. . . .

Does anyone else notice this situation?

JCS

[DerekSmith]

@Roo

In the 3mm cord photographed, the Clove had a tendency to open when all load was removed, however, the weight of a 'gondola' might give the weight a Clove needs to stay set.

I also tried a 5mm hollow core braid (very soft) and this stayed set in all three knots although the Strangle probably performed the most consistently - without a loading weight, even the weight of the pole tended to be sufficient load to keep all three bindings under tension.

Derek

[roo]

@Roo

In the 3mm cord photographed, the Clove had a tendency to open when all load was removed, however, the weight of a 'gondola' might give the weight a Clove needs to stay set.

I also tried a 5mm hollow core braid (very soft) and this stayed set in all three knots although the Strangle probably performed the most consistently - without a loading weight, even the weight of the pole tended to be sufficient load to keep all three bindings under tension.

Derek

Since I happened to be working with some 3 inch plastic (ABS) schedule 40 pipe, I tied both constrictors and cloves on either end (in separate tests) with nylon rope.  I was unable to maintain the shallow angles of rope shown by the original poster, as the rope easily slid in both tests until the angles were much deeper.

[Transminator]

It looks like you need a knot/hitch that performs well when the pull is (roughly) in the direction of the pole
(sideways rather then at a right angle). The "Gripping Sailor's Hitch" from roo's notable knot index does exactly that.

http://notableknotindex.webs.com/sailorhitches.html

Would that be an option?

[roo]

It looks like you need a knot/hitch that performs well when the pull is (roughly) in the direction of the pole
(sideways rather then at a right angle). The "Gripping Sailor's Hitch" from roo's notable knot index does exactly that.

http://notableknotindex.webs.com/sailorhitches.html

Would that be an option?

The thing is, the application seems like a permanent installation.  There seems to be no reason to avoid drilling vertical holes in the ends of a cheap beam of wood (for example).  The hardest part would be taking the time to carve away any sharp edge on the lips of the holes where the rope presses.

One rope and a couple stopper knots seems very simple.

[jcsampson]

I like Derek's method because it's quick, easy, simple, and effective, and because it allows for the use of just one rope on each side--or even one rope for the entire structure, if, say, a Cow Hitch is used on the hardware at the top. (Of course, I also like the modularity of the methods that I presented.)

Here's another thought: The main concern with the use of one rope's intersecting the pole on each side by a Strangle, etc., seems to be the potential sideways slide. How about putting a Four-Coil-Ring Fixed-Gripper Coil Binder adjacent to each Strangle on the side nearest the center of the pole, to resist the potential sideways slide? Add more than one, if necessary: Sooner or later, there will be enough surface area successfully gripped to stop any sideways slide.

Alternatively, screw in a couple of, say, screw eyes to keep the Strangle, etc., from sliding inwards.

An edit follows.

Bronchen-Braten did mention, however, that "It's not a wooden plank[;] it's made from metal, [and] it's hollow . . ."

Another thought: How about putting a wide whipping at each end and then making Strangles over the whippings?

Unless I'm mistaken, it appears that Bronchen-Braten has put up a new photo of the swing, which shows a reworking: It appears that he has taken a rope around the plank LENGTHWISE and has made Clove Hitches around the loops of the suspending ropes. Very creative.

The things one can do with rope. . . .

JCS

[Bronchen-Braten]

First of all, thanks again for all the replies, I'm sorry for not posting anymore in my own thread - I did check on the first couple of replies several times, but I didn't notice there were so many new ones below, not to mention a page 2. These are many ideas and I'm sure most of them would work, only I'm having trouble following some of them, mostly due to language issues - I'm from Germany and unfamiliar with most specific notations regarding this matter. E.g. I can't imagine what whipping could mean in this context.

A well designed wrap will be stronger and grip better than a great feast of knots and holes.

That's why I signed up basically.

Unless I'm mistaken, it appears that Bronchen-Braten has put up a new photo of the swing, which shows a reworking: It appears that he has taken a rope around the plank LENGTHWISE and has made Clove Hitches around the loops of the suspending ropes. Very creative.

I have not added any new pictures, you may have missed the bottom one the first time - these are all the old constructions from about a year ago.

I have however found a solution which will do the job, I think - it's a little similar to the solutions shown in the pictures posted by derek, somewhat combined with jc's fixed gripper layout. My construction alone wouldn't have a good grip, but I have added a simple lashing strap on each side to keep the loops in place. So far it's doing fine, hasn't moved, and I don't think it will, as the horizontal pull is not THAT great, and they only need to keep it in place additionally to the naturally occuring grip. 

My very first idea was to use a metal pipe that could simply have the rope run through it. I went to several scrapyards and as it turns out, it's very difficult to get such a simple thing (one that is solid enough at least) - I could have bought one perhaps but I wanted to use what I had really, except the rope and the shackle.

Now off to the next problem: when tilted and moving at the same time, the gondola tends to wobble heavily to one side and I can easily imagine legs and other things being caught between the "cage" and the rope. That would be, well, bad. I wouldn't know a way to avoid that though. When I hand the gondola in a way that the two ends of the rope are parallel rather than V-shaped as they are now, then it would wobble less but they'd be closer together and that would end up in just as much leg-trauma-potential. Like I said, I did a couple of complete vertical 360? spins with the old one, but only when the rest was in a "resting" position. I don't know whether I should keep that move on the schedule or not.

I did not know about the rope leverage effect.

[DerekSmith]

Hi B-B,
Welcome back.

I am not certain that I have understood the nature of your second challenge, so forgive me if I propose an utterly meaningless 'solution'.

You describe the unwanted motion as being less prevalent when the suspending ropes are vertical and worsened when the ropes are angled.

From this I picture the unwanted movement as a sideways swing of the gondola towards one of the suspension ropes.  As this happens the rope on the swing 'to' side approaches more of a vertical position, while the rope on the 'from' side takes on an even greater angle.  The combined effect is to drop one side and lift the other - is this the motion you want to prevent?

If it is, then one solution would e to arrange for a sideways swing to shorten the 'to' side, effectively keeping the gondola level, or alternatively an arrangement that lengthens the 'from' side (or both).  An alternative solution would be to brace the suspension ropes such that their effective rotation point is shorter, so they have less effect for any given sideways movement.

These solutions unfortunately require cross diagonal bracing which will occupy the space above the gondola and so will violate your 'clear leg' space requirement.

One solution can e tuned to keep the gondola virtually horizontal when it moves sideways, but it is complicated and I guess that you are wanting to keep this as robust and simple as possible.  Still, I will describe the principle for you to consider while I have a 'play' to wee what else might prove effective.

Messy solution - This involves extending the suspension bar and fitting four pulleys to it - one on each end and two in the middle.  Then run a new cord from the gondola to the outermost pulley on its side, back to the mid pulley and down to the opposite suspension rope (about a third way down) and fix it to the rope. - Do this both sides.

When the gondola tries to move sideways, it hauls on the 'away' side line which through the pulleys hauls on the 'to' side rope, shortening it and so keeping the gondola level.

Away to think some more.

Derek

[Bronchen-Braten]

Once again I reappear after a long period of silence - I apologize.

The project is finished, rides have been taken and no one got injured.  I added another element to the construction - a long rope that is attached to the upper part of the top joint and runs from there over a pipe in the trees and then straight down to the ground (not the trees that hold up the gondola but the ones further back, to the side). This allows me to have "remote control" over the whole swing, as I can simply stand next to these trees and pull the rope, like ringing a big ol' churl bell. This sets the whole thing in motion and I was thrilled to observe how the rollovers happened completely by themselves.

The big premiere ("Trolley Twister") took place Saturday, September the 4th. I made a special music mix for the evening and put all my technical shenanigans (my usual film-equipment) on display, light-effects, a fog machine and so on, as well as a big set of speakers. A private fun fair if you will. The guests had no idea about this new 'ride' and were a little skeptical at first, but almost everyone had a go in the end and the reactions were very positive.

I uploaded a video "summary" of the evening to YouTube which I'd like to share with you:

http://www.youtube.com/watch?v=x9u4pLlZRmw&hd=1


Thanks for your support!

[Transminator]

That is insane!

Amazing what one can do with a bit of rope, the right knots and a vivid imagination.
I love it.

Greetings from a fellow (crazy) German
Kai

[DerekSmith]

Hi BB,

That looks crazy fun.

What arrangement did you finally finish up with?

Derek

[Bronchen-Braten]

I settled with a knot arrangement that isn't exactly professional but it will definitely stay in position. I pretty much just wound the rope four or five times around the metal beam on each side (like the loops used in the fixed gripper) and then added a belt in the exact position of the orange line from the image I put in my first post. So if the loops don't grip tight enough, the belts will definitely keep it in place, they won't slip either due to their shape, and they are easy to tighten.