Inflatable spreader bars?

[autox]

Actually, considering Cmoulder's pole specs, making them an inch longer at each end for fabric pockets would be lighter.

[cmoulder]

Hey guys,

I've been enjoying this thread and learning what the state of the art on UL bridge hammocks is. Very informative.

Cmoulder, if you arrive at a 4oz set of spreaders, that will indeed address the ends I was hoping to reach with inflatables. Life has gotten in the way of further work on that from my end. I think I'll just wait and see how you fare.

On that note, have you considered making a 2 segment pole with an off center split? Saves the weight of a ferrule. 12"/24"?

Is there a reason metal end fittings are favored over fabric pockets? Or how about this: cut a 1.5" segment of ferrule, glue on a 1/4" segment of pole stock 1/4" from one end, drill a <1/4" hole in the short end of the ferrule (yup, just barely fits), run your suspension line through that, and finally insert the 1" end in to the end of your spreader bar. This will require some adaptation to get it to work, but you get the idea. All carbon fitting the inserts in to the end of your pole. The insert length can be rather short as there no bending moment around the pole tips. Maybe wrap some adhesive Velcro around your pole ends to secure the inserts via a mating strip attached to the suspension.

The plugs/fittings I plan to use on the ends will contain very little (or no) metal, depending on how it's done. And you are correct... once the pole are inserted, compression forces hold them in place without any help, so even the Velcro assist is not necessary. One time I was playing around with the hammock in my local woods and it was very windy... with no load in the hammock and with it spinning and whipping all over the place, the pole tips did not separate from the hammock.

I thought about fabric pole pockets early on but JB convinced me they are not a viable alternative.

The ferrules are going to weigh about 7.5g each, so there's an area to shave 1/2oz. I plan to use long ferrules (5"/125mm, 2.5" overlap in each tube) so having the joint slightly off center will work. I like pole sections that fold evenly, and sections of 16.75" (glued ferrule end) and 19.25" would achieve that end. Those would fit nicely (vertically) in a side pack pocket.

That puts them at 2.8 oz, which means that with tips <4 oz is quite realistic. Using non-metal tips an no shock cord, 3.5 oz is not out of the question.

[autox]

Can anyone elaborate on why fabric pockets aren't viable? The only challenges I see are in how to prevent them from sliding on the suspension, which isn't that hard to solve, and the fact that they'll apply a radial compressive force on the ends of the poles which may (or may not) require some re-enforcement to resist.

I don't think moving the pole split just a half ferrule length off center is adequate. Think of how a straight tent pole flexes in to a hoop. It's true that the bending load peaks dead center, but it's still relatively high for a ways out to each side. But if you've already visited this problem, you actually know, while I just have theory.

[cmoulder]

I'll try to find a passage where JB has elaborated on fabric pockets, but my rudimentary understanding is that they mess up the geometry, and for bridges this is a very critical aspect.

Besides, the alternative is actually much lighter... no pockets!



I'll definitely play with the ferrule idea some more before committing. My 'feel' for the CF material tells me that the ferrule location will be okay as I've described it because of the impressive rigidity of the 16mm tubes. More important than location is fit — very precise fit equals zero slop and evenly spread forces.

I have some fixed-length, 2-piece trekking poles made with 13mm/1mm tube with 11mm/1mm ferrules that are 100mm long (50mm - 2" overlap each end), located dead center in 117cm poles, and these are very robust. I've shock-loaded and flexed the hell out of them quite a few times with no damage. A couple of times I would have sworn they were goners but somehow they survived unscathed.

[Just Bill]

Nice to keep this going... to jump back in:

OVERALL- Grizz (as usual) titled his video appropriately:"Counting grams". So keep in mind what follows is an overly anal analysis of the various items involved with the goal of pushing further than before.
Also worth noting... I will suspend my general design philosophy that stuff should be easy/intuitive and reproducible. So rather than a once in a lifetime DIY... I tend to focus on off the shelf stuff that people can actually use or buy... but if you are building a one off for personal use there are a few things you can try. Being an 'owner/operator' means you can do some things even if they are a pain in the *** you might not normally ask a customer to do. (like sleeves or funky pole tips).

On the fabric pockets/sleeves/etc:
Counting grams is the primary line to follow here... as a result I generally dismiss the idea simply because of weight. As Cmoulder's excellently blurred photo (Thank you) shows... nothing lighter than nothing.
So avoiding any excess bridge nerdery... let's just focus on what you're exchanging.
Though it is important to point out that adding pockets does then add other concerns and geometry changes... even more so on the recessed bar bridges I tend to build. Those changes may also cost you grams or create new points of stress/point loading that needs to be dissipated or addressed.

A pole tip is the primary means of finishing things off. So we have to start with that: https://1drv.ms/f/s!Apygyt54yYPwhIQSBMn1QgoqiBBj-w
What we have there is the .625 locking tips at 30.5g or 7.625g each. Next is the .490 locking tips at 22g or 5.5g each.

Cmoulder- as a side note: These are the compression tips... slightly larger than the shock cord tips if you're having fit issues. I'd think regardless of what fits- there is no need for shock cord no matter what? I'd think epoxy would be enough to anchor these as mainly you're just securing them so they don't fall off in transit. Once in the bridge they can't fall out.

The tips do several things for you:
They plug the end of the pole itself; which solves the radial compression force mentioned.

I'm not a carbon fiber expert, but my understanding is that the ends are a weak spot period... including the chance the fibers could be frayed or damaged.

In theory you could just cut a notch in the tube like an arrow knock... but I believe that would simply split the pole at some point?
IF NOT; I suppose that would jump to the top of list if it was structurally viable as once more... nothing lighter than nothing. In further theory... I suppose you could fill the end with epoxy to plug it and stabilize the fiber itself prior to adding the knock/slot for the suspension. Though in the name of counting grams the epoxy plug has some weight too.

Because of the way the metal tips are made, they not only fill the tube internally, but the end of it caps the tube itself to ensure that any compression force on the tip is transferred cleanly to the pole shaft. So you get a plug and a bearing plate. That cap also protects the CF from any potential damage, cracking, etc.

The other big thing the pole tip gives you is they provide is a way to interact with the bridge suspension itself. Which is also very secure and unlikely to be bumped out during setup or use. When you're in it... the pole shouldn't move... but until you are in and settled there is always the chance of jarring the pole loose.

So the way I see it:
1- The pole tip is a pretty elegant/easy to repeat solution.
Not really explored much would be drilling it out a bit or cutting off half of the plug (since it's solid) if you wanted to create the lightest possible aluminum tip. I'd imagine 1-3g per tip as a guess? You need a drop of epoxy per tip to secure it... but overall let's just guess you could go down to 15g or 25g for the set of 4 as a baseline to compare.

2-Pockets have to built out of something durable enough to contain the pole without damage... An easy example would be 2" webbing. Which weighs about 11g per foot.
You'd want about 2-3" of pole running past and into the pocket. You also need to sew a loop to slip over the dogbone. (think flashlight holster with belt clip.)
So that's about a foot per corner... or 44g total. So that's the general lack of viability issue in my opinion. You also need to add a minimum of 8" (2" per corner) of pole weight and epoxy plugs.
Could you use 1.5" grosgrain? Maybe, but you'd have a hard time getting enough stitching in. At 9g per foot you're down to 36g (still higher than the tips).

Could you fold up a heavy fabric like Robic 420, Hybrid 300, or even Hex 70/Hexon 2.4)... perhaps. Maybe you get to 20g?
But you are still not counting epoxy plugs, extra pole length, or any structural repercussions to the bridge as a whole.
You also are not considering you just added 4 points highly subject to failure even if you can crunch enough grams to justify it.

So overall... my take on pockets is they make trekking pole adaptation possible for some. For that reason they have a valid application.
But for SUL bridge construction they are not viable simply because the grams don't count up too well.

It sounds like we need to leave Cmoulder to playing with what I imagine is a set of increasingly smaller pole nested together with a stub's worth of pole to act as the tip?
I honestly don't know but... if you drop the pole will that 'tip' shatter?

One interesting point in that ramble though?
An epoxy plugged end with an arrow knock connection would require an extra 3/4" or so per end (3" total) plus the weight of the epoxy to fill say an 1" of tube?
I have no idea if that is a viable solution structurally... but kinda figure it might add up and you'd be down to debating this untested method to save 10g or so vs the pole tips?
Maybe I'm overvaluing the epoxy weight... or underestimating the poles. But 'nothing lighter than nothing' so while the pole tips are more repeatable for production maybe this might be viable competition for a one off design?


Poles- Agree with Autox's thoughts in general on the SUL segmented poles.
A- two segments (rather than three) cuts down on ferrules
B- Doing a roughly 1/3 to 2/3 split is stronger than an evenly packed length. Though I understand the appeal of the equal length two pieces and that's how Ruta Locura makes up his for that reason.

But if pushing things further then I'd err on the side of caution. When I had to split the .490 poles up I split the 26" into an 17" with no ferrule, then the 9" with ferrule for an 11" finished size. I was able to support at least 200lbs this way I did one pole to try in a clean split/centered joint but it was pretty sketchy and felt a hard fart or bad bounce away from snapping. If I recall correctly it held me while I sat down, but I was too scared to laydown under it.

So for this thin wall first attempt... I'd go with a thirds approach for the basic design.
Despite the pack up concern... I think we all agree that is the strongest design with one ferrule.


For my part- did three new prototypes over the weekend:
https://1drv.ms/f/s!Apygyt54yYPwhIQbFV8nsL7sPey2VA

I worked on my Luxury size (largest recessed bar) bridge with a hybrid construction technique- A Hexon 1.6, a Hybrid 1.7 and a Hybrid 1.2.
The CF poles are a three piece head pole nesting set that weighs 7 1/8 ounces.

No suspension in there- but 17.75 ounces is impressive (down from 20.5/21 ounces normally). So that's about 15% lighter for a 225lb occupant rated bridge.

The hybrid 1.2 model would hold roughly 180lbs or so. I didn't have dynaglide spliced up and I did add the pockets... so that 15.25 ounces could be under 15.

That said... this was mostly just for fun and to test the concept of the construction method moreso than pushing anything crazy.

I'm doing a batch of Happy Medium next and plan to try a few hybrid models in there to see where that goes. (36" recessed bar)

I sketched up a Harmony prototype as well... Initial thoughts would put that at about 12.25 ounces in a 1.6/1.7 fabric or 11.25 ounces in Hybrid 1.2.
That's with the current 5.5 ounce set of poles in there....

So if a 3.5 ounce 36" set materializes... there may be a bridge waiting for them that would take that down to the 10.5 ounce range for a full size bridge.

As mentioned... a 30" fixed bar might allow you to push further... but I'm not sure if that last ounce or two is worth it other than just to say it's been done.

[cmoulder]

JB, it's very cool to see this work you're doing for LW and UL designs. One doesn't have to be a bridge person per se to respect all the thought and work you've devoted to this market niche, of which you seem to be the only occupant at present! You might soon be holding the world record for lightest bridge.

For the pole tips, I have leftover bits of 13/11, 11/9 and 7/9 (mm, OD-ID... from previous projects) to build up some tips along with the 15/13 that arrived in the mail just this afternoon. I'm going to have to weigh the CF rod and Al pole tips to see which option is lighter. The tips I got from Quest are tent pole tips and not plugs, so they might actually be lighter. I'll do photos to show the design and assembly.

This 15mm ferrule stuff is a perfect fit inside the main 16mm tubes — nice n snug, but slides cleanly. The 500mm piece weighs 29.9g, so the the actual ferrule weight @125mm is going to be right at 7.5g as estimated. Plus a teensy-weensy bit of JB weld (Kwik variety). 15mm with 0.5mm wall could have cut that in half but I couldn't find any 15/14.

Leaning strongly toward eliminating the shock cords... 2 sections aren't going to get annoyingly jumbled. Easy enough to add later, perhaps. I'm still favoring equal lengths of 19.25" but I'll test-fit a ferrule and play around with it first to get a feel for the rigidity.

[Just Bill]

It's very cool that your long term interest and experimentation with trekking poles is contributing full circle to this project as well.

Technically, I currently hold the 'world record', lol. Though other than Grizz acknowledging the Micro was lighter than his current UL offering that's about the extent of the fanfare involved.
While I drink plenty of Guinness, they have not as of yet come by my shop to put me in their book.

What's more exciting in my opinion though... is that I'm beginning to apply the (arguably silly) micro lessons to much more practically sized options. The 8 ounce small neo-air is truly cool and light... but the 12 ounce large size is much more practical to use. So to some extent I feel that's where we are getting at the moment... an adventure in minimalism that we can bring back to the real world and apply to gear you'd actually want to use.

Ultimately it's a string of us here, which is why I try to also openly discuss and encourage others as folks did on my behalf. As often happens... Autox opened the discussion with a different idea that led to other ideas... and the chain of ideas builds. For me it's mainly Grizz, who built upon TeeDee and a few others here and was so generous with not only his time, but in conglomerating the collective efforts of those before him into a digestible format that helped so many 'catch up' to the state of bridge design at that time. Grizz was really the one pushing the envelope with Gossamer Gear trekking poles to adapt them to a bridge and shave out the pole weight... so that's why I say your efforts with trekking poles really are bringing this full circle.

It's also full circle for me... as one of my early contributions was to push things with Aluminum poles... so seeing that done with Carbon Fiber is exciting as well. And very promising.

I follow you on the CF pole tip construction, and I think if you get down to a 16mm main with a 9mm tip that should be enough shoulder to get a good seat with the 2mm dynaglide.
You'd probably want to fill that last tip solid with epoxy... but there is one more trick to reduce compression force on the tip itself if needed... but ideally it can work as it currently does because slipping the tip in as you have shown with your trekking pole reduces the pinching/crush out of the 1/2" webbing loop and lets that connection last longer.

On the aluminum tips:
There are two flavors; the compression fit and the shock cord fit. Both are slightly different sizes for the insert portion. Really for this use though; whichever fits the CF poles best is all that matters.
I'm taking an educated guess (since I don't have a caliper to verify) that the compression is slightly larger than ID, the shock cord tip slightly smaller... giving you a half mm or so of options in each size.
If you want me to send some of the .490 and .625 compression fittings to play with I can do that. Looking at the easton chart at Quest- https://www.questoutfitters.com/tent_poles.htm
I think simply grabbing a dremel tool and lopping off the last 1/4" or so of the insert would reduce weight a good bit- but doesn't look like it matters.

The ID of .625" poles is 13.94mm... so likely too sloppy for the 16/15 tube but too big for the 15/13 insert.
The ID of .490 poles is 11.12mm... so again you're necking down with inserts and still getting a sloppy fit. Though likely the shock cord version is a clean 11mm.
So it may prove out that without milling them; none of these off the shelf pole tips work well and you are relegated to building up a CF tip regardless.
I might have a .433 tip left over... That would be closest to 9mm and actually matching a CF pole.

Doing a shock cord is surprisingly heavy... and more annoying than you might think in the field. The bridge suspension always wants to pull the tip out when you remove the poles.
So regardless I would eliminate it and if you go the AL pole tip route just plan on gluing whichever one in that works. Handling the two segments isn't bad and there are other reasons down the line to keep them separated too.
Also simply fits in with the 'nothing lighter than nothing' idea... a drop of glue is something but you get the point.

Maybe I'm imagining the multi-tube build up (or working with CF in general) as more of a pain in the butt than it really is. I try to stick with off the shelf stuff with production/sales/end cost in mind.
But I suppose if the CF tube cuts clean/easy and there is minimal hand work that nesting several small sleeves into a tip would be ideal in many ways. I'm just picturing rough cuts with some sanding needed as that's sort of how doing the custom AL poles I made went... It could be done for a one off FKT model or demonstration piece... but simply tapping in the compression fitting and sticking with stock poles is the only way to keep it affordable for the masses.

All that said... I haven't reached out to Josh at Ruta Locura yet. I look at this as your project and as I said to Autox earlier... sometimes it's best not to bring in an expert to tell you what is or isn't possible because sometimes you can lie your way into a solution.
Josh does mill his own metal tips for his poles in his shop. So the option is there at some point for you to work with him to get custom tips made to match the poles.
Dutch has a CNC machine as well and I often debate if Titanium tips would be the ideal solution long term to pair with a thin wall CF tube... but one problem at a time, lol.
Let's see if the thin wall tube does the job.

Either way... I'm excited.

[cmoulder]

Lots of options!

I have also thought about plastic for the tips, which a gunsmith friend can mill for me on his lathe... maybe Delrin or the very hard glass-filled stuff. However, dense plastics might not weigh less than Al, and almost certainly not less than the CF lay-up I have in mind.

But you're right about getting a little ahead here. I've got some spring cleaning projects going on right now but I'm pretty sure I'll have them ready in a couple of days and we'll find out if they pass the critical crunch test.

[cmoulder]

And I stand corrected... I should have said "breaking your own World Record" ... like Vasily Alekseyev did so many times back in the '70s.

Also, I would imagine he owns the record when it comes to breaking one's own records.

[GreatBigDave]

...have you considered making a 2 segment pole with an off center split? Saves the weight of a ferrule. 12"/24"?...

...The ferrules are going to weigh about 7.5g each, so there's an area to shave 1/2oz. I plan to use long ferrules (5"/125mm, 2.5" overlap in each tube) so having the joint slightly off center will work. I like pole sections that fold evenly, and sections of 16.75" (glued ferrule end) and 19.25" would achieve that end. Those would fit nicely (vertically) in a side pack pocket...

...Poles- Agree with Autox's thoughts in general on the SUL segmented poles.
A- two segments (rather than three) cuts down on ferrules
B- Doing a roughly 1/3 to 2/3 split is stronger than an evenly packed length. Though I understand the appeal of the equal length two pieces and that's how Ruta Locura makes up his for that reason...

As the bridge requires two spreader bars, you can readily size them to pack into three equal length pieces split once at about a thrid of the length.

You'll need:
Long Pole length, Short Pole Length, Tip Length(outside the pole), and Ferrule Length.

You'll Calculate:
Total Pole Length = Long Pole length + Short Pole Length + (4 x Tip Length)
Packed Size = (Total Pole Length + (Ferrule Length / 2))/3
Long Pole Long Section = Packed Size - Tip Length
Long Pole Short Section = Long Pole length - Long Pole Long Section
Short Pole Long Section = Packed Size - (Tip Length + (Ferrule Length / 2))
Short Pole Short Section = Short Pole Length - Short Pole Long Section

Ferrules are bonded in the Long Pole Short Section and Short Pole Long Section. Short sections connected together when packed.

Example:
Long Pole Length: 38
Short Pole Length:34
Tip Length: 1
Ferrule Length: 4
Total Pole Length: 76
Packed Size: 26
Long Pole Long Section: 25
Long Pole Short Section: 13
Short Pole Long Section: 23
Short Pole Short Section:11