Chair enlightening – 13 oz full chair

[Brian T]

Paul,

I ordered some .67 DCF to play around with, the REI fabric is quite light. 79.0 g on my scale, I am not confident I can make something much lighter than that but I am very interested to try.

The glass filled nylon joints are a big source of grams as well, I think I can make one out of carbon, but it’s a pretty complex part so it will take several tries to get one that is strong enough, light enough, and can be made more than once (doesn’t destroy the tooling).

I’ll keep y’all posted as I make more progress here.

[Pithawat V]

Funny that I asked a BPL forum a while ago about the idea of using carbon fiber tubes to save UL chair weight, and pretty much got ‘not worth it’ responses. Should have just go ahead and test out myself!

great execution, would love to hear how it holds up after long term use.

[Jason G]

I can’t imagine DCF holding up to the stresses of a chair. Much less .67oz!  I would probably start with 1.43oz.. but i still don’t see it holding up in the long run. I also think it would be annoyingly loud and crinkly every time you sit/stand/shift.

but hey, i’d love to be proved wrong

[Brian T]

Jason,
The fabric will require some trickery. At the stress points it will need to be significantly tougher, and sewing thing DCF creates some significant risks in terms of durability.

1.43 is up to the task, but a whale of a lot more expensive than the Nylon that REI already uses. There isn’t tons of room for improvement here anyway as the REI fabric is only 79g!

Here you can see it is pretty wicked light. It holds up just fine, but stretches and definitely is on the minimal side.

You can see here at the corners how they reinforced it is quite clever:

There is a pocket made of continuous ballistic Nylon inside the connection point that’s stiff and strong, but also means the pressure is not actually on the seam. The very point where the tube meets is not sewn at all but folded over, it’s sewn on the edge hem which is also multi layered. IMO this is the best seat fabric available. a lot more optimized and better engineered than the Helinox (even if a little more flimsy). A reasonable upgrade would be to put the REI skin on your Helinox chair as it would save you 1.5 oz.

[Brian T]

Pithawat,
I think it’s reasonable to assume it is not a mass market kind of thing. I’d bet an REI flex light air is manufactured for about $20. This would be a lot more expensive, and would only make sense if the grams savings were worth it.

FWIW I think the market might not be tiny, people already buy the flex light air for almost 2x the price of the flex light camp to save about a pound of weight. And the Nemo chair for even more than the Helinox when it weighs more.

Not for everyone, but to some of us, saving 25% or so is worth it. I’m having a blast with this project so I’ll keep posting as new things come up, My goal is to land on what set of optimizations are worth it for me, and see how they last in the wild.

[Jason G]

Yeah 79g aint too bad. you might be able to cut it to, what,, 55-60g? might be more trouble and risk than its worth.

 

What is the length of the longer sections of tubing for the chair? (assembled)

I wonder if you could multi-purpose or replace them..

1 idea would be to use them as backpack frame stays..  again, not sure how long the longer ones are, but perhaps you could combine them to make them the appropriate length. And most likely would have to be a MYOG pack..

Another idea would be to replace the longer sections with the tip section of a trekking pole. My BD Trail Ergo tip section is 21″.  If they are shorter than that it might not work, but if longer it could be cut to size.  Also might have to 3D print a cap to put on each end to fit the chair hardware better.

[todd]

Fun thread!  Great job.

[Brian T]

I just got some stuff in the mail today! :)

Here is something interesting things I discovered:
The flex lite chair fabric fits on the Helinox frame with little compromise (Helinox fabric is 144g on my scale and REI fabric is 80g) THIS IS A 2 OZ SAVINGS that can be had for $14
https://www.rei.com/product/205428/rei-co-op-flexlite-air-chair-replacement-seat

I also got some fresh DCF to play with today so I’ll be messing around with this some more in the coming days.

[Brian T]

Jason,
Really interesting idea on backpack stays. The rear poles would also get lighter if they were all one piece (right now they come apart like the factory poles). It would also save you a few grams on the shock cord which you could remove.
I think the biggest issue would be you’d need all the systems to work together. essentially you’d be making a pack just so you could bring a chair, and sort of designing the pack with two straight tubular stays that are easily removable for that purpose.

On trekking poles I keep going back and forth a bit. I think a lot of people use trekking poles for their tent, I am not sure what percent of people would leave their tent un-setup to use their chair, but it’s another good thought. I personally don’t use trekking poles so for this original version it didn’t really cross my mind until you mentioned it. it’s worth playing around with, but I think the connections (both to the plastic connectors and the fabric) will be troublesome, you’d need adapters of some kind and these are, IMO, the weak points of the engineering of these chairs anyway. They take quite a lot of torque at that point as the poles are like very long levers planted into those plastic lugs. I’ll play around with some dual use solutions for sure.

[Brian T]

one question for the group:

The Helinox Zero uses a rivet to hold the “center” horizontal pole in the plastic lug connectors. This prevents the legs from freely rotating, but it is effectively not replaceable (you have to drill out the lug and remove the aluminum, then if replacing it you’d have to rivet it again).
Questions:
1. Does this matter to anyone? This pole is the largest diameter (read strongest) and gets less torque than the others (read very unlikely to fail)
2. Would any of you drill out the rivet to replace this pole with carbon? It might save ~.3 oz (5-10 g), or would you leave that one as aluminum?
3. The analogous REI pole is currently shock corded in like the others, making it replaceable, but if glued in place the result would be lighter, and a little less creaky. (if you’re DIY’ing this it means you’d have to epoxy something), this would be an additional ~5 g savings in weight. Thoughts? There are some strength tradeoffs to not allowing the legs to rotate, however I think this is nominal.

[Stephen Seeber]

I happen to have both chairs, so I took a look.

Here are the weights.  Before weighing, I placed a 500 gram calibration weight on my scale.  It measured 499 grams.  A 20 gram weight measured 20 grams.

I sat in each chair with swapped fabrics.  As described above, the REI fabric has more stretch.  This could result from the construction differences of the back or be inherent to the fabric.  I found that Helinox fabric offers better lower back support on either chair.  I found the REI fabric to be less comfortable on both chairs for the same reason.  In terms of upper back support, I find that if I lean back on the Helinox chair, it flips over. So upper back support for this chair is less important. I find the leg configuration on the REI chair is somewhat more stable when leaning back.  I find both chairs sink on soft surfaces and flip if I sit down or stand up too quickly. I have learned to enter and exit either chair carefully, so I don’t sink or flip.

[Monte Masterson]

If you’ve already figured out how to cut at least 3 oz off the Flexlite Air, I wouldn’t worry about splitting hairs any further. Main thing is to get the field testing done and get a few produced to sell. Part of me thinks it would be impossible to beat the Helinox and REI engineers on making their chairs lighter and still maintaining comfort and durability. But on the other hand cottage gear innovators have shown themselves to be brilliant and able to cut weight in a way mainstream companies just don’t seem to do. Perhaps manufacturers think carbon is too expensive and therefore the MSRP would be a bit much.

I’d forget the pack stays serving double duty as chair frame. Probably would be a major PITA and the fiddle factor wouldn’t make it worthwhile.

[Brian T]

Monte,
I hear you, for now I’m focused on what you’re describing as first priority, but I still think there is significant room for more optimization. Practically speaking I am not sure the value prop for a customer gets better with more optimization. It could 2-3x the cost to shave a few more oz.

However, even if it’s only a 1-off, personal project I would love to achieve a chair at or around the 300 g range.

[Josh J]

Brian,

Great job! This has been on my mind for a very long time, I just wasn’t able to find couplings ect.

[Sam Farrington]

Flimsy, unstable, uncomfortable; but wow!  At 13 oz how can you go wrong?

[Brian T]

I have a question for the group:
does anyone here like this style of “chair”:
https://www.rei.com/product/217602/rei-co-op-flexlite-air-stool

I ask because this has a lot of room for improvement, and starts at 11 oz. I could think about working on this stool as well. (my back of the napkin is this could be 7-8 oz fully optimized)

I am curious to hear from folks who like this style seat. do you use something like this? in what circumstance? why do you like it? would a lighter version be interesting?

I am still working on the chair, but spending all this time thinking about this project has my curiosity going.

[Jerry Adams]

I can’t help myself, sorry : )

I would move that lower strap outside the legs so the fastener only had to prevent the strap from sliding up, not holding the full weight

[Bill Budney]

Brian: I like stools. They are lighter, quicker to deploy, and often taller. The taller height makes them more comfortable (at least for a short sit), and easier to hop on-and-off, for camp chores.

I am undecided about best use case, but a lighter chair makes the choice easier of whether or not to carry it at all.

Agreed with Jerry about that lower strap — it’s an odd design choice to put it inside the legs, when it is a structural part of the stool.

 

[Brian T]

By way of update on the original project here are some other experiments I have tried/ am working on:
1. I am trying to redesign the hub connections where the poles meet. They are currently made of fiberglass reinforced nylon (which is strong and light) but I am thinking I can improve on both the design and the material. This is a complicated part so it will take some time and may be an utter failure, but I am working on it.
2. I built a new chair skin from .67 dyneema. It was very close to holding my weight, however the pole punched through the material when I got full weight on it. This was actually a promising test. I think the trick will be laminating several layers of fabric in some areas (this is how the REI chair and the Helinox chairs work too. The “pole connection point” is the highest stress area. I came away thinking it will be a difficult engineering challenge, but it IS possible to make a lighter skin (might not be worth it lol)
3. I made a modification to my initial prototype where I glued the “center” pole in place. This is how the Helinox is natively designed, this prevents the hubs from rotating, but makes the center pole impossible to replace (at least without really significant work), however it saves 2g and improves the user experience of the chair IMO (it is more stable this way, although it applies a new twisting force to the center pole on some uneven ground). I assume people would prefer a replaceable center pole but I am not sure.
4. I would like to get some more miles on this creation and see the limits of the durability on these, so I am working on making more prototypes right now.

Thanks again for everyone who has commented on this thread the back and forth is really fun.

[Jason G]

Yea I would probably sew some 500d cordura to the Dyneema for the pole cups

[Brian T]

A few updates:
I glued the center pole on my first prototype (eliminating the shock cord and the two cord stoppers on that bar)

Here you can see where the cord stoppers used to be.

I also looked at the chair’s feet, they could be removed entirely, but it would expose the poles to a new type of damage (especially in carbon) but they could also be trimmed. Each foot weighs 6g, but cutting them shorter can save about 2g each (this is an 8g savings across all 4 legs

original

After a trim

Back on the chair
Together so far I’ve dropped a bit more weight as you can see here:

12.77 oz

By way of experimentation:
I cut up an REI chair fabric today, I removed the pole cups to see how much of the total weight is in these reinforced sections vs the rest. Here is what I found:
Total weight: 80g
Pole cups: 35.1g
Main fabric:  44.9g
I think that main fabric could be replaced, but I think best case scenario it could reduce the overall weight by <1 oz (22 g). The fabric cost on something like this would be more than the cost of an entire replacement fabric from REI, so it’s probably not worth it beyond a passion project, but still fun to work on.

Here you can see the pole cups are about 1/2 the total weight of the fabric on the chair.

[Brian T]

Sry double post somehow

[Alan W]

Brian, consider Dutchware 2″ wide spiderweb for corners. 100% UHMWPE, 3 g/ft, 1,500 lb tensile, puncture likely commensurate.

https://dutchwaregear.com/product/2-inch-spider-webbing-1-5-10-feet/

[Alan W]

PS. Spiderweb has worked well on the feet (not seat) of my chair, using for cross-x straps to stabilize on soft ground. So far, there is no  sign of feet poking through or abrasion wear despite thinness.

[Brian T]

Alan, Spiderwebbing is very cool, I had never seen it before.  by my measurement I could make a chair foot “x” and it would weicgh about 6g. I wonder if I could sew it in such a way I could eliminate the rubber feet since the ends would be protected by the webbing? this would be both lighter and better on soft ground. Very interesting idea….

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