3/4 UQ questions

[Schneiderlein]

darts aren't so hard to understand. basically if the shells are different sizes, they will not fit together, there will be extra length on the larger one. the darts make it so the edge of the larger shell will fit onto the edge of the smaller one, they take up the slack.

The problem I have with darts is that they make things 3D - the fabric does not want to be flat anymore after putting in a dart. It is somewhat hard to visualize that for me.

Part of the problem is that I do not really know what exactly the shape is that I am trying to make the quilt conform to. If it were just a half cylinder, the problem would be easy and no darts would be needed. But there is a roughly conical section at each end. That's why rectangular quilts need to be cinched up. If you put darts in, you can make the quilt conform better to the ends, and it would not have to be cinched up. This should have the additional advantage of the sides in the middle section having less of a tendency to fall away from the hammock.

I was thinking that instead of using darts, one could use a separate fabric panel for each chamber of the quilt. Sort of like an old-style soccer ball or a beach ball. If you have a good idea what the shape you are trying to make is, the panel shape is still pretty easy to work out.

Where I get lost is trying to figure out how the panels would have to be cut for a quilt with different coverage along the length. One cannot simply taper the panels because the quilt will become conical, or at least I think that's what would happen. And that's where my head starts spinning every time I think about it.

I guess Grizz is the math guru here. Maybe he can come up with an equation and a program (hopefully not in perl) to compute the optimal panel design for a given hammock shape. But then again, he doesn't need much of a program to figure it out for his hammock...

Oh, btw, I just arrived in Albuquerque and went to Walmart across from the hotel to pick up some snacks. Of course, I had to stop by the fabric department. Got 10 yards of olive 1.1 ripstop with DWR. There are about 30 yards left, in case anybody is interested. It is the Walmart on Menaul.

[warbonnetguy]

if you want to make a really good one, don't assume it will happen on the first try. you may have to play around with some of those ideas a bit to get them to do what you want.

[GrizzlyAdams]

The problem I have with darts is that they make things 3D - the fabric does not want to be flat anymore after putting in a dart. It is somewhat hard to visualize that for me.

Part of the problem is that I do not really know what exactly the shape is that I am trying to make the quilt conform to. If it were just a half cylinder, the problem would be easy and no darts would be needed. But there is a roughly conical section at each end. That's why rectangular quilts need to be cinched up. If you put darts in, you can make the quilt conform better to the ends, and it would not have to be cinched up. This should have the additional advantage of the sides in the middle section having less of a tendency to fall away from the hammock.

I was thinking that instead of using darts, one could use a separate fabric panel for each chamber of the quilt. Sort of like an old-style soccer ball or a beach ball. If you have a good idea what the shape you are trying to make is, the panel shape is still pretty easy to work out.

Where I get lost is trying to figure out how the panels would have to be cut for a quilt with different coverage along the length. One cannot simply taper the panels because the quilt will become conical, or at least I think that's what would happen. And that's where my head starts spinning every time I think about it.

I guess Grizz is the math guru here. Maybe he can come up with an equation and a program (hopefully not in perl) to compute the optimal panel design for a given hammock shape. But then again, he doesn't need much of a program to figure it out for his hammock...

Oh, btw, I just arrived in Albuquerque and went to Walmart across from the hotel to pick up some snacks. Of course, I had to stop by the fabric department. Got 10 yards of olive 1.1 ripstop with DWR. There are about 30 yards left, in case anybody is interested. It is the Walmart on Menaul.

The separate panels you're thinking of, run across the narrow width of the quilt?

Thinking out loud here, last night I stumbled this old post by the uberlight guy gardenville, where he made an overquilt of separate chambers and slipped that into a cover. Maybe there's something in that approach to be learned/tried here....if one can figure a way to have the inside hanging from top side of the cover rather than being held up (and compressesd) by the bottom side.

time for more coffee.



darn it. I was in ABQ just 2 weeks ago. I don't normally go cruising Walmarts though when I'm on the road. Usually too busy.

Part of the conforming to a hammock shape thing is solved with the snugfit by using micromesh spandex on the underside. It's a place to start anyway, before diving into the details of differentially cut baffles.

Grizz

[Schneiderlein]

if you want to make a really good one, don't assume it will happen on the first try. you may have to play around with some of those ideas a bit to get them to do what you want.

That's what the $1 fabric is for. Now all I need is time.

[Schneiderlein]

The separate panels you're thinking of, run across the narrow width of the quilt?

Thinking out loud here, last night I stumbled this old post by the uberlight guy gardenville, where he made an overquilt of separate chambers and slipped that into a cover. Maybe there's something in that approach to be learned/tried here....if one can figure a way to have the inside hanging from top side of the cover rather than being held up (and compressesd) by the bottom side.

time for more coffee.



darn it. I was in ABQ just 2 weeks ago. I don't normally go cruising Walmarts though when I'm on the road. Usually too busy.

Part of the conforming to a hammock shape thing is solved with the snugfit by using micromesh spandex on the underside. It's a place to start anyway, before diving into the details of differentially cut baffles.

Grizz

The panels are supposed to run along the length of a quilt, like a snugfit. Imagine the panels on a beach ball that has a cylinder section inserted at the equator and is cut in half the other way. Only more panels. The problem I have is reducing the width while keeping the radius on the cylinder the same. I think that's only possible if every panel has a different shape, clearly not what I want to do.

The cutting would already be a bit of a pain with all panels the same for each side of the quilt. Anybody have a suggestion for a hot cutting rig that works? I have seen mention of using soldering irons, but no specifics.

Does the micromesh gather the fabric, or do the darts reduce the radius at the end such that no more gathering is needed?

I don't normally go to Walmarts, either, it was pure coincidence. I needed bottled water and a bite to eat, and the Walmart was right there. I may have been to a Walmart twice in the last 3 months. Both times I found fabric.

[GrizzlyAdams]

I can visualize the beach ball, and can imagine the sections being defined as the interiors bounded by vertically oriented planes that contain the straight line between the north and south pole of the beach ball.

So then the cylinder models the human body? With, for example, the longitudinal axis lying in the plane that contains the beach ball's equator? No wait. If the cylinder is the body, then it is oriented the other way, with its longitudinal axis passing through the ball's north and south poles.

And so, (getting to the point at last), the business about changing the radius of the cylinder is really meaning that the geometric solid used to model the human body is not a proper cylinder which one describes with two parameters (radius and height), but is something else. One possible something else you might mean is that along the length of this solid the cross-section is always half a cylinder, but the radius changes with position. Or you might mean that the object isn't actually a cylinder, but something whose surface at any point along the length is described by a radial function r(theta).

makes rocket science look easy

my business in ABQ was at Sandia. Far as I know they don't do rocket science, so maybe you were visiting Kirkland. Don't tell, I know, it's a secret.

Grizz

[Schneiderlein]

I can visualize the beach ball, and can imagine the sections being defined as the interiors bounded by vertically oriented planes that contain the straight line between the north and south pole of the beach ball.

So then the cylinder models the human body? With, for example, the longitudinal axis lying in the plane that contains the beach ball's equator? No wait. If the cylinder is the body, then it is oriented the other way, with its longitudinal axis passing through the ball's north and south poles.

And so, (getting to the point at last), the business about changing the radius of the cylinder is really meaning that the geometric solid used to model the human body is not a proper cylinder which one describes with two parameters (radius and height), but is something else. One possible something else you might mean is that along the length of this solid the cross-section is always half a cylinder, but the radius changes with position. Or you might mean that the object isn't actually a cylinder, but something whose surface at any point along the length is described by a radial function r(theta).

makes rocket science look easy

my business in ABQ was at Sandia. Far as I know they don't do rocket science, so maybe you were visiting Kirkland. Don't tell, I know, it's a secret.

Grizz

The cylinder model is of course, a very crude approximation using simple geometric primitives. The cross section in not a circle anywhere along the length of the hammock. What I was trying to say is that using several panels of an identical tapered shape will result in a cone, which is probably not really what I want.

Rocket science has many aspects. Sandia has a lot of nice facilities like sled tracks and centrifuges that can be used in the study of rockets. But I guess the common connotation of the term "rocket science" might be rockets that go into space, and not those that are meant to hit an object with great precision.

The beauty of this place is stunning. We worked late outside today, and the sunset colored the mountains in a spectacular red. Makes you think about hiking up those mountains, until you realize there are no trees to hang your hammock from...

[Schneiderlein]

I did a backyard test last night to figure out how a 3/4 UQ would work for me. I took the top quilt I made and doubled it over like Grizz did in his test. This gave me a rectangle of nominally 40"x50", but I measured 38"x49". I attached the quilt at the ends using shock cord. The shock cord was attached to the ridgeline using a Prusik knot, then looped through the quilt pull tabs and secured with a taut line hitch for adjustment. I attached the quilt so the baffles ran the long way, i.e., I had 49" of quilt going the long way, and ~38" across.

It was in the mid 40s when I got in the hammock and I didn't really think it was going to be a real test. I was wearing a cotton T, light weight fleece top and pants. When I got in the hammock, I was immediately warm. Not warm like with a pad, I was surrounded by warmth, and I had not even put the top quilt over me! I was thinking that I might not even need the sit pad for the feet, but after about 10 minutes I was proven wrong in that regard.

I felt all around the bottom to see how well the quilt fit and if the down was compressed. There was slight compression under my butt, and a very poor fit at the head end. I think I probably lost 6-8" of insulated length due to the poor fit at the head end. But I was warm so I did not bother making any adjustments. I put my 5osy Climashield XP top quilt over me and fell asleep. The birds woke me up at 5:45am, and I was warm, but had a bit of a cool spot on my right shoulder. I felt outside the hammock and noticed that my shoulder was right at the edge of the under quilt. I noticed a lot of condensation on top of my top quilt, but I felt no condensation on the bottom quilt. I got out of the hammock and it was coooold. The temperature had dropped to 34 degrees, and the humidity was at 90%.

Lessons learned:

• 3.5" of down loft under you keep you very warm in near freezing temps.
• 50" length appears to be sufficient, particularly when considering the ill fit at the top.
• 38" width would work for the ultra-light crowd, but I will add a little more width.
• I definitely need a pad for the legs, but I carry a sit pad anyway.

I am now convinced that the 3/4 length UQ is definitely worth pursuing. As soon as I find some time and a hot knife I will make a prototype. The quilt will be tapered at the head and foot end with baffles running the long way. I will try the exaggerated differential shaping design suggested by Youngblood.

[Schneiderlein]

I have started construction of a 3/4 UQ based on some of the ideas Youngblood and warbonnetguy put in my head. My hope is that the quilt will conform to the hammock much better than a rectangular quilt. To accomplish this, I have constructed both the inner and outer shell from seven panels each that are joined with French seams. For those counting grams, the weight penalty for doing this is roughly 0.8oz vs. using a single piece of fabric.

To make the pattern for the panels, I started out by drawing the width distribution that I wanted: 28" at the head end, 45" at the shoulders and 30" at the foot end, and essentially divided this distribution by 7 to arrive at the shape for each panel. I figured joining panels shaped like that should give me somewhat of a canoe shape. I wrote a little program to fit a B-spline to the panel shape. The program then extended the inner panel along its normal direction to add a 3/4" seam allowance for the French seams and also computed the shape of the panels for the outer shell. The quilt was supposed to have 3" loft, and I figured to split the nominal down volume between a baffle height of 1.9" and additional fabric width to accomplish the exaggerated differential shaping suggested by Youngblood. So the program computed the extra width required for the outer panels to achieve a volume equivalent to 3" loft. The program then matched the seam lengths of the inner and outer panels to the baffle. Throughout the program, I made extensive use of various approximations based the work of a famous 18th century Taylor. I won't bore you with all the details. To make a long story short, the program wrote a file that I took to Kinko's to get a print out of the template. I have attached an image of the template to this message. I will make the original pdf file available if this quilt actually works and there is interest.

So far, I have cut the panels and baffles with a hot knife. This took about 2h including setup and cleanup. I have joined the inner and outer panels with French seams, which took about 45min each. I am encouraged by the shape the fabric takes on if you hold on to the four corners. It actually does resemble the shape of a hammock. Unfortunately, I have had the flu for the past few days and have not been able to do much. I am feeling a little better today, but not well enough to go to work. With nothing else to do, I thought I'd post about my quilt.

[Schneiderlein]

I have finished the 3/4 underquilt aside from the pull tabs. The first photo shows the side of the quilt that goes against the hammock, the second one the underside.

The quilt has 26.5" insulated width at the top end and 43.5" insulated width at the widest point. The quilt is 51" insulated length. It is filled with 7.5oz of Speer down. I have not weighed it, but it should come in at about 14.5oz if my calculations are not too far off.

In the pictures, the quilt looks narrower than it really is because it is flat. As soon as you pick up the ends of the quilt, it takes on a hammock shape. Pulling on the sides only tightens the fabric layer that goes against the hammock, and does not compress the down at all. I am pretty excited about it and I think it will conform to the hammock very well.

My initial idea for the suspension system was to put four or five tabs along each of the long sides and run shock cord through them, sort of like warbonnetguy does with his quilt. I am now thinking that that may not be necessary and I can get away with just four corner tabs. I will start with that and hopefully get it under my hammock for a first test tonight. Unfortunately, the forecast low is 48 F, and there might be some thunderstorms coming our way. I'll try to get some pictures of the quilt under the hammock if it doesn't rain. My wife has agreed to help with this, but I am sure she does not want to get wet in the process.