# Thread: DIY Differential Cut UQ Calculator

Also this is the version i did with metric conversions
https://goo.gl/wQJPC4

this is the link you posted back at post #74 (11-April-2014),
with the menubar (so you can save it).

My next step is to add my formulas into a copy of the CatSplat calculator.

Here are my workings, so far, if you wish to see what is going on,
https://dl.dropboxusercontent.com/u/...ferential.xlsx

3. I am very interested in all this....

I made my second UQ attempt, a Wooki copy.

I took a far more crude approach but it has given me some great insight for the 2 quilts that I have made so far on the issue of differential cut.

My crude approach does not lend itself to max weight efficiency, as I knew going into it that if I am liberal with added fabric for the added shell in both length and width, I run the risk of adding unnecessary volume and need for added weight in down to fill it up.

I am baffled (tee hee) when thinking about the volume of each chamber in my wooki copy...each is a different length...added you have the differential and how it fills...and that each baffle has a tapered shape...wider at head end and tapers to skinny at the foot end. I just winged it by taking the width measurement of the baffles for the outer shell, baffle height + 0.5 and the length of that baffle at the center, and got the volume - divided by fill power, and added 15%...then for each baffle that was longer or shorter compared to that one, I added or subtracted a % from that point of reference.

I had to add more down to each perimeter baffle that was clearly a bit under-filled after letting it set (used magic clips to hold the open end)...after that all has seemed fine.

There has to be a better way...need to try out your calculator tonight and see if it gets me similar results.

I wont know if I underfilled the thing till it really gets cold...but it lofts up in spots to as high as 4.5 inches, lol...but as low as 3.5 in other spots...some of the way I shaped the baffles using pleats in both the baffle no see um strips and the perimeter of the outer shell fabric created some degree of unevenness, but I certainly avoided the compression upon hanging it like my first attempt suffered...is stuper puffy hanging under me...

Is there a way to calculate the volume of a chamber as a box but with very odd shaped dimensions like this...it would not need to be perfect as I don't mind wasting via some overstuff..? Well, at least I now have a point of reference to go off of if I ever remake this one...ill be interested to run some math and compare what the calculators spit out vs. what I actually did.

4. You might be better off duplicating the sheet, and having a separate sheet for each chamber.

The trouble with this calculator is it only deals with a single differential, not a dual differential.
When I made my dual differential UQ (here) I calculated the volume of the chambers by working out the mean width (by taking widths at regular intervals).
I made the outer shell width a function of the inner shell width as it varies along the length.

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5. It sounds to me like your method was pretty solid, PharmGeek, and the results look good. I would think the taper would cause each chamber to be slightly over-filled, which is not a bad thing.

Could your height differences be due to the chamber dimensions being slightly inconsistent? Or is it clearly the fill?

It may not take long for one of our resident mathematicians/engineers to come up with a way to calculate the volume of a tapered, curved chamber...

6. Originally Posted by KBr00ks
It sounds to me like your method was pretty solid, PharmGeek, and the results look good. I would think the taper would cause each chamber to be slightly over-filled, which is not a bad thing.

Could your height differences be due to the chamber dimensions being slightly inconsistent? Or is it clearly the fill?

It may not take long for one of our resident mathematicians/engineers to come up with a way to calculate the volume of a tapered, curved chamber...
I don't know...I mean I am extremely happy with the results I think so far..I was tinkering with it last night....the inconsistencies in some of the loft, is most likely I suspect just some of the variation in the amount of differential in various spots...the way I did it was to put in pleats...and how I did the pleats, or specifically where and exactly how many...I really did not plan that terribly well...what I SHOULD have done was pre mark on my baffle lines on both quilts where the pleats will be placed or concentrate....but mine were kinda all over the place...which was helpful in keeping everything nice and fluffy but created in this sense sorta some cosmetic inconsistencies.

Compare that to what WB does....from what I can tell the areas that are pleated off are coordinated such that when it lays flat for example...you see this crease across a straight line...Brandon has some wonderful people sewing for him! mine is so janky comparatively lol.

I think that combined with my imprecise means of adding down, gave some inconsistency...for now, I plan on rolling with it, because the lowest loft I think is like 3 inches...so I don't think ill bother adding more lol...

I am about to do yet another one, but it will be remaking my first attempt, my wife's UQ...the big orange one I made last year...it uses a very large rectangle so I am gonna try yalls updated calculator for that build....that rectangle is so wide, I have to sew extra strips of fabric to get the width needed for the outer shell, lol....

A2 = ((arc radius˛) * ACOS((arc radius - arc depth) / arc radius)) - (arc radius - arc depth * (SQRT((2 * arc radius * arc depth) - (arc depth˛))))
(where arc depth = Hc - Hb)
My brain hurts

8. I wondered what thread I read this in! It was an older post than I was realizing.

There are probably some assumptions built into this forumula as well - but I think that it is likely more accurate.
I was contemplating this the other evening - and got the impression taht the original formula assumed that the quilt was laying flat (which we know it doesn't do).
I was thinking that given a fixed perimiter, the maximum surface area is a circle.
Based on that - I was doing some calculations to compare the area based on CatSplat's original formula, vs what it would be if each chamber was filled enough to be a cylindar with the same permiter.
My assumption being that there would be some overstuff in each chamber if it were filled to that capacity.
I'm presuming that this will come in somewhere between those two numbers.

9. (From an earlier post)
This is how I worked the cross-sectional area of the chambers;

Chamber area = A1 + A2

A1 is easy enough, it's just the area of the outer circle minus the inner circle, take half that (for the area of semi-circle), then divide that figure by the number of chambers so;
A1 = (πR˛ - πr˛) / (number of baffle tubes * 2)

A2 is a bit more fiddly, the puffyness of each chamber is a function of the baffle height (Hb) and the max chamber height (Hc), it's the area of a segment of a circle,
A2 = ((arc radius˛) * ACOS((arc radius - arc depth) / arc radius)) - (arc radius - arc depth * (SQRT((2 * arc radius * arc depth) - (arc depth˛))))
(where arc depth = Hc - Hb)

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