View Full Version : black cat 2 tarp
The Breeze
02-13-2007, 22:37
just got mine finished 5 1/2 hours but man it looks good if I have to say so myself pictures to come tomorrow. this one I will take in the day light found a new way to make my cat curve thanks to ed speers. he was alot of help with lots of short cut and thanks to blackbisop for I could not have done it with out his input. pic to come now time to play.:cool: :rolleyes: ps. like the underquilt and top cover hope to never have to build anymore but problelly will till later peace:rolleyes: :cool:
Please share. I am interested to hear what shortcuts Ed has.
blackbishop351
02-13-2007, 22:51
I definitely am too - especially since, strictly speaking, there AREN'T any shortcuts to a "true" catenary curve.
Yeah I'm not saying the math held up to my sewing, cutting, and measuring skills. But I there is a decent amount of Trig behind the cat cut.
blackbishop351
02-13-2007, 23:01
Yeah I'm not saying the math held up to my sewing, cutting, and measuring skills. But I there is a decent amount of Trig behind the cat cut.
It's not even the trig that's the problem. Anybody in a HS geometry class (and those that REMEMBER HS geometry :p ) can figure the trig for the hex shape. The catenary function just isn't solvable in closed form for a given set of constraints. It has to be done numerically, requiring some sort of computer program.
The Breeze
02-13-2007, 23:08
instead of all the math that by the way Im not good at. you said 6in center point. took 7 foot of paper and a rope taped it to both ends and the wall. put it to the mark of 6ins traced cut out then folded 24foot or 8yards of black sil for a 12 foot ridge then folded inhalf to find true center then I marked three foot 1and a 1/4 inches then I cut the hex then cut the cat. both sides at the same time. now no matter how I fold it it is all even. hope this helps did it the country boy way with some help i might add .thanks everyone:cool: :D
It's not even the trig that's the problem. Anybody in a HS geometry class (and those that REMEMBER HS geometry :p ) can figure the trig for the hex shape. The catenary function just isn't solvable in closed form for a given set of constraints. It has to be done numerically, requiring some sort of computer program.
It's been so long ago:confused: . I might more in the terms of sine and cosine, then trig and geometry.
blackbishop351
02-13-2007, 23:17
instead of all the math that by the way Im not good at. you said 6in center point. took 7 foot of paper and a rope taped it to both ends and the wall. put it to the mark of 6ins traced cut out then folded 24foot or 8yards of black sil for a 12 foot ridge then folded inhalf to find true center then I marked three foot 1and a 1/4 inches then I cut the hex then cut the cat. both sides at the same time. now no matter how I fold it it is all even. hope this helps did it the country boy way with some help i might add .thanks everyone:cool: :D
OK gotcha. That should work fine, actually. For me it's just easier to mess up without precise measurements.
instead of all the math that by the way Im not good at. you said 6in center point. took 7 foot of paper and a rope taped it to both ends and the wall. put it to the mark of 6ins traced cut out then folded 24foot or 8yards of black sil for a 12 foot ridge then folded inhalf to find true center then I marked three foot 1and a 1/4 inches then I cut the hex then cut the cat. both sides at the same time. now no matter how I fold it it is all even. hope this helps did it the country boy way with some help i might add .thanks everyone:cool: :D
If it works, then go with it. Mine is tight except for the couple sewing errors I made. I might talk myself into a new one to correct this. It works fine just looks a little off, but then again so do I.
slowhike
02-13-2007, 23:27
instead of all the math that by the way Im not good at. you said 6in center point. took 7 foot of paper and a rope taped it to both ends and the wall. put it to the mark of 6ins traced cut out then folded 24foot or 8yards of black sil for a 12 foot ridge then folded inhalf to find true center then I marked three foot 1and a 1/4 inches then I cut the hex then cut the cat. both sides at the same time. now no matter how I fold it it is all even. hope this helps did it the country boy way with some help i might add .thanks everyone:cool: :D
that sounds like the way i would have to do it... the country boy way<g>.
i'm not much on math either.
blackbishop351
02-13-2007, 23:30
Just for general information purposes, I got a bug and checked my cat generator against the Excel file Youngblood posted on the Yahoo HammockCamping group. The test edge length and cut-depth were the ones I use - 74 1/2" edge, 1"/ft. cut-in. There was less than 1/16" max difference between my measurement results and his. This error will of course get larger as the edge gets longer.
Anyway, conclusive results - at least for a ~ 6' edge, his spreadsheet works just fine for calculating cat curves. I still prefer my data output method, though :p I also like the peace of mind that comes with knowing nothing's been "fudged"...but that's just the math geek in me.
Just Jeff
02-13-2007, 23:33
We have a mathematician and an engineer here. Easy to forget it's "cloth carpentry" and not astrophysics. :D
I would have hung some 550 on the wall and traced the arc. Close enough for a tarp, if not for a trig-based open-function computer-generated lunar orbit.
blackbishop351
02-13-2007, 23:34
We have a mathematician and an engineer here. Easy to forget it's "cloth carpentry" and not astrophysics. :D
I would have hung some 550 on the wall and traced the arc. Close enough for a tarp, if not for a trig-based open-function computer-generated lunar orbit.
Hey...I resemble that remark...and I HATE astrophysics, by the way! :p
We have a mathematician and an engineer here. Easy to forget it's "cloth carpentry" and not astrophysics. :D
I would have hung some 550 on the wall and traced the arc. Close enough for a tarp, if not for a trig-based open-function computer-generated lunar orbit.
I'm going to pretend you did not say that so that my world can go back to the way it was.:confused: :confused:
Just Jeff
02-13-2007, 23:40
Alright. How 'bout if I take it back? I would have used some kind of computer program to help with my cat curve. (Probably Internet Explorer and Hammock Forums... :p )
blackbishop351
02-13-2007, 23:42
HE, I think you should send Jeff that PDF paper I sent you the other night. Sounds like he could use some...eye-opening :p
blackbishop351
02-13-2007, 23:43
Alright. How 'bout if I take it back? I would have used some kind of computer program to help with my cat curve. (Probably Internet Explorer and Hammock Forums... :p )
I should probably insert some joke about the AF taking the easy way out...but I'm not military :eek: And besides, that's precisely why I happily provide measurements to anyone who wants them :D
Just for general information purposes, I got a bug and checked my cat generator against the Excel file Youngblood posted on the Yahoo HammockCamping group. The test edge length and cut-depth were the ones I use - 74 1/2" edge, 1"/ft. cut-in. There was less than 1/16" max difference between my measurement results and his. This error will of course get larger as the edge gets longer.
Anyway, conclusive results - at least for a ~ 6' edge, his spreadsheet works just fine for calculating cat curves. I still prefer my data output method, though :p I also like the peace of mind that comes with knowing nothing's been "fudged"...but that's just the math geek in me.
Disclaimer below is an engineering moment, but it pretends to hammocking in the context above.:D
The difference you saw may be in the math code built into MATLAB vs excel. I have seen differences in the results from my school work between switching from MATLAB 6.5 to 7. That usually only comes into play on FFT's, built in functions, or random number generators (not that any number is random). I would trust a $10,000+ engineering software package to a $100 microsoft program anytime. That also might be due to any rounding that is built into yours and his forumlas and code.
Or you could use a rope. But I can't bring myself to do that. I think the engineering police would come after me.:p
HE, I think you should send Jeff that PDF paper I sent you the other night. Sounds like he could use some...eye-opening :p
We could. I would attach my own work, but all my math is hidden in 10,000 or so lines of MATLAB and VB code. My thesis reads closer to a tech. paper than a math book.
blackbishop351
02-13-2007, 23:51
Disclaimer below is an engineering moment, but it pretends to hammocking in the context above.:D
The difference you saw may be in the math code built into MATLAB vs excel. I have seen differences in the results from my school work between switching from MATLAB 6.5 to 7. That usually only comes into play on FFT's, built in functions, or random number generators (not that any number is random). I would trust a $10,000+ engineering software package to a $100 microsoft program anytime. That also might be due to any rounding that is built into yours and his forumlas and code.
Or you could use a rope. But I can't bring myself to do that. I think the engineering police would come after me.:p
I thought about rounding errors - the Excel file only keeps 4 sigfigs, while I've set Matlab to use 12. However, the errors increase with the size of the curve measurement; they're larger in the middle and smaller at the edges. That seems to indicate a difference in the actual calculation, not roundoff.
I definitely agree on the difference in the software. Excel is made for accounting - not a high-precision usage.
blackbishop351
02-13-2007, 23:53
We could. I would attach my own work, but all my math is hidden in 10,000 or so lines of MATLAB and VB code. My thesis reads closer to a tech. paper than a math book.
VB?!?! :eek: Blasphemy!! **YECH!!!**
Jeff, don't ask me how this relates to hammocks...my imagination does have limits, being a scientist and all :p And thread drift concluded anyway!
VB?!?! :eek: Blasphemy!! **YECH!!!**
Jeff, don't ask me how this relates to hammocks...my imagination does have limits, being a scientist and all :p And thread drift concluded anyway!
Easy, I could be hanging in my room in my hammock. I'm not there right now, but I could be in a minute.:rolleyes:
That really doesn't pretain to it, I just wanted to rub it in.
Just Jeff
02-13-2007, 23:59
Ok ok...making fun of each other is great and all, but he started this thread to show us his new tarp. Back to HIS tarp. Where are the pics?!
blackbishop351
02-14-2007, 00:02
Ok ok...making fun of each other is great and all, but he started this thread to show us his new tarp. Back to HIS tarp. Where are the pics?!
You're right, and I'm thrilled that more and more people are making these. And especially thrilled that I've been able to help to some degree or another. We definitely need pix though!
The Breeze
02-14-2007, 00:22
just put it up strait as an arrow. tight everywhere but to dark for a picture or you know me im in to pics at night, but its black and you can't see it . it raining and foggy and 34 degrees out well you get it . its just to dark and its black .:rolleyes: :cool: pictures tomorrow :eek: :D
Cool glade it worked out. I think there is a lot of fudge to these projects. I just can't bring myself to do it intensionally, my sewing does it for me.
stoikurt
02-14-2007, 14:00
Did you put binding on the edge or go without?
The Breeze
02-14-2007, 16:34
put edging bios tape around the edge and gross grain tieouts here are the pic.wind was blowing 25 mph when these was took
Just for general information purposes, I got a bug and checked my cat generator against the Excel file Youngblood posted on the Yahoo HammockCamping group. The test edge length and cut-depth were the ones I use - 74 1/2" edge, 1"/ft. cut-in. There was less than 1/16" max difference between my measurement results and his. This error will of course get larger as the edge gets longer.
Anyway, conclusive results - at least for a ~ 6' edge, his spreadsheet works just fine for calculating cat curves. I still prefer my data output method, though :p I also like the peace of mind that comes with knowing nothing's been "fudged"...but that's just the math geek in me.
I also worked up an excel catenary generator a couple years ago - not nearly as easy on the eyes or in use as youngblood's, but uses the same math. I posted it here
---->catenary generator (http://groups.yahoo.com/group/MakeGear/files/)
At the time I tested it by hanging 8 different lengths of chain on my hallway wall and comparing the measured sag against that predicted by the spreadsheet. The predicted and measured curves were very close. You can see the data in the third worksheet "Observed Profiles."
And to get back on topic. . . . nice tarp.