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half pyramid – any math whizzes out there
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Home › Forums › Gear Forums › Make Your Own Gear › half pyramid – any math whizzes out there
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Sep 6, 2006 at 1:40 pm #1362519
Very cool find. Looks very similar.
Sep 6, 2006 at 2:00 pm #1362520It looks a little like mine.
Sep 6, 2006 at 2:23 pm #1362521AnonymousInactiveJosh
You’re right the Penta Tent it is a cool design!
I especially like the bug shelter base and the way they incorporated a canopy on to the tarp. Nice options for keeping the mosquitoes out and even more protection then the typical 1/2 Pyramid / Alpha-mid from wind blown rain.
Sep 6, 2006 at 2:56 pm #1362525Someone @ snowpeak hacked Bill’s brain!
Sep 6, 2006 at 7:45 pm #1362540“Someone @ snowpeak hacked Bill’s brain!”
No, the Penta Tarp has been around quite a while now. I’ve had mine since 2001. The inner tent and removeable awning are new, however, only coming out a year ago.
The Penta was originally designed for kayakers camping on beaches (it even comes with a separate sleeve to accommodate a paddle for use as a pole). It is HUGE! However, the shape allows for all sorts of configurations, from a two meter tall pyramid with one side missing, to a low, wide wing that can sleep four, to a tent awning like Bill’s, to a bat-like A-frame. My only gripes with the design are that it has no provision for a front door and the catenary cut sides are a little too deep. The material is a 75D polyester (doesn’t stretch) impregnated with silicon on one side and the other side covered with polyurethane. It’s very strong (much stronger than the usual silnylon), but also quite heavy.
I liked the design so much that I used the pattern to design my own Lunar-Solo-like tent about a year before the Lunar Solo came out, cutting down the dimensions for one person, making the catenary sides shallower, and adding doors to the open side of the pyramid. Alas, it is still too big, so one day when I have the time I want to cut it down still further.
The original Penta itself I have few occasions to actually use. It is just too big and heavy for backpacking, and I don’t go camping with enough people usually to justiify bringing it on my trips when I am not alone. If Snow Peak would make a smaller version they would have a wonderfully versatile and strong tarp on their hands.
Sep 7, 2006 at 9:39 am #1362570The tent combo thing is what is new to me.
Sep 10, 2006 at 9:00 pm #1362790here’s my off the top of my head calcs.
Finished diameter will be:
D = Length of curved floor edge / Pi
L = ( Length of curved floor = 9 x PI if using full width of sheet and 18 ft length)Height will be:
H = ((9^2 – (D/2)^2)^.5
Ok, simplified formula, or rather, not so many steps:
R = Radius (9′ in this case)
A = Angle of arc of flattened cone (180 degrees in this case)
Height = (R^2 – (2R * A/360)^2)^.5
Diameter of raised cone will be:
D = 2R*A/360H = 7.79′
D = 9′You could make a pyramid tent too, with corner to corner length being 9′, and wall to wall length being a little over 6′.
Well, both of these instances give no slop for attaching the wall edges. So you’ve have to figure an inch in there I guess.
Dwight
Sep 28, 2006 at 11:57 am #1363817Ok, through the cumulative efforts of several people on here, I’ve pulled together a new version of the spreadsheet and charts.
This one calcs the layout points for the half-pyramid shell itself, and also shows the layout points for the doors, given a specified width of a vestibule.
If anyone is interested in getting a copy, and checking my math certainly, email me at [email protected].
This is adapted from my original version where the fabric width, tent width, and tent height are specified. I’ve added the specification of the vestibule width.
Rich had a spreadsheet that allowed you to approach it from a few different directions regarding specified dimensions. Feel free to take what I’ve done and add it to Rich’s spreadsheet if you so desire.
Dwight
Oct 5, 2006 at 10:54 pm #1364376Hi Miguel
> The material is a 75D polyester (doesn’t stretch) impregnated with silicon on one side and the other side covered with polyurethane. It’s very strong (much stronger than the usual silnylon), but also quite heavy.
Source of this material?
Cheers
[email protected]Oct 6, 2006 at 1:20 am #1364382Source of this material?
Hi Roger,
Er, when you say “source” do you mean where was material manufactured, or where did I get this information?
The information was written right on the package that came with the tarp when I bought it. I still have the package because the diagram on the front helped me when I design the pattern for a silnylon copy I made. You can also find the information here (Snow Peak’s official site… though it’s in Japanese, if you scroll down you can see “75D” and next to it, in Japanese, “polyester taffeta”) and here (the unofficial, but recognized site of people devoted to the Penta here in Japan. Again you can see the “75D” and next to it “polyester taffeta”).
If you’re asking where the fabric was manufactured, I haven’t the foggiest. Contact the people on the Snow Peak or Penta e-Club sites. Someone is bound to speak English.
Oct 6, 2006 at 1:51 am #1364383Just took a more careful look at the information on the Snow Peak s ite. The material doesn’t have silicon on one side, but rather teflon. The other side does have the PU coating. My mistake.
Oct 7, 2006 at 3:11 am #1364453Hi Miguel
Yes, I was mainly interested in where to get the fabric itself. But I find companies do not like telling you this.
I had a look at the Penta web site. I am slightly boggled that you could find enough people sufficiently crazy about an odd-shaped bit of fabric to create a web site!
Ah well. I’m off in the morning for a week+ walking, so I will have to leave it until I get back.
Thanks anyhow for the URLs.
CheersOct 18, 2006 at 1:42 pm #1365107Well I made a half pyramid without all the fancy math which does me in, but when the flat side faces the wind, forget it. It just gets blown away. I had fun making it out of the most vibrant colors I could find, but it has never made it out of my backyard and probably never will.
Go with a full pyramid as found at golite or owareusa.
Oct 18, 2006 at 3:33 pm #1365117Did you sew a tie-out point in the center of the large side of fabric? I would presume that having a tie-out located there would stand a fighting chance against most winds.
Oct 18, 2006 at 5:59 pm #1365125Do you mean the vertical side, where the door is, is not good in the wind?
I was afraid of that, and figured in a vestibule on it. In this photo, one door of the vestibule is missing, so show the interior.
Haven’t built it yet though. You’re ahead of me.
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