Saturday, 5 June 2010

Mmmm

Having sewn the main panels of the Starlet together and laying them out on the floor it quickly became apparent that something was wrong. I wasn't expecting that tarp to lay flat on the ground. This would mean it wouldn't pitch properly. After doing the marble trick and sticking some temporary guy lines on it turned out that I was right. Whatever length the guys there's far too much excess material.

Now there's a number of reasons for this. I think the seams may have a cantenary curve in them. I've done straight seams. The material may not stretch as much as sil nylon and the stretch is important in this design. The reduction in size may have something to do with it. Anyway it doesn't work so I'm going to take it to bits and put curved seams in and see what happens.

If anyone has any tips I'd be glad to hear them.

12 comments:

blogpackinglight said...

You might want to drop Ron Bell an email. I'm sure he would give you some tips/advice.

Keith Tilley said...

I've been thinking of making a trailstar-type shelter myself, although I've only seen pictures of real trailstars.
The MLD website says that with all sides pegged down to the ground, the centre should be about 36 inches, so I agree that it doesn't seem right that yours lies flat.
I think that the bottom edges, and maybe the seams, have catenary curves but I don't think that will solve the problem. I think the angles at the top of the sections will have to be smaller. Unfortunately that will make the bottom edges shorter and may not leave you with enough floor area.
Sorry I couldn't be more positive. Maybe someone with a better knowledge of geometry can come up with a solution.

Anonymous said...

You've got some trigonometry to do. You must have made the apical angles 360 divided by 5 degrees (72 degrees). They need to be less than this.

To work out what you need, think of a 3D fifth of the shelter. The shape will consist of four triangles, the two at the sides being identical right angled triangles. The base triangle is isosceles and so is the sloping one. The angle at the tip of the flat, isosceles triangle on the ground will be 72 degrees, as you have shown, but the sloping triangle will be longer and sharper.

Decide what height you want. Decide how far the edges should be from the centre pole. You should then know all of the numbers you need to calculate the size and shape of the sloping triangles (which you can then make out of the material).

A mathematician could probably tell you an easier way to do all this but I'll bet Ron went through quite a few paper models before knowing what he needed to make.

Note, I haven't addressed the catenary issue. The Trailstar seems to have shaping along the bottom edges but not along the seams joining the panels. (I'm going from photographs as I've never seen one in its natural habitat.)

I hope this helps. Best wishes, John

Shed Dweller said...

Thanks for the comments folks. The main problem is that I jumped right into this project without enough thought. I usually mock stuff up with plastic sheeting and gaffer tape, which I will do before trying this one again.

All's not lost though I reckon I can salvage something out of this "thing" that I've put together.

Shed Dweller said...

Keith. I've seen the trailstar up close. but only when it's pitched I'm not sure that there are any curves in the seams or the bottom edge. They're created under tension. I get similar curves in my duo mid and all the seams and edges are straight on that. I need to get hold one one unpitched and then I'll be able to see where I went wrong.

Anonymous said...

Cutting a V out of each panel will give you the shape but I'm not sure about the size. At very least, you've got a groundsheet for your eventual design.

To be honest, I think you are brave to go public with this kind of cock up. I guess all MYOG makers have one or two of these but how many admit it. I just sit in admiration of anyone who can sew or make things out of wood.

Best wishes, John

blogpackinglight said...

It would be good if you could note down the angles and lengths when you modify the design so that others can use the information. A small scale paper mock up sounds a good idea.

Shed Dweller said...

I'll get back onto this project at the end of the week.

John, the cock ups are all part of the learning process. I'm a bit cross with myself because I've already learnt this lesson before - make a model or full scale mock up before committing to sewing. Never mind.

Shap said...

Great project. Try using Google Sketchup. It's free to download and a great way to to do easy 3D drawings from witch you can get all the detail you need. If you cant be bothered email me your sizes and i'll do you a drawing.

Shap

Shed Dweller said...

Hello Shap. Hope you're keeping well. I've tried using sketch up. I'm hopeless with it, really hopeless. Thanks for the offer though. This project has been put on the back burner for a bit. I get in a huff with stuff if it doesn't go right. I'm going to ignore until it says sorry and then, perhaps I'll try again. So I may be in touch in the future. I'm having a good think about 35l backpacks at the moment...

Dereoak said...

Hi Sheddweller,
I think the trailstar is a standard hexagon with one triangle cut out, leaving 5, and the edges sewn together. As a paper model which is very easy to make, the angles seem about right.

Shed Dweller said...

Hi Derek

You may be right, I never thought of such an easy way to work out the triangles. I have now worked them out though and made a template, there is a cat cut curve on each side of the triangle which is essential to the taughtness of the finished structure.

When time allows (in the next couple of years ;-0) I'll unpick the one I attempted and see what turns out.