CatPerson, I see, thanks.

Well, I really wanted to make it myself, to put effort in it. Not alone, but with some help. Would you suggest not even trying this?

I'm not really concerned about whether should I do it myself or not, but what materials are better to use to make the whole thing sort of solid and movable.

Last edited by fanmaker (2009-07-07 07:20:53)

The main problem with the project you have in mind is the combination of length and support.  The longer the unsupported span is, the weaker it is.  You can have strong PM or lightweight PM, but it's really hard to have both in the size of a car.

Most PMers use chicken wire or something similar for larger creations (think baby elephant).  For the body mass of a baby elephant, one would usually from the basic shape in chicken wire, over mashed chicken wire for support, or it would have garbage bags of crumpled newspapers or bags of styrofoam beads or even sheets cut to shape.  But you want an unobstructed hollow space.

The more curve you have in a span, the more strength you have.  But most cars (VW Beetles excepted) have very little curve over the top.  And the roof won't even be supporting anything but itself!

Then you've got the car floor, a flat (weak) span about 15 feet long that you want to be lightweight AND you want it to support a person.  If you were making such a PM car for a parade float, it would have a plywood floor and other wooden support, with a wire + PM shell.  Even if you used 1x2s on edge, the total weight would be considerable.

This is bad enough, but you want it cut in half lengthwise, thus removing half of your overall support.

It might be possible to do this, but it is waaaaay beyond the scope of my experience.

Moving on to the design of the car... the easiest way to form the shell is over an existing mold.  Try for a M-B-SLR, just for fun... listen to the owner scream when you tell him that you want to wrap it with chicken wire, newspaper and glue. Body armor and running shoes would be appropriate attire.

Last, would be the surface finish.  People are used to seeing smooth, shiny cars.  Finishing PM to a smooth surface is an art and takes a LOT of work for a small surface (think cantaloupe).  For something 15 feet long and 6 feet wide?

Simply put, there are some severe limitations to PM which would take some engineering knowledge to overcome, if it's even possible.  For someone who doesn't even know how PM works (and when it doesn't), I would still say this project would be impossible for you and your friends.

Just because it's simple materials doesn't make it a simple project.

Sorry.

Sue

CatPerson, thanks for explaining your concerns!

Actually, I know how PM works, I just don't have very much experience. But, well, now I see I didn't really think it through.

As for the floor, it may be better to use wood or some kind of a plastic panel?

And I also want it to be cut in half not lenghwise, but widthwise, if you may. So the roof also would have support in the front, in the back and on the side.

Also that's why I wanted to use some kind of solid metallic frame - so that the whole construction wouldn't go wobbly (and I think it wouldn't if all the details are going be attached to each other in a really firm way).

And as for the surface... well, I don't mean to make the car look like it's new and fresh, I wouldn't mind even if it looked just plain props-y. So it shouldn't be beyond possible to paint and varnish it.

I just think that asking some company to do it should be really expensive, and only for one performance it would be unreasonable. But I also wanted to make it myself to put the emphasis on it.

So at least I can try, I think. Hopefully it will turn out pretty good.

I will definitely post a photo of the finished model if it wouldn't embarass me.

Another possibility would be to use foam. For long flat surfaces, sheets of builders foam (the pink stuff sold at home improvement stores for insulation) would support itself nicely. Or even foamboard that is used for school projects and presentations can be used for smaller areas. It is thinner and with a wire armature, can be flexed and bent into almost any shape. Also look into a hot wire foam cutter, they go for about 25.00 and are sooooooo worth it LOL. Then paper strips could be applied over the foam surface to make painting easier, as foam tends to melt when spray paint is used.   The paper covering would also give the finish a nice tuff "shell". For upright supports, cardboard shipping tubes and tubes used to hold carpets are incredibly strong, and come in a variety of sizes. Just be prepared to scrounge ; )
On a project like this, mixed media would be the way to go. Pure papier mache could be used, but the logistics would be daunting.
Good luck with it, it should be an interesting, if not time consuming project!

Nil Desperandum
Surely it's got to be possible?
Do you have the means of cutting and shaping large blocks of polystyrene?   This makes a good base if you want to laminate over it.
Another is corrugated cardboard.  As Sue says, you need 'engineering' principles to get the best strength.  If you stick sheets of corrugated cardboard together it becomes very strong and can be carved and rasped into shape.   Laminate over it with strong (kraft) paper in several layers.   This would be plenty strong enough to sit on.
If you make a box section (like a girder) in strong cardboard, that also is strong.
Another idea, take two toilet roll tubes, squeeze one into a figure of eight cross section and push it into the other.  Then try squashing it by pressing the ends in!

Sheets of thinner card (large cereal packets) laminated into shapes, hold curves quite well, especially if you put a length of strong wire along the edge, held with bits of masking tape.
Let us know how you get on and whether you find any new techniques for achieving it!
DavidO