trailranger

I'll be building a simple CAR out of foam and I thought I would ask the Airplane Plane guys on how to do it correctly.

My foam car will not be solid, some areas will be cut out for various reasons including weight reduction. This means I have to cover the car. I am leaning towards white styrene .020" sheeting. It is not available locally, but I know tower carries the sheeting, and I maybe able to order poster board size sheets for $3 a piece. The total project wil need close to 1 sq yard of covering and balsa would be well into the $100 range.

I wanted to use balsa, but felt wood may be too soft to any abbrasion since this is a groud pounder. The top covering must be able to take double stick tape and support holding the weight close to a Compact Disk.

So while everyone is pondering my styrene choice. I would like some help in the internal strength areas. My initial thought was to criss-cross graphite kite spar (.080") as it would weight next to nothing and I could increase the voids. Where my wheels attach, I have a feeling the foam will not be supportive for repeated stresses. Should I use blasa blocks where i need to screw into? 3/4oz Fiberglass reinforcements? Some carbon fiber tow or strips in the area?

Weight is crictical to me, but I don't want this to be real expensive or really fragile.

anyhelp is great.

KC36330

why not just make a mold and lay it out of fiberglass and carbon fiber?? both strong and lightweight, fairly cheap and easy to make.

trailranger

I bought a sample sheet of carbon fiber and the strength weight ratio of a .75mm sheet is not as good untill 1.5mm range. The 2ply .30" carbon sheet weighs more per sq in than lexan and lexan would be stronger. Matter of fact the poster sized carbon sheet came rolled up in a tube . Untill the ply count is higher with thicker sheets, the sheets absorb too much resin making then rather heavy.

Foam by its self is study, but will break beacuse of the low tensile strenght. So if the 22" x 28" x 2" board gets bent, it will break. The car chassis has to remain ridged enough to mount a 21" x 18" solar panel array on top. If the upper deck flexes too much the cells will crack as they are only .20" thick silican crystal. These are not normal solar cells bound to a glass cover like in calculators. These are pure silican crystal designed to be placed into a fixture.. Becuase of weight reasons, there will be no fixure and glass protected cells will be too heavy. Buy laminating Styrene on the surface, it will bond better than lexan and add tensil strength to the surface to keep cells from breaking should I have a minor misshap driving or chassis flex under cornering.

trailranger

I just want to make sure I'm on the right path on the materials becuase I know there are alot of options and have no experience with. This project is a prototype build that I want completed before newyears.

Scorpion Racing

I think KC36330 was speaking of laying up a composite structure using fiberglass and carbon fiber cloth, which is very strong, stiff and lite weight. The carbon plates you have are not stiff or lite enough for what you need. What you buy off a shelf will probably not work too well, as they are just for general use type stuff. If you build the car and make a mold from it, the glass and carbon is the way to go. But, you are talking about a whole set of new skills to learn, hundreds of hours of work on the plug, molds, the first part, and some more money than you may want to spend on it. There are a lot of threads on this process here, if you are willing. But for a one off project, either balsa or foam reinforced with laminated glass cloth and laminating epoxy resin would be the best way. Sorta like building a surf board, the foam is shaped and laminated with cloth and resin to make it strong. One single material is not as strong as a composite (layers of different materials) structure. Shape the foam, cover it with 2 or 3 layers of 3~4 ounce fiberglass cloth and a good quality epoxy (West system is good, pretty cheap and comes in small quanities (105 resin, 206 hardner)) and will be very strong. You will need to keep the resin to glass ratio a close as possiable. The strenght is in the glass being unable to flex, not the resin itself.

Hope this helps some!

KC36330

a single layer of .5oz fiberglass cloth (for smoothness of the finished pull) and then a backer of 6oz carbon/Kevlar will be much lighter, stiffer AND stronger then the same equivalent thickness of lexan

trailranger

Thanks...

Yeah, my idea for the design did come from a surfboard but after that "heavy" carbon fiber panel I didn't want to end up adding 500g worth of expoy to cover a design with a target weight of 1200g.

By the looks of what was suggested, the fabric will be 200g (glass coat, kevlar/graphite under) and the expoy will be 200g??? Leaving 800g left for the guts of the project.

Onto the next question. Do i need to skin my foam board before vaccumm bagging? Are there cheap hand siphion pumps for bagging? The reason I ask is that the foam will have voids for various reasons and that is why I need a covering

Scorpion Racing

Well, if this was my project, I would shape the car out of a foam block and seal it with a layer of 3/4 oz. fiberglass cloth and resin to create a plug. Look at this site http://www.cstsales.com/tutorials.html and follow the ideas for making a plug, mold and parts from them. These tutorials are very good for a reference guide. They cover all the basics.