CarBEN EV5 Full Sized Prototype Construction - 5 Seat Electric Car From Scratch

[aerohead]

Originally Posted by freebeard

That's getting pretty close to the half-circular section of a half-body of revolution. And it's box cavity-ish.

Koenig-Fachsenfeld and Kamm would be grinning from ear to ear.

[NeilBlanchard]

The wood glue soaks right into the fiberglass fabric, quick as you like. I'll be testing these samples for strength.

[NeilBlanchard]

This discussion is going to be invaluable - bouncing ideas off of each other gets us all thinking.

I'll try to finish up the rest of the test pieces today. We are actually getting rain today (first time in about a month!) so dry time will be slowed considerably.

Someone suggested a method for testing the strength of the fiberglass: narrowing the pieces until they fail - I don't need to be too precise, but I do need to get a feel for how this stuff works. I like the 8 loom fabric much better than the regular woven stuff. The 3oz E-glass is 8 loom, but it is easily buckled and forms bubbles. I'll use it for things like the diffuser fins on the underside, etc. It softens up in the wet glue and it will hug into tight corners pretty well. So with the E-glass, I'll probably end up using mostly the 8.9oz 8 loom fabric - it is available in a much wider roll than the others and it also costs a lot less.

If the S-glass is significantly stronger, then I'll use it on the underside of the chassis and on the areas where the subframes bear - though obviously those areas will need metal reinforcing plates and sleeves, too. The inside of the front and sides around the passengers, maybe too?

Vacuum bagging is probably not a possibility on this first iteration. My work space is very cramped and crude and I don't have space for a pump/compressor. And until I get some crowd funding, I can't think about building onto my garage, or any big tool purchases. I still need to finish shaping the left side of the car and the hatch door needs some attention - and hinges for the hatch door are going to be needed.

I need to buy the windshield and the wiper arm assemblies, to get them fitted.

So far, the edges of the fabric are the only part that sheds fibers. And the roughened foam really causes havoc with the surface on all but the 10oz regular weave E-glass. It is rather stiff compared to the 8 loom fabrics; which "drape" and conform much more readily. So useful things and more challenging things about the fabrics I've tried so far.

[Rokeby]

Neil,

I'm not convinced that your plans to use a wood glue/fiberglass laminate is a good idea. This from my history as a professional boat builder with experiences in composite construction from 65 ft fishing vessels to small skiffs, canoes and kayaks. It is widely held that boat builders are a conservative bunch. Well, I've been one of them, and perhaps as a result I'm over cautious. So be it. Here are my thoughts.

Fiberglass composite construction has been around since the early 1950s. In the time since there have been many (r)evolutions in the types of fabric used; woven and non woven; symmetrical and non symmetrical; different materials; glass, aramid, carbon fiber, etc. But through it all the choice of resins has been severely limited, and for the most part survived the test of time. Almost without exception, and at least as far as availability to amateur builders, the preferred resins are epoxy and polyester. The combined system of glass cloth - of whatever physical characteristics - and epoxy/polyester resin is highly refined with a high degree of repeatable success.

I take it that the primary reason for your choice of wood glue is cost. I feel that given wood glue's unproven record, its use is a false economy. As between epoxy and polyester resins, polyester is by far the less expensive. I have never encouraged amateur builders to use polyester resins due to its greater health risks. However, in your case I would urge you to consider it, being mindful of personal safety concerns which might include full coverage (Tyvec suit, gloves) and airmask with air supplied from outside the working space.

My specific concerns about the unproven use of wood glue are many. They include:
* possible brittleness of the dried wood glue
* adherence of the glue to the 'glass cloth used
* achieving a near 1-1 cloth/glue mix (1-1 by weight is the ideal epoxy-polyester'cloth ratio for max strength, lowest cost. Dunno if it's the same for wood glue.
* full drying of the glue. The desired thickness of wood glue in a joint is down around one-thousandth of an inch, much of the water in the glue is taken up by the wood, the rest is dissipated by evaporation. Also, ideal clamping pressure is around 100 psi. In your case, the relatively thick glue layers - there will be no clamping pressure - can dry by evaporation only. A possible comparison is vinyl, water based, paint which has a much greater film thickness than alkyd, oil based , paints. Water based paints take a full 30 days to completely dry.
* resistance to cyclical loading. This is critical for the laminate in way of the attachment of the suspension bits, critical areas. This can only be verified by actual testing. It's not completely relevant here, but aircraft parts/joints are vibration tested under load to millions of cycles.
* final stiffness of the structure. I'm not confident that layup schedules that would provide adequate stiffness with epoxy/polyester will do so with wood glue. This can only be verified with side by side testing.

I wish you the greatest success with your project. To achieve the success you are working so hard to achieve, I recommend you take the time to fully reconsider your choice here, including what testing is in order. It wouldn't surprise me that a comprehensive testing program will take 3 or 4 months to research, devise and implement.

Rokeby

[NeilBlanchard]

The main reasons I using waterproof carpenter's glue is: no nasty vapors, no mixing, cleans up with water, and it has a chance on being biodegradable. It is not cheap at ~$33 gallon, but it is less expensive than epoxy.

I'd have to use epoxy, given that I am using the XPS extruded polystyrene foam.

From what I have seen using this Titebond III glue over the past year or so on the XPS foam is that it remains quite flexible even when it is much thicker than it will be on the fiberglass. Edit: as you flex a thick piece of this glue, it softens somewhat, and after repeated extreme bending (well over 90 degrees) it then gently breaks. It is definitely not brittle.

The bonding with the fiberglass fabric is much easier/better than I had thought. I'll post pictures of my sample pieces soon. Drying on the surface will be fine - when there was too much glue between the layers of foam, the drying took days/weeks, but most of the time it was dry quickly - on dry warm days.

Today is near 100% humidity, so drying to lose surface tackiness is about 12 hours, and much longer for thorough drying.

Worst case with this chassis is that it becomes a male plug to make molds from.

[knochenhauer]

Originally Posted by NeilBlanchard

Can anyone think of a modern front wheel drive car that has double 'A' arm front suspension, that could be found used?

I think Factory Five Racing has a suspension kit that might fit your needs. They also have some pretty slick cars...

https://www.factoryfive.com/kits/mk4-roadster/design/

[Galane]

Have a look at

http://www.youtube.com/watch?v=QzVVqXxbGSA

for the rear suspension. Would also need hydraulic brakes and a way to connect dampers.

They make them with 7 different angles for ride height. Capacities from 600 to 12,000 pounds.

[Galane]

Have a look at

http://www.youtube.com/watch?v=QzVVqXxbGSA

for the rear suspension. Would also need hydraulic brakes and a way to connect dampers.

They make them with 7 different angles for ride height. Capacities from 600 to 12,000 pounds.

[freebeard]

^^Thanks for that. I'm working on a design for a teardrop trailer and they have capacities down to 600lb.

Dampers aren't needed with rubber in torsion.

[stankoprowski]

Neil,

A question. You have decided that you don't need the structural properties of polyester/vinylester/epoxy. Have you considered alternate cloths, like hemp, bamboo or whatever?

Stan

[QUOTE=Rokeby;381696]Neil,

I'm not convinced that your plans to use a wood glue/fiberglass laminate is a good idea. This from my history as a professional boat builder with experiences in composite construction from 65 ft fishing vessels to small skiffs, canoes and kayaks. It is widely held that boat builders are a conservative bunch. Well, I've been one of them, and perhaps as a result I'm over cautious. So be it. Here are my thoughts.

<snip>