New Carbon Fiber EarthRoamer

[DzlToy]

Anyone know the real numbers?

While I am neither a structural engineer, nor an expert in composites, I do have some experience and a basic working knowledge. I am also bored at work today and am pretty good with math, so here goes nothing.

In order to do this correctly, you need a LOT of data; data that I do not have. So, we are going to make some assumptions, and that will skew the results some. Estimated data:

Overall Length at Roof Line: 20 feet
Overall Width: 96 inches
Overall Height: 80 inches
Floor on Chassis: 14 feet
Floor on Cabover: 6 feet
Wall Thickness: 2 inches
Core: Structural foam of unknown thickness/density (see below)
Skins: carbon fiber, unknown thickness/density (see below)
Main Side Panels: 14 feet x 80 inches = 26,880 square inches
Chassis Floor Panel: 14 feet x 96 inches = 16,128 square inches
Roof Panel: 20 feet x 96 inches = 23,040 square inches
Cabover Floor Panel: 96 x 72 inches = 6,912 square inches
Cabover Side Panels: 72 inches x 36 inches high = 5,184 square inches
Cabover Front Panel: 96 inches x 36 inches high = 3,456 square inches (chamfer not included)

So, we have a rough estimate of 81,600 square inches of exterior panel area. There will be a slight reduction in interior panel volume, but for simplification, I am going to take 1% off the number above, leaving us 162,384 square inches, 1,127.67 square feet or 106.76 square meters of carbon fiber skin, inside and out. Of course this does not include windows or hatches that may be made from a different material, chamfers and the like.

It is preferred to lay several thin layers of cloth and resin, as opposed to one really thick/heavy layer. So, for this example, we will use three layers of a 3k Twill (2x2) with a weight of 5.9 ounces per yard in 60" width. Because this truck is a hard core rock crawler and will only be taken on the toughest trails, we will skin the panel in a layer of Aramid, as carbon fiber fails catastrophically once its limits are reached. So, we will spec Kevlar 49, in a 2x2 twill, with a mass of 5.3 ounces per yard in a 50" width.

We will assume that proper mixing and bagging procedures are used and that there is little, if any excess resin, resulting in a perfect 50/50 resin to cloth ratio. (This varies by process, product and manufacturer) Pre-preg can be under 30% resin for high $$$$$ parts. Wet layup is about 60% resin. A 50/50 ratio makes the math easy too.

Exterior skins: 81,600 square inches x 3 layers of carbon & epoxy resin = 84 pounds
Exterior skins: 81,600 square inches x 1 layer of Aramid & epoxy resin = 30 pounds
Interior skins: 80,784 square inches x 2 layers of carbon & epoxy resin = 55 pounds
Structural foam core: 3 PPCF Divinycell has a mass of 283 pounds (2" thickness)
Structural foam core: 5 PPCF Divinycell has a mass of 473 pounds (2" thickness)
Total shell weight is estimated at 450 to 640 pounds. This does not include hatches, hinges, windows, in built furniture, attachment hardware or anything else. This is a basic, empty box made with carbon skins (interior and exterior) and structural foam.

If more layers of carbon are used or the resin ratio is higher, the weight will increase. If 12 pound Divinycell is used, the weight will increase. So, for all of the guys building 4,000 pound truck campers, carbon/foam SIPs are your answer.

 

[waveslider]

Good stuff DZL. How do those weight sf numbers compare to the "normal" weight of a fiberglass panel of similar size?

 

[The Artisan]

Good stuff DZL. How do those weight sf numbers compare to the "normal" weight of a fiberglass panel of similar size?

When Dzl helped build my prototype. The panels came out to 1lb per sq ft using 2" 2.5lb eps and .027 phenolic skins
Kevin

 

[DzlToy]

Believe it or not, S1 and S2 glass are not that much heavier than carbon. The advantage comes in being able to use less of the carbon, while retaining or even increasing strength. Vacuum bagging allows the exact (minimum) amount of resin to be used, where wet layup almost always has excess resin, adding weight. FEA software allows layers, thickness and resin to be optimised. I estimated four layers of 5-6 ounce cloth at 50/50. In reality, you could probably save some weight off that, but I am not a composites engineer. Maybe Bill will tell us how close the estimate was.

The other, IMO, majour, weight savings is ditching the Balsa core and going to a structural PVC foam core. I have no way of knowing what products they are, or were using there, unless Bill would care to comment. However, end grain Balsa is about 10 pounds per cubic foot, while Corecell/Divinycell type products can be as light as 2 or 3 pounds per cubic foot and as heavy as 12 PPCF. When you have ~100 cubic feet of foam, those differences add up quickly.

In-built furniture would also be lighter than wood and if constructed as on weight-conscious yachts, would be completely composite, even though it looks like wood or has a wood veneer.

If I had to "guess" I would say that, with proper design of the box and furniture, a completely carbon composite box would be 1000 - 1500 pounds lighter than a fiberglass and Balsa box.

Taking a page out of the motorsport world would allow you to build composite water/fuel tanks, adding rigidity and saving even more weight. Food grade water bladders can be used inside a composite tank to ensure potability. Now, you have eliminated a heavy steel tank, hanging on beefy steel mounting brackets; it is simply integrated into the box, just like a fiberglass live well, storage compartments and seating are integrated into the hull of a bass, pontoon boat or ski boat.

 

[Joe917]

Good to see they have finally ditched the cheap windows.
Earthroamer is a slick looking product that is well marketed.
Poor insulation for a 4 season truck, many with low profile tires???? and why do so many of the used vehicles have such low mileage? Garage queens!
The price is nuts!
Ooooh Carbon vacum, lets add $100k

 

[Zybane]

The difference between carbon cabin and fiberglass cabin is trivial in every way besides the astronomical price.

 

[gregmchugh]

If you want to add more features and stay under the GVWR of the chassis then something has to be removed or made lighter. Cost doesn’t seem to be a prime factor for those buying EarthRoamers so the cost to switch to carbon may not really be much of a factor.

 

[gungriffin]

If you want to add more features and stay under the GVWR of the chassis then something has to be removed or made lighter. Cost doesn’t seem to be a prime factor for those buying EarthRoamers so the cost to switch to carbon may not really be much of a factor.

I agree with this 100%. A used 115k 2014 911 Turbo S with a tune is faster than a new 2019 450k Lamborghini Aventador, but the Aventador buyers want to buy new with the wow factor. Many of the buyers of the Earth Roamer will enjoy having the very best of what is available. This is now where the bar is for the high end semi custom/spec market.

 

[Steve_382]

Well, from this article on Expedition Portal, it's almost 2,000 pounds less. Pretty good really.

The new EarthRoamer LTi was on display, and is without a doubt the best EarthRoamer yet, with a full carbon body and nearly 2,000 pounds less weight.

SEMA Overland Day 2 - Expedition Portal

The 2019 SEMA show coverage continues with day two, and a deeper dive into the south hall and the new products on display from respected manufacturers.

expeditionportal.com

 

[waveslider]

2k pounds is a nontrivial weight loss. Seems you could find that weight in other areas, and without the resultant cost increase, more easily though.

Assuming DZL calcs are correct, and the 2k weight loss isn't exaggerated (unlikely) then that means the fiberglass shell weighs a little under 4k pounds - since the reduction from glass toe CF is about 40%.

 

[adam88]

Well, from this article on Expedition Portal, it's almost 2,000 pounds less. Pretty good really.

The new EarthRoamer LTi was on display, and is without a doubt the best EarthRoamer yet, with a full carbon body and nearly 2,000 pounds less weight.

SEMA Overland Day 2 - Expedition Portal

The 2019 SEMA show coverage continues with day two, and a deeper dive into the south hall and the new products on display from respected manufacturers.

expeditionportal.com

That 2000lbs less includes lithium ion batteries and other weight reduction strategies. I am not sure how much of that is body related.

 

[gregmchugh]

That 2000lbs less includes lithium ion batteries and other weight reduction strategies. I am not sure how much of that is body related.

:Latest post on their Facebook page indicates the carbon body is 1500 lb lighter than the fiberglass one it replaces.

 

[Zybane]

So say a 19,500 lb truck is now 18,000 lb. You gain like 0.5 MPG and ~375lb less contact pressure on the ground per wheel. When you are talking almost 5,000 lbs of weight per wheel (using 50//50 distro just to make it easy), that ~375lb isn't going to make a huge difference in your off-road capability. All for six figure price increase.

Although the newer windows are an improvement. Paying $600K for a small ExVe with plastic Dometic windows in the previous version was/is laughable. I'm surprised they stuck with the old ER layout. Not very good IMO. But ya I guess why not go carbon fiber with a clientele who's money is not object to spend $700K on a beefed up pickup truck with an integrated truck camper in the back.

 

[gregmchugh]

I find it interesting that on one hand there are plenty of people who comment on the high price of an EarthRoamer and on the other hand EarthRoamer seems to have a backlog and a devoted group of owners. While an EarthRoamer might not make sense for many there are enough who think it does make sense to keep them in business. They seem to understand their market and continue to provide a product that satisfies that market. Luckily there are enough other options for just about anyone to find a rig they will like and can afford...

 

[Victorian]

I find it interesting that on one hand there are plenty of people who comment on the high price of an EarthRoamer and on the other hand EarthRoamer seems to have a backlog and a devoted group of owners. While an EarthRoamer might not make sense for many there are enough who think it does make sense to keep them in business. They seem to understand their market and continue to provide a product that satisfies that market. Luckily there are enough other options for just about anyone to find a rig they will like and can afford...

You made a good point. I think the fact that in North America we only have a handful "high end" expo truck builders makes it easy for those builders to charge what they can. In Europe, you have almost hundreds to choose from. Therefore you can select by quality and price. For example: $600.000 will get you a true custom made, very well built Unicat or Krug Vehicle. I have been employed at Unicat and can tell you first hand that absolutely nobody in North America is even coming close to their quality.