rotomoulding

[motas]

Hey guys anyone ever thought of rotomoulding a camper? I had a tour of a factory yesterday for an unrelated product and got me interested. One thing I am familiar with is the water filled barriers which are rotomolded plastic and pretty dam tough. The plastic is really quiet flexible and tough and theres a few different types to choose from and can pick various colours. I doubt it'd be very easy to puncture. It also doesn't crack so no need to make a special mounting subprime just bolt it straight to the chassis and let it flex. Since it is naturally a hollow shape the inside could be filled with insulating foam which would also add some strength. It would also be easy to mold in seats and a bed among other things.
The molds are reasonably expensive however. You can make them yourself out of sheet steel for basic shapes like a camper and just pay them to spin it though which would save a lot of cost. The plastic isn't overly cheap though.
The disadvantages I could think of would be that all attachment points need to be moulded in with inserts and the design has to be finalised in the design stage and cannot be changed. It is also difficult to repair properly although it could easily be patched up on the road. I am also unsure about the weight of it though it could be just as heavy as other methods or heavier. But since the mold is already made it would be very cheap to have another one made identical in the case of a write off or if someone else wanted one. And the mold is relatively easy to modify.
Any thoughts on this guys?
Cheers.

 

[mhiscox]

Yeah, it seems like a great idea, and I was really hot to try and make this work several years ago. And I did some research which, as best I can remember, matches your assessment of the strengths and weaknesses. There were enough big rotomolded tanks to make me think that the size could be handled, though getting one that was non-roundish and looked reasonable seemed iffy.

As you point out, though, the cost of the mold means that there's no real way to test out this concept at a reasonable cost. It appears that, like a lot of things, the first one costs a fortune while the thousandth (or even hundredth) one is pretty darn cheap.

There are some rotomolded trailers readily available; check here, for example:

http://www.bestbuydealer.com/

They're a good deal less "overlanding" than I'd have hope for, though.

And I think the U-Haul Sport Trailer has a rotomolded container,

but I don't think that's going to help us either.

Short of a rotomolding factory offering us a group buy on a camper shell, I don't know how we can proceed on this. There's something to the idea, though, methinks.

 

[Haf-E]

Rotomolding is great for curved surfaces but any flat surfaces look terrible - lots of wobble. Also the plastic isn't great to paint/finish. Could be an option for a small camper / trailer -as long as the look wasn't that important. Would be hard to insulate unless a double shell idea was used - one inside of the other some how.

I think if it was worth doing someone like Casita trailers would use it instead of fiberglass.

 

[quickfarms]

These boats are molded plastic

http://www.triumphboats.com/boats.php

You should check them out. The thing about a boat is that most surfaces have some curvature to them. The exception is the floor.

Check them out in person

 

[motas]

Yeah, it seems like a great idea, and I was really hot to try and make this work several years ago. And I did some research which, as best I can remember, matches your assessment of the strengths and weaknesses. There were enough big rotomolded tanks to make me think that the size could be handled, though getting one that was non-roundish and looked reasonable seemed iffy.

As you point out, though, the cost of the mold means that there's no real way to test out this concept at a reasonable cost. It appears that, like a lot of things, the first one costs a fortune while the thousandth (or even hundredth) one is pretty darn cheap.

There are some rotomolded trailers readily available; check here, for example:

http://www.bestbuydealer.com/

They're a good deal less "overlanding" than I'd have hope for, though.

And I think the U-Haul Sport Trailer has a rotomolded container,

but I don't think that's going to help us either.

Short of a rotomolding factory offering us a group buy on a camper shell, I don't know how we can proceed on this. There's something to the idea, though, methinks.

I was talking to the owner there about the molds and it is very expensive to have one milled or cast but they can be made of sheet metal yourself fairly easily and cheaply (although labor intensive), so my guess is the mold would cost about what a camper made of steel would cost which isn't all that much. Adding the cost of the plastic and your probably about where an aluminium one off camper would cost. And the design of the mould can be fairly simply changed with some cutting and welding plus the prototype can simply be recycled.

Rotomolding is great for curved surfaces but any flat surfaces look terrible - lots of wobble. Also the plastic isn't great to paint/finish. Could be an option for a small camper / trailer -as long as the look wasn't that important. Would be hard to insulate unless a double shell idea was used - one inside of the other some how.

I think if it was worth doing someone like Casita trailers would use it instead of fiberglass.

But curved surfaces are much stronger and more aerodynamic so although it has to be taken into consideration it isnt really a problem. My camper will be approx 2.5x1.5x1.1m and by the time theres windows, doors, storage etc there probably wouldnt be that much flat surfaces. Although I would like to have it painted which may be a problem, my brother is a painter so i may talk to him and see, i know there is a plastic additive for paint which allows it to flex more and also specific plastic primers. My plan for double shell was similar to soenkes camper. A top C shape overlapping a bottom C shape which extends to increase height. Then the inside of these could be filled with foam very easily.

 

[Ozarker]

You could do a boxier shape, but doing one that had say 6 1/2 feet of headroom means the machinery would be huge, not many machines are capable of spinning a 3/4 of a ton that size. You could certainly rotomold furniture sections, rounded cabinets with cubby holes might be cool. But as mentioned, even if you found a roto machine large enough the cost for a one off project would be much more than its alternative choice, like aluminum. I'd think that a machine large enough would be expensive, when machines cost bunches they need to be running to payoff. That means whoever owns it has product turning out and to do a one off project or even several custom jobs, that interrupts the production which costs more money. You'd almost have to find a business going out of business that had a machine or a company that is off line for some time for some other reason to get a one off project or even a few made. Unlikely, I'd say. If you could find one, I bet it would cost at least 4 times their costs to tool up, run the product, tear down, then re-tool back. Now, if we could get oh, guessing, a quarter to half million to have the machinery to do an 8x7/12/14' boxy shape, you'd have it made. But if you had that kind of money for a camper I'd rather have a Kevlar camper. For that kind of money I might be able to have a Kevlar body shell duplicated for my vehicle and get rid of the metal body.

 

[motas]

Firstly mine would not be 6.5 feet tall due to the size of the car, but it is very possible, the tanks they rotomold are huge compared to a small sized camper and well over 6.5 feet tall. Also what was interesting about this company is they can put any mold in with any other on the line and nothing is interrupted and they dont stop the machine to switch molds. So there are plenty of parts they produce at low quantity at no extra cost. In fact from what i saw they generally don't have the same mold on for very long. So the beauty of it is other than the mold it costs the same for 1 as it does for 100. You pay for the plastic, the labour to swap the molds (about 10 mins) and the 30 mins it takes to spin it in the heater and another 30 minutes to spin it while it cools.

 

[Ozarker]

Motas, It's been a few years since I looked into rotomolding a catamaran, that's what I found. Sounds like you have a good opportunity if they have that capacity. Draw it up and get a bid!

What I also found was that there are several options in materials, most don't like common glues, stuff like liquid nail or monkey grip, contractor adhesives. Might check on that and consider how you'd insulate the camper. They can also thicken areas such as building up a door jam or hatch. Might ask about internal supports being molded in or using ribs to stiffen it up.

Only way to really know is to price it out and see. And, think of the parts you could have, water tank, molded kitchen, shower, holding tank, cabinets, it could be really nice.

 

[motas]

do you know if there were any suitable materials which can be glued? I think that is the biggest issue with rotomolding is it cant be edited. if there were suitable glues or epoxies you could cut and fill holes and add cabinets and such. without that it is a very limiting construction option.
You could make most of the cabinets and such out of rotomolding as seperate pieces as you say which would have advantages like the whole thing being one strength and flexing together. but again there needs to be a way to attach them together because all this cant be molded in.

 

[Ozarker]

Yes, If it's a one piece camper it would be with separate pieces, bolted together. I know this started as a rotomolding project question, but vacuum bagging polymers/glass might be a better solution as you can mold a bottom 1/2 and top and form interior parts as they do for boats. They would be bolted together just as the deck is bolted to a hull.

I like the overall idea, you can turn out a very nice unit, just add $$$$$! LOL

 

[motas]

Vacuum bagging would also be a very good process. My concern with using fiberglass though would be the lack of flex. I would prefer not to have the added height and weight of a pivoting subframe and leave the camper to flex with the chassis. But fiberglass, carbon fibre, aluminium all do not cope well with cyclical loads like this. This basically leaves a plastic or steel. Steel is unfortunately fairly heavy which I why I was looking at plastics. But at this point nothing seems to fit what I would really like. Does anyone know of an option I havent thought of? I would like it light weight flexible and resistant to puncturing and dinting.
cheers.

 

[Ozarker]

Everything s a tradeoff. If you need light, repairable, resistant to puncture, denting and rips sounds like you have one choice, carbon fiber, the tradeoff is $$$$. Plastics have issues too. Sitting in the sun some will deform, warp and lose resistance to damage, you can research that further by looking at canoes and kayaks. The better materials are proprietary and you won't get the raw goods I'd bet, like Rolex. Many of the plastics used on boats have further tradeoffs, the may be puncture resistant but they are difficult to patch if they are damaged. Carbon fiber is tough stuff, light and repairable.

Plastics might present some construction issues too, need to use specific glues, if you can find any that works on some materials, but that glue may not work well with other materials like foam board, metal or wood, trying to insulate a wall or ceiling. If you have "through hull" openings with screws, you have water issues. There are all kinds of washers and gasket materials to prevent leaking, bottom line is that it's an opening and it can leak, ask anyone with boat with a cabin. It's a maintenance issue.

Want a roof rack? Another hull penetration, again, look to boats for techniques and glass and plastics can have stress point issues.

Plastics will sweat, insulation properties aren't the best.

I like the idea, don't want to rain on the parade but I'd have to ask.....these plastics and compounds have been around for what, 25, 30, some for 50 years. It's not like the camping industry isn't aware of plastics. There must be a reason why plastics are not being used for camper bodies. It would be easy to fabricate, it would be cheaper and you could have some cool shapes, so why aren't plastics already used? Over my years I have found that most of my ideas have already been thought of by someone else at sometime.

My last crazy idea was a foldable inflatable boat the used a trailer frame that could be pulled by a medium size dual sport bike. The bike could fit on the boat, go floating down the river and when you're done, pack it up and ride home. No shuttle needed! Well, after a couple years of messing about, the challenge is greater than one would think. I bought a Transalp to use and a blinding flash of the obvious hit me, how do you fab a trailer hitch on a dual sport swing arm suspension? It can be done, but it sure would be ugly and fixing a flat would be harder too. Poor proper planning! Just saying, ideas are often just that, an idea. I now understand why we can't buy boats that can be pulled by motorcycles and used in that manner. I think if it was a great option someone would be building them that way.

 

[motas]

My needs/wants are a bit different to most. Am I wrong in thinking that carbon fibre will crack under cyclical loads? Due to very limited height I am trying to get away without a subframe but the chassis flexes a lot and need something that will flex with it without breaking, plus that would allow me to bolt it to the body and replace the hard top and give me heaps more room. I don't want/need a roof rack so it only needs to hold itself up and take the forces of off road driving and in the terrain here will probably get rubbed into banks and trees etc which is why I want to keep it as low as the roof of the car or very close and as thin as i can get it. The weather in australia also means i dont need a lot of insulation, its a nice bonus but not required like some areas of the world. Ive slept basically everywhere in australia in a canvas tent and an okay sleeping bag and mat without issue. The coldest places would barely see -10c and the hottest is generally in the daytime where I dont plan to be in it much. But locally where I will mostly be driving it I really just want to get out of the rain.

By no means are you raining on my parade I put this up as a discussion not as a plan and was hoping someone would point out the problems before i found out the hard way. It was simply an idea that occurred to me while visiting the factory for an unrelated product, not a plan. But I disagree that most ideas have already been thought of. Sure there are always issues and challenges but there are still some very innovative products which in hindsight seem really obvious being released today.

I know the cost of tooling is a huge expense, our small part about 1000x500x50mm is going to cost quite a few thousand to get a wooden sealed blank then another couple of thousand for each mold to be cast from the blank. The other to options are sheetmetal or milled molds. Milled molds would be impractical for obvious reasons. The sheet metal molds dont have a great surface finish and would need a lot of labor to look any good for each one made. Also sheetmetal molds which will last for typically a few thousand runs need to be built very well to avoid warping issues. And besides the cost of making them it needs to be stored when not in use. And the other problem is that any changes as the company goes on would be very expensive compared to most materials. And for a fairly niche market with relatively small companies producing them I can see why no one has done it before even getting into whether the material/process is suitable. Obviously for a single build some of these problems remain but some go away. The labor of me to neaten up one of these is not a big deal. And the mold only has to last one spin and will never really be adjusted.

But the material issues are there regardless of how many are produced. For the ones you mentioned I would mount threaded bungs in the mold every 500mm or whatever in places i may want to mount things which could then be filled in. If it is needed in the future drill and tap it and there is a strong sealed hole to use for mounting. For insulation I would use a double skin construction and fill it with expanding foam. But yes the warping and deforming problems arent really fixable other than stiffening the shape somewhat. It is still hard to patch properly. At this point I don't think its the right path for me but I do believe it is a viable option.

At this point I am going to draw up some steel designs see if a high tensile steel can be made light enough. My work uses a fabrication company which has CNC laser cutting and CNC sheet bending and the accuracy and shapes they make is incredible. I think I will have a play with carbon and fiberglass designs too and see how they compare. Solidworks is an amazing tool for it and with the material properties will tell me the forces it can take and the weight in just a few minutes. I have a long time to research though so hopefully i find a suitable material at some point.
Cheers.

 

[Ozarker]

Are you trying to go commercial? Sounds like you want a prototype. If so, you need to consider the marketing side, things that are extremely different than what your target market is accustom to is hard to sell, the public wants a track record and familiar materials. Electric cars should be all over the road, while they are simple, nice, some are very fast, the barrier is the price and the bugs, it takes a long time for market acceptance. Design is in the eye of the beholder and functionality. More common materials in a better design can enter the market much easier. All IMO,

 

[motas]

no definitely not a commercial venture. I just have a lot of time on my hands to consider these things being a student. I forgot to mention that I think a lot of potential customers would be put off by being plastic. I know before I saw some of the things made that I was fairly against plastics. your dead on though people like what they know works. I know id be very wary of buying an electric car it just doesnt sound right. I work at a road safety company drawing designs and theyre developing a completely irrelevant product which is why I was there to understand the process. They used to have water filled barriers made there though and they are surprisingly strong I couldnt believe it. we ran an empty one over in an off road buggy during a race and it just popped back to shape.
I think people tend to get stuck in their ways and old school materials just keep getting used, I know I was steel all the way not long ago. I had an 8mm steel bull bar on a jeep just cause it was cheap and I could. dont get me wrong all materials have their place but im trying not to just use whats been done forever because its what was available and broaden my knowledge a bit. and I tend to get a lot of random ideas as im sure many people here do.