Foamie damage

[GPW]

Tony makes a Great argument for Stiffness !!! … open boxes just aren’t that strong … Seems like a Design question eh …

Just playing now with an old shoebox , open isn’t very strong allowing flexing , closed with lid seems to be Very strong as long as the lid is secured tight in place … Hmmm ???

[dancam]

Woah! I thought I would get emails if there were replies! Sorry for not responding sooner, I will reply to everyone, it just might take me a couple days

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[dancam]

Do you guys have any suggestions or tips for anyone who wants to make a pop-up foamie in the future?

That open-box design as you know, is a problem. But if anything would work, fiberglass/epoxy instead of PMF. You could reinforce the stress points with extra glass.

But hey, you guys had a grand adventure in it.

Tony

We did have a grand adventure! Fiberglass over the lifting points on the inside would probably help, does it stick to paint or would that have to be done before painting?

Big plywood gussets in the corners. Like 2x2 feet, glued to the roof and screwed to the embedded wood framing. Repair the exterior with canvas patches.

I see from other comments that my lifting points are a problem. This plywood on the inside wouldnt work for me now unfortunatly because I have no gap between the top of the cylinders when they are down and the ceiling. For someone else building it different would be a better idea, I will mention how I would do it different in reply to another comment lower down, but thanks!

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[dancam]

Hey Dan , maybe we can all put on our thinking caps and help out with your dilemma ..??? For instance … Do you think the wood bracing made it too rigid when it might have done better if having more flexible … ??? We saw those videos of Rigid trailers coming apart , when a little flexing would have saved them … ( Just a thought )

Do you think the wood bracing made it too rigid...

I'll argue that it's the flexing that caused the failure. It wouldn't have happened if it wasn't made from two open boxes which of course wasn't an option. The only way to make something like that work is to prevent flexing. Stiffen it up.

Torsion boxes are strong because they don't flex.

Tony

On my build I think the problem was in-between. The damage from the lengthwise flexing was caused by it having too much mass because of the wood yet not being strong enough to not flex.
If it was lighter (foam with no wood) it would not have flexed nearly so much since there is less mass-however that design wouldnt have worked for me.
If I had used something heavier but with more rigidity/weight it would have been fine as well.
Again, i think my joints in the wood were a major problem as well. I screwed them, used angle brackets and glued all the joints but there was just too much flex.
Also a stiffer frame would have gone a long ways, my wooden open boxes were trying to dampen the flexing of the frame which has a lot of mass especially with that water tank bolted to it.

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[dancam]

Yes, the lifting points' loads must be well distributed IMO with a rigid metal profile.

The way the cracking radiates from the lifting points makes it very likely that was the cause?

I did not realize this until you said it. All the cracking at the lift points would be caused by lifting, not flex while driving down the road!

Watching the video of the top lifting, I wonder if the air cylinders on four corners isn't part of the flexing problem. It looked pretty easy to rack the top from unequal lifting.

It should be possible to have it securely clamped in the down position to eliminate flexing it that's a problem. Maybe a removable brace to tie the back together while traveling and set/take down.

As far as clamping it down while travelling- i will upload a little video later and show that, but i did secure the back down so that it wouldnt flex in and out while driving.

Yes, the lifting points' loads must be well distributed IMO with a rigid metal profile.
.......?

Or a mechanism that guarantees all four corners lift together like the cable system in a pop up.

So, with the lifting... we had loads of problems with that. These air cylinders were version 5 and were completed 3 days before we left I believe. First versions leaked bad but I had glued them all togeather and had to buy and make everything new for the next versions. Abs and pvc pipe is very uneven on the inside and my seals would seal for 3 inches of travel, leak for 2 inches, be too tight for an inch, then slide nice and seal, then leak too much to lift.... This last time I used some fancy seal and dry fit and tested everything and it worked perfectly, no leaks at all. Then I took everything apart and glued it all togeather, but i believe I damaged the seals on 2 cylinders when installing them- the ends of the pipe were pretty sharp. They leaked the first time I tried them.
My air compressor is the biggest 12v compressor canadian tire sold. 4 piston, 40 amp draw. Moves a lot of air for a 12v compressor but not enough for my leaks.
The top would go up unevenly because of the leaks. A lot of times it would get half way up, then one piston would suddenly leak and it would come crashing down. Twice my wife let all the air out with it up and it crashed down right from the top. Quite a few times we had accidents when lowering and it would get jammed, all the air would leak out before I got it unjammed and then it would crash down the last foot or 2ft.
3 times we couldnt get it lifted with the air so we asked neighbouring campers to help us lift it. One time the guys we asked were drunk and really slammed it around. The second time the people we asked had no concept of how light it was and nearly threw it right off the top after jamming it 50 times while lifting....
That top half has been through a lot...
It also doesnt lift evenly because of the rear overhang. The rear cylinders have to lift more than the front and they are the same size

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[dancam]

Yes, the lifting points' loads must be well distributed IMO with a rigid metal profile.
.......?

Or a mechanism that guarantees all four corners lift together like the cable system in a pop up.

Sorry, but I dis-agree with both you. Most of the lifts are done with spring loaded arms and no way are they 'balanced'. Look at the RTT's and see how they work. Granted most are angle lifts, yet some are still full lifts. No way can you release a clamp and even think it will go up equally. I don't see that as the issue here.

This lift-top looks like a 50/50 lift. Most are 75/25 or less. That makes them work well. With this, we're far beyond that and what can we recommend as a solution?

He has a pneumatic lift. My thought is it's under powered and requires regulators to balance the lift. How to do that with what he has? Come on folks.. We have a ME here that can assist in a add-on for him?

What do you mean by a 50/50 or 75/25 lift?
Pistons are fine-they only require 15 or 20psi to lift this top, its my compressor not having enough flow to build pressure over the leaks that is the major issue.

In this case (lifting a box that fits over another) lifting the box straight, without racking is important. RTTs and most pop ups have soft sides so lifting evenly is less important.

In terms of something to fix the problem (assuming the problem is uneven lift) maybe a cable system at the corners that constrains the top as you lift it to keep it straight. So, pressurize the pistons and slowly crank out the cables to allow the pistons to lift. Crank down against some air pressure to lower.

The cable system sounds complicated but that would work to keep it even going up. The uneven problem though is always from it dropping while trying to lift because of an air pressure loss or from a sudden air loss while lowering. I have gotten a lot better at the lifting, but the lowering is still an issue.

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[dancam]

How about different door latches............. Cam locks.
Like a double hung window latch in design to hold things
stable?

Watching the video of the top lifting, I wonder if the air cylinders on four corners isn't part of the flexing problem. It looked pretty easy to rack the top from unequal lifting.

It should be possible to have it securely clamped in the down position to eliminate flexing it that's a problem. Maybe a removable brace to tie the back together while traveling and set/take down.

Here is what I did to keep the rear from flexing side to side while travelling. I made a piece of aluminum for the door to fit a slot on the doorjamb.


Then when its down I use a ratchet strap to keep the sides togeather also and the trailer box tight to the gaskets on the frame. The ratchet strap goes from the circled loop under the trailer frame and back up to a loop in the same spot on the other side.




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[RJ Howell]

[
This lift-top looks like a 50/50 lift. Most are 75/25 or less. That makes them work well. With this, we're far beyond that and what can we recommend as a solution?

What do you mean by a 50/50 or 75/25 lift?

50/50 is what you seem to have 1/2 as the base and 1/2 as the lifted. My future build is a 75/25 lift, 75% is base and 25% is lifted.

When I saw you assisting the lift, I assumed underpowered. You're saying it's air leaks, aye. My thought went to regulators at each lift, meaning they would not activate until certain pressure is built up. Without a controller of sorts, the same amount/length of tubing to each would do the same thing. So even if you were underpowered, they would stop until pressure is built back up and continue. With your current system, this would not be hard to do.

[RJ Howell]

So, with the lifting... we had loads of problems with that. Abs and pvc pipe is very uneven on the inside and my seals would seal for 3 inches of travel, leak for 2 inches, be too tight for an inch, then slide nice and seal, then leak too much to lift....

Personally, I'd can the hard piping and go flexible.

It also doesnt lift evenly because of the rear overhang. The rear cylinders have to lift more than the front and they are the same size

Here's where regulators would assist you. You can dial them in to lift the different weight equally.

Here's where a good ME could help out. I do believe you can achieve the same effect with the amount/length of tubing to each. How much tubing is a math calculation I'm sorry is beyond me.. If you decide to go this way, I do know two that love my questions.. LOL and always help me out. I would reach out if so.

[Pmullen503]

Leaking air cylinders is going to be a problem no matter what. If the leaks aren't too bad maybe a sizable air tank would continue to maintain pressure when one cylinder is leaking. You'd have to pump up the tank first then open a valve to the cylinders. A regulator could limit the pressure.

[John61CT]

I reckon forget hydraulics/pneumatics.

Wire rope pulleys run to common junction point, then pulled by a single winch.

Even hand-cranked if under a couple hundred pounds.

[Postal_Dave]

I'm been following the posts and I just re-watched the video showing the cracks.
OK, I saw the small cracks in the corners of the top part of the camper. There are no pneumatic lifts on the tail corners but there are cracks. There are pneumatic lifts 18-24 inches forward of the tail corners but there are no cracks there. (Or at least I didn't see him showing cracks over the wood blocks that the tail pneumatic cylinders push into) So I'm going to say that I doubt that the lifting mechanism is doing the damage.

(I'm going WAY out on a limb with this guess. I have no expertise in aerodynamics so this is just a guess)

I'm thinking that most of the damage is being caused by the overhang at the back of the camper. Air going past the vertical supports of the overhang is making them flap in the breeze, causing the cracks in the tail corners.
Also, the overhang in the back may be making a low air pressure area and causing it to pull on the foam in the form of drag. That hollow open area has air whipping by it at 60+mph and little air can get into that area, so you could be getting a vacuum effect. The pull of the drag might be the cause of those big cracks in the middle of the top's wall.

My suggestion is build a new top without the overhang.

[GPW]

Pop up is Not an easy thing to do eh ? … I was thinking about a rounded top ( half cylinder ) , where the stresses would be distributed evenly …

[John61CT]

duckworks
http://m.tnttt.com/viewtopic.php?f=5&t= ... 5#p1210338

[Pmullen503]

If the top could be beefed up to handle it, a single pneumatic piston at the point where the top balances might work. That would reduce the problem of each corner lifting unevenly. The piston would have to be double the diameter of the corner pistons. But I'll bet that compressor would lift it slowly enough that you could help any corner that stuck. Once the top is up, you could brace the corners and lower and remove the cylinder.