One for the Engineers & Inventors

Submitted: Wednesday, Apr 08, 2009 at 15:03
ThreadID: 67681 Views:7818 Replies:7 FollowUps:11
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Hello All

I am about to commence on this years project, a tandem off road pop top camper trailer.

I have purchased many of the components for this project including a tandem 2.5 tonne Simplicity Suspension.

The main body is 4.2 metres long which includes a rear section that folds down and incorporates a shower/toilet and entry to inside.
I have researched many options from hydraulic cylinders, 12v electric telescopic actuators, gear driven worm drives and every option comes close to approximately $4,000.00 for components.

Although the camper is expected to cost about $35K for components and materials, I cannot convince myself that it should cost $4K to lift the roof.

The roof complete with insulation, lining, retractable Air Conditioner and a 80kg tinnie will be approximately 225 kgs so I am using a figure of 350kgs as the total weight.

I do not want to use the Jayco / Coramal wire and winch system as they are susceptable to failure and will not handle this weight.

If anyone has any suggestions on a reletively simple and cost effective method to raise the roof 900 mm's I would appreciate your advice and input.

Yes I have considered parking under a tree and using a chain block, fitting a HIAB crane to the drawer bar and getting the "Men from Mars" to follow me around with a crane. All of these ideas were scrapped when I pulled the last strand of hair from my head.

Your help would be appreciated.

Regards and Happy Easter to All.

John
Life isn't about how to survive the storm, but how to dance in the rain!

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Reply By: austastar - Wednesday, Apr 08, 2009 at 15:11

Wednesday, Apr 08, 2009 at 15:11
Have you considered airbags and compressed air?
There are companies who make life rafts etc that may be able to fabricate some thing that will work.
AnswerID: 358799

Reply By: GoneTroppo Member (FNQ) - Wednesday, Apr 08, 2009 at 15:42

Wednesday, Apr 08, 2009 at 15:42
A slightly larger/longer version of a old fashion scissor car jack on each side.
You could power this plus have the fallback of manual windup just in case
AnswerID: 358807

Follow Up By: Member - John M (NSW) - Thursday, Apr 09, 2009 at 07:11

Thursday, Apr 09, 2009 at 07:11
Hi Troppo

This is the system that I am seriously considering using and has all the mechanical and simple advantages.
I will still need to use telescopic sections on each corner to achieve lateral support for high winds with the weight. As I want to leave the tinnie on when travelling and just doing overnight stops. My biggest problem with this system is to make it compact and conceal the long threaded bars and 2 gearboxes on the front corners and also a middle gearbox for the motor or winding mechanism.
I saw a truck similar to your picture towing a pop top caravan on the M2 in Sydney last Sunday. If that was you it was a good looking jig.
Regards John
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Follow Up By: GoneTroppo Member (FNQ) - Thursday, Apr 09, 2009 at 07:44

Thursday, Apr 09, 2009 at 07:44
John, Glad you like the idea, I try to keep KISS in mind always.

To avoid having to have corner telescopic sections, it may be possible to use another two scissors front and back but without the threaded bar ie support only, no lift. Or maybe a horizontal spring to assist lift.
I seem to remember early factory built VW campers used such a system

Industrial scissor lift platforms, seem to achieve terrific lateral stability just from the mechanical action of the scissor.

Alas it was not I in Sydney, I've been chained to a desk working, (well mostly anyway) Like most my camper is a work in progress but I've almost got it perfect!!
Liked the sound of your project though, this way you should finish up with exactly what you want.
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Reply By: Nomadic Navara - Wednesday, Apr 08, 2009 at 15:52

Wednesday, Apr 08, 2009 at 15:52
I see nothing wrong with the Coromal/Jayco systems in principle, the problem is they are engineered to lift a lot less weight than you will have. Try a ships chandler for heavier components and cable and you should be able to construct something more robust.

PeterD
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Reply By: ob - Wednesday, Apr 08, 2009 at 16:47

Wednesday, Apr 08, 2009 at 16:47
If you can find (in your state obviously) a company that sells those chinese brand engine lifting cranes, the type used in garages usually on small wheels, I think they come with a long stroke hydraulic cylinder and pump all in one.I know there is a couple here in Perth that do. I think you can get the whole shooting match for about $300-$400. I'm also pretty sure you can buy the complete cylinders as a separate part and if my memory serves me any way near correctly they ranged up to about 5 tons capacity.


Cheers ob
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Follow Up By: Member - John M (NSW) - Thursday, Apr 09, 2009 at 07:15

Thursday, Apr 09, 2009 at 07:15
Thanks Ob

I have looked at these and the problem I have due to the length of the cylinder and stroke required is to gain access to servicing the cylinders after assembly in the event of a seal leaking. The cylinders need to be housed inside the telescopic rams to provide lateral support and take any side loading off the rams which would bend the shafts.

Regards John
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Reply By: Member - Kiwi Kia - Wednesday, Apr 08, 2009 at 17:00

Wednesday, Apr 08, 2009 at 17:00
Have a chat to Willem, he is pretty good at designing & knocking up handy bits out of MDF :-))

I like the air ram idea but only to raise the roof. Then fold up (or down) some supports that will hold everything up if the air leaks down. (I would not use mdff)

.
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Follow Up By: Member - John M (NSW) - Thursday, Apr 09, 2009 at 07:01

Thursday, Apr 09, 2009 at 07:01
Hi Kiwi

I will try and stay away from the MDF but I do notice Willem is pretty handy with this stuff.
I have looked at pneumatics but the problem with pneumatics is these systems normally operate quiet fast and I still have to put cylinders inside telescopic supports to achieve lateral support in high winds.

Regards John
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Follow Up By: Member - Kiwi Kia - Thursday, Apr 09, 2009 at 07:43

Thursday, Apr 09, 2009 at 07:43
Hi again John, Agree with your comment about the lateral supports but I was meaning that you need only use the air for initial lifting and then use another "system" to hold everything in place. The speed of an air ram can be throttled back using restrictor valves but this could be problematic as you do not want one corner flying up ahead of the others !

.
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Reply By: Member - Scoof (SA) - Wednesday, Apr 08, 2009 at 19:38

Wednesday, Apr 08, 2009 at 19:38
Hi John ,

I was wondering if you have ever come across the Prattline caravan system. I think it was a hydraulic a ram in each corner and a hand or electric pump on the draw bar.
But I suppose 4k is would be what it would cost anyway.

It's only money. LOL

Cheers Scoof . :-)
AnswerID: 358853

Follow Up By: Member - John M (NSW) - Thursday, Apr 09, 2009 at 07:22

Thursday, Apr 09, 2009 at 07:22
Hi Scoof

I think I just have to convince myself that it's only money and spend it where it's required.
Lifting and lowering the roof is a major function of the camper and if it does not work properly and be reliable I will have continual problems.
I am building this camper to be indestructable as possible and spending the money in the right area is important. I thought someone here might have some great idea that I have not investigated.

Regards John
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Follow Up By: Member - Scoof (SA) - Tuesday, Apr 14, 2009 at 15:50

Tuesday, Apr 14, 2009 at 15:50
John I was talking around the camp fire about this thread and a guy there had made his own 4 rams and said he didn't have any problems at all .
He made the outer part of the ram from 32mm copper tube and the inside from Stainless Steel tube. He had a guy make a bosses for bottom of each ram to take 3 orings and a boss for the top of the ram with a lip seal he copied the the prattline system for his camper.
He said it was so easy he would do it all again.

Cheers Scoof. :-)
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Follow Up By: Member - John M (NSW) - Wednesday, Apr 15, 2009 at 07:03

Wednesday, Apr 15, 2009 at 07:03
Hi Scoof
I didn't think by problem would be that interesting or important to come up at a camp fire conversation but it is great to get the support and ideas from other members.
The hydraulic system is certainly proving to be the most cost effective method for lifting.
I would be happy to get some ideas from your friend. I have just found a supplier who can manufacture 4 x 1200mm stroke rams for me at about $380.00 each plus the cost of a hand pump and tank, manifold block and some pipework, I think I will get away with this system for about $2k.
This system is fool proof and parts are easily available and I have developed a design where I can remove the hydraulic rams for servicing from the underside of the chassis except that I will have to lift it up to have enough height to remove the rams. Hopefully this will never happen but one has to prepare for the worst.
Thanks for your thought and advice.
Kind regards
John
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Reply By: Louie the fly (SA) - Wednesday, Apr 08, 2009 at 20:11

Wednesday, Apr 08, 2009 at 20:11
John, what about these ideas?

A rack and pinion. You can buy rack by the metre, and then build a winder mechanism - that could work simply.

or

You could make your own linear actuators by using some threaded bar. 25mm high tensile threaded shafts with a brass nut which is held captive in a housing, and spins around via a worm gear drive. Like a Hywema truck hoist.

or

You could use some pulleys and a 12 volt boat winch. Put slides on each corner, like fridge slides.

The linear actuators may work but to lift 900mm you're looking at a hefty priced unit, and you need 4. And I'm not sure if they can support the weight. We use them in a horizontal position generally, or vertical in light duty applications. Have you ever seen those jacks they use to put transportable houses on & off low loaders? An air cylinder with a 900mm stroke will also set you back a bit. Any way you go, an automated system will be costly IMO.

Good luck with it.

Louie
AnswerID: 358857

Follow Up By: Louie the fly (SA) - Wednesday, Apr 08, 2009 at 20:17

Wednesday, Apr 08, 2009 at 20:17
I just read Gonetroppo's post again and it gave me an idea. A scissor action lifter that winds up & down by way of 2 synchronized drives that wind around a quadrant. It would work along the lines of a car window winder mechanism and would have considerable load lifting capacity if designed correctly. Drives would need to have a reasonable amount of torque and be compact. I know someone that could design it (hint hint).

Louie
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Follow Up By: Member - John M (NSW) - Thursday, Apr 09, 2009 at 07:35

Thursday, Apr 09, 2009 at 07:35
Hi Louie

Your option 2 along with the scissor lift is the most simple and fool proof method that I have come up with and I can build it both with a motorised lift and have mechanical backup. No hydraulic oil to leak, no electrics to fail except the drive motor and no cables to break and it will always stay syncronised.

I also like the idea of a quadrant except the it may be very larhe and housing it could be a problem. Any ideas are welcomed.

I really like the linear actuators and can get them with the stroke and lift capacity that I need from Motion Control Industries, what worries me is the electronics and electrics for the syncronisation. More to go wrong and fail and in the middle of the bush if I can't raise the roof or lower it may not be a good look with the bride.

Thanks for your good advice.
Regards John
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Follow Up By: ross - Thursday, Apr 09, 2009 at 09:59

Thursday, Apr 09, 2009 at 09:59
How about something like an exhaust jack placed under the centre of the roof to get it to height so you can push some pins in to hold the load there.
If the jack was placed on something like a sturdy tool box 4-500mm off the ground then the distance would be halved.
The box could be used for storage and placed outside once the roof was up
Having the roof keenly balanced would be important
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