Lifting Mechanism?

[starleen2]

Ok, so here goes at an attempt at a lifting mechanism. This mechanism is for the Lady Bug hatch which weighs about sixty to seventy pounds. I don’t want to use gas spring due to the fulcrum force exerted on the hinge when trying to close the hatch. Linear actuators are out of the question due to cost. I did some research on the pop up camper mechanism. It seems that many use either a cable or spring type lifting mechanism. I’m going with springs (Goshen Lifting type). The spring is similar to a sewer snake (the beefier type). The advantage of the spring type is that the spring is flexible and when in compression – it’s almost like a flexible steel rod – but it has to be encased in a tube or else it’ll bend when in compression and we don’t want that do we? The spring is then inserted into a guide tube and pushed along inside the tube. The other end of the spring is inside another smaller tube that is pushed outward. I need about 17” of travel to lift the hatch completely. I plan to use a 24” scissor jack to do the pushing – Pulling is different, gravity takes care of that. The jack can then be cranked via a crank rod on the side of the camper. All this will be mounted under the camper with the tubes exiting out the wheel wells. Here is a simple illustration: The green is the spring inside the tubes. All right engineers, ready for suggestions.

[kennyrayandersen]

I guess I'm not quite getting it. How about a simple pencil sketch that shows:
1) the hinge line of the hatch
2) attach point of your snake spring
3) how the spring travel make the hatch open.
Maybe I’m not seeing the simple beauty of the spring, but if I remember correctly there is a fair amount of room in the inside – how about an over-centering rod that props it up – It could be driven by a rope(s) or levers from the outside [even].

[bobhenry]

oops dup

[kennyrayandersen]

http://www.hauntedattraction.com/workshops/cylinder.html

AIR RAM ANYONE ?

Might be a slight drawback:

Compressed air source (compressor)

The 12 volt car ones wouldn't be so good as high pressure low volume... Hmmm Foot Pump?

[bobhenry]

http://www.hauntedattraction.com/workshops/cylinder.html

AIR RAM ANYONE ?

http://www.llund.com/pne_cyl.htm

[hugh]

how about using an electric motor from a power window assembly? Maybe with a simple pulley system of some sort.

[Jiminsav]

wouldn't the spring put just as much stress on the hinge?
is there a problem with you lifting the hatch? wouldn't a simple wooden prop hold it open?

[Barefoot]

I agree that to do the job, the sewer spring (whatever) causes the same stress as the gas springs. The key is fastening the top, hatch ends of whatever you use towards the handle end of the hatch sides, to lift the handle part, not to the hinge end, to try to lift the hinge.

[RAYVILLIAN]

How much do the springs cost? I've given some thought to the ball screw from a 1 ton 12 volt scissors jack but than you would still have the problem of the fulcrum force that you mentioned. Your drawing looks like it would work if I'm visualizing the rest of the pic right...the tubes would go up the back wall and springs would raise the hatch at the back....right?

It would be more complicated to install than air rams though.
Gary

[Lou Park]

How far up is the total travel?

[starleen2]

Barefoot
I agree that to do the job, the sewer spring (whatever) causes the same stress as the gas springs. The key is fastening the top, hatch ends of whatever you use towards the handle end of the hatch sides, to lift the handle part, not to the hinge end, to try to lift the hinge.

Not really – Imagine a see saw – when you push down on one end, because of the fulcrum point, the other end moves up – there will always be some force exerted up at the hinge joint even with gas springs – some have literally popped the hinge off the galley with them.Yes they’ll probably work – But I still have to lift the hatch, something I don’t want to do (read below) – would rather crank and let the mechanic do it for me – Now how cool would that be? Back to the conversation, now image a sheet of plywood and pick up one end – all the force is a rotation force at the hinge and the hinge is NOT under any lifting force. This mechanism is almost the same as the pop up mechanism except they are using a cable to drive the springs, and for simplicity, I using a scissor jack.

Here is a link
http://www.customcylindersintinc.com/camper_trailer_roof_lift_system.htm

Jiminsav
wouldn't the spring put just as much stress on the hinge?
is there a problem with you lifting the hatch? wouldn't a simple wooden prop hold it open?

That’s what I’m using now! No problem opening the hatch – Just wanted something to do it for me

RAVVILLIAN
How much do the springs cost? I've given some thought to the ball screw from a 1 ton 12 volt scissors jack but than you would still have the problem of the fulcrum force that you mentioned. Your drawing looks like it would work if I'm visualizing the rest of the pic right...the tubes would go up the back wall and springs would raise the hatch at the back....right?

Bingo – you got it - A 50 ft spring costs about $25.00 and is about ½ inch in diameter – more than enough. I thinking of using thin wall electrical conduit to route the spring in. Lowes has them in stock and harbor freight has the Jack

Lou Park
How far up is the total travel?

Depend where you place it – I need about 17 inches of travel

[cokebottle10]

I'm thinking that if you used a set of pulleys and a small boat winch it would be cheaper and easier to install.

I hope I can explain this well enough that you can visualize it. Think of a bow and arrow pointing toward the sky with the arrow drawn back fully and the tips of the bow are now next to the arrow. Now think of the tips of the bow as two fixed points beside the arrow and forget the bow. Also think of the end of the arrow having a pulley were it touches the string. If one tip holds the string (cable) and the other tip is a pulley, Then you could pull the string (cable) around the pulleys and the arrow (rod) would raise and push the hatch up. The arrow (rod ) would just need a guide at the top. Mounted like this the rod would travel half as much as the cable is pulled.

If you wanted you could get a car electric window motor to turn the winch. You would also need a access point to the cables and winch to maintain them and to disconnect them in case they fail.

PS I love your ladybug trailer. Thanks so much for posting the build.
David.

[starleen2]

I'm thinking that if you used a set of pulleys and a small boat winch it would be cheaper and easier to install.

I hope I can explain this well enough that you can visualize it. Think of a bow and arrow pointing toward the sky with the arrow drawn back fully and the tips of the bow are now next to the arrow. Now think of the tips of the bow as two fixed points beside the arrow and forget the bow. Also think of the end of the arrow having a pulley were it touches the string. If one tip holds the string (cable) and the other tip is a pulley, Then you could pull the string (cable) around the pulleys and the arrow (rod) would raise and push the hatch up. The arrow (rod ) would just need a guide at the top. Mounted like this the rod would travel half as much as the cable is pulled.

If you wanted you could get a car electric window motor to turn the winch. You would also need a access point to the cables and winch to maintain them and to disconnect them in case they fail.

PS I love your ladybug trailer. Thanks so much for posting the build.
David.

That is the way a Coleman lift system works – Others’ on the forum have done similar. Will it will work, yes – however I’d rather not mess with pulleys and cables. With the spring method, I get a smaller diameter tube and I don’t have to mess around with pulleys and cables.
PS> Thanks for the complement

[cokebottle10]

Other than finding a tube to fit closely inside or outside of the EMT I do not see a problem. Maybe a old tent pole? I did not think that you could get the spring that cheaply. You may have a problem with water getting in the tube from rain or condensation.

It looks cleaner than the pulleys and cable. But not as versatile. The pulleys system can be mounted any where. I think that the push spring system needs to keep the springs close to the same length on both sides. It also looks like you can raise the hatch by hand (if needed) if you do not attach the spring driver bar to the jack. I really like that. I also think that the spring driver bar needs to be in some kind of track to keep it straight.

Thanks,
David.

[starleen2]

This is what I'm trying to accomplish, but without the cable pulley and less two front tubes