Is Monday-morning engineering a thing? Care to evaluate my camper lift?

[Jack Olsen]

I recently put together a way to lift up a camper above my driveway so I could park a car underneath it. It's been working without a hitch for awhile now, and I believe it's safe and stable. But I know I'm not any kind of genius -- much less an engineer. So assuming anyone out there's got the time or inclination, I thought I'd invite some constructive pointers and/or criticism from the many guys out there who know more than I do.

I'll try to describe here what I've done. The basic structure of this lift is four pillars, 1/8"-thick 2x4 rectangular tubing, sitting on concrete. There is a rectangle at the top made out of steel, on top of the pillars but also big enough for the camper to move up and through the shape vertically. Two sides of the structure are attached to my house's exterior walls (wood frame, stucco, 10" thick) at multiple points with 12"-14" carriage bolts. The one long side that isn't bolted to the house has a large X-shaped brace to make sure those pillars remain parallel. That side is also bolted to the concrete and tied into the other side with the steel rectangle up top. Because the structure is basically one with the house itself on two perpendicular sides, it appears to have very good rigidity, both torsionally and laterally. (Forgive/correct me if I'm using these terms incorrectly.)

So I believe the basic frame of the thing is strong enough for the task of holding up the camper -- which weighs 1,100 pounds. But the important function of the thing is raising and lowering the camper, which means an 1,100-pound object is put in danger of falling if my system of sheaves, cables and Chinese-made hoist were to suddenly somehow fail. My design for the lifting mechanism is based on what I've seen used in boat lifts. I'll include a crudely-made illustration, which shows how two cradle pieces are raised and lowered by a set of cables and sheaves that generate 8' of lift by moving the hoist-end of the cable a distance of 32'.



The cradles themselves each have a second cable that makes sure they stay level as the lifting force is applied on only one end of each cradle. This cable is anchored at both ends, with one end adjustable so I can make certain the cradle stays level, even if the cable stretches.



And here's the whole crazy idea put to use. It's important to note that nothing is resting on the cables when the camper's been raised up. It's sitting on four 1/2" pins running from both sides of the cradle pieces and through the pillars. (Since this picture was taken, I welded on a rear-end spare tire mount, which will keep the whole thing from sliding forward, and off, the cradle.)



The cable is rated for more than the weight of the camper. Each of the eight sheaves I use is rated for 3000 pounds. The three snatch blocks I use are rated for 2000 pounds. I assume the load of the camper is getting distributed between the sheaves. But you know what they say about assumptions. I try to get my head around where the force is going in this contraption and I don't get very far. But I haven't found any deflection in the axles I put the sheaves on and it seems as though the hoist (rated for 2,000 pounds) isn't breaking a sweat.



The red zone, danger-wise, is whenever the load is moving up or down. Once it's up, it sits on half-inch pins running through each pillar. Once it's down, it's sitting on its own wheels. I came up with a possibly-good-possibly-bad junkyard safety system, which is an inertial-reel seatbelt on each of the four pillars. The idea is that if a cable breaks and the load drops, the seatbelt reels will lock up and stop its descent. I'll admit that I would love to do more testing with this 'system,' and I'll also assure everyone that I would never put anyone or anything under the camper while it's moving. So the worst-case scenario from a drop is a damaged camper.

In an earthquake, the camper would have to jump quite a bit to migrate off of its cradle. It can't simply slide off because of the presence of a wall at one end and the spare tire mount blocking fore-aft movement at the other end. I've also been using a large c-clamp on the spare-tire end to prevent any jumping around if the ground did start moving. (And for what it's worth, in a major earthquake, the least of my concerns would be a damaged camper.)

I'm open to anyone's thoughts on where I might have messed up and I'd be happy to hear any suggestions on how to improve the thing. And of course it might be that you don't feel it needs improving. (My mechanical-engineer father approved of it.) If I disagree with a comment or suggestion, I promise to remain civil. And of course I'll answer any questions I can, since it might not be at all clear how the thing works from my photo and two illustrations.

Your thoughts, Off Topic brain trust?

Oh, and there is a video, where you can see it in action.

Don't judge me by my acting skill:



https://youtu.be/kr5ErGiyylM

[wdfifteen]

Pretty ingenious. I like the seatbelt idea. Very creative.

[island911]

Originally Posted by Jack Olsen

I.. and I believe it's safe and stable. But I know I'm not any kind of genius -- much less an engineer. So assuming anyone out there's got the time or inclination, I thought I'd invite some constructive pointers and/or criticism from the many guys out there who know more than I do.

...

Yeah, THAT's why you posted.

And made a highly edited vid

Oh JO...

[island911]

For criticism, I say the first thing to strike me was, what do the neighbors think of having to look at that trailer hovering just over the fence?

[Zeke]

I thought you'd be a better welder by now. But you sure think 'out of the box'. From what I see there will be no problems with the function of that lift. Might even be some secondary uses there.

Wow, time flies, Molly proves that given the last time I saw a pic she was, let's say, a toddler.

[gduke2010]

Being approved by an engineer is a good piece of mind. The one thing that would concerne me is the seatbelt mechanism, wonder what you could upgrade, too?

[look 171]

I am with Island. Your neighbors, will they call the city on ya. You are out on the west side, so they get pretty nasty out there? If they see that, it may last three to five days tops. News spread like wild fire especially with that Nextdoor BS. Someone wouldn't like that

I have to say, that's a pretty cool idea.

[Scott Douglas]

The only thing I don't like about it is the tear out distance on the bolt I circled in the picture.
(This is coming from a non-engineer, but someone who spent a good deal of time working with some really smart people who were making things to build satellites and the tools to lift them a lot higher than 8 ft.)

[island911]

I'm guessing that you got the cable level idea from one of those old school drafting tables.

[stomachmonkey]

You have entirely too much free time on your hands.

Thats not a dig, it's envy.

Nice work.

[Bill Douglas]

Before I read the other comments; my first thoughts also were the neighbors (not the TV show). I had site office, we call them a portacom, next to the boundary fence and some moron woman complained it may blow over in a storm... Meetings and 20 emails later I lost the fight with the city over it and moved it. So I recommend turn up at the neighbors with a whole lot of alcohol or cash and explain how sorry you are etc before it hits the fan.

[john70t]

I thought there was a similar thread from some guy living in Tokyo.
It is an awesome idea. I've got a one-lane drive with limited room as well.

Not an engineer but here are some ideas:

(please don't get too impressed with the artwork)

[oldE]

Jack,

I could see the longitudinal bracing on the uprights next to the fence, but what keeps the framework from collapsing away from the building? Is it tied into the building? Is there something more solid than a fence on the opposite side?

Actually, I loved this thread from the moment I read, " I recently put together a way to lift up a camper above my driveway so I could park a car underneath it. It's been working without a hitch for awhile now," Put a hitch on that sucker and go camping!

Best
Les

[javadog]

Got an adequate load rating on the eyebolts? They are probably fine, but they are normally intended for loads in a different direction.

[wdfifteen]

^^
Those look like forged eye bolts with a boss that is pulled up tight against the steel frame. If they were hanging out the shank would see a bending stress and it could overload the top side of the shank, maybe to failure. But with these forged eye bolts installed this way the shank of the bolt is in shear - a much stronger position for them.

[javadog]

Most eye bolts that are rated for lifting are intended for use when the load is limited to 45° or less off axis. I've never seen a rating for one at 90°.

They make hoist rings for lifting it angles greater than 45°, but they seldom are rated for anything approaching 90°.

Not saying it's going to fail, but I wonder if that was a consideration.

[wdfifteen]

They are rated for loads less than 45 degrees.

[vash]

oh o..off to a bad start.

it was Friday yesterday..not monday

[hcoles]

Originally Posted by Scott Douglas

The only thing I don't like about it is the tear out distance on the bolt I circled in the picture.
(This is coming from a non-engineer, but someone who spent a good deal of time working with some really smart people who were making things to build satellites and the tools to lift them a lot higher than 8 ft.)

Good point - I would move the eye bolt to the top rail so the "rope" pulls close to inline.
Comment - I'm not sure I like rope for this. Running rig cable is probably better but more expensive and requires crimping. Also you are not using thimbles and IMO should.

[hcoles]

Oh I see better now - you are using cable.