Monday-morning-quarterback my design work?

[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 guys 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 or concrete footings. There is a rectangle made out of steel at the top of the pillars, big enough for the camper to move up through the shape vertically. Two sides of the structure are attached to my house's walls at multiple points with 14" carriage bolts. The one long wall that isn't bolted to the house has a large X-shaped brace to make sure the pillars on that side remain parallel. It's also bolted to the concrete and tied into the other side with the steel rectangle up top. Because the structure is tied into the house itself on two perpendicular sides, it seems 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 a Chinese-made hoist were to suddenly fail. My design for the lifting mechanism is based on what I saw 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 is always level.

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.

The 1/4" 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 ****** 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 easy 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. (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 doubly 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 approves 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, Garage Journal brain trust?

 

[matt_i]

It looks like its working well

My only concern is in the cable itself, I can't see your details from the pic, cables moving over sheaves stresses it, larger sheaves are always preferred when possible. Also there's a super-flex cable that's built with finer wiring so to speak. There is wire rope lubricant which helps the cable to flex over the sheaves.

I don't know if you went with copper sleeves "nicopress" or used U-bolts, but its OK to double those up. Thimbles should be used where loops are made over bolts or pins to avoid wear on the wiring.

I like the X-bracing front to back but do you have an equivalent anti-racking detail for side-to-side?

Great idea and seems nicely executed!

 

[dfiler2]

Great idea and use of space, it looks well built and well thought out. Congrats on adding a new parking space!

 

[Jeepster04]

After quickly looking at the setup, when a pulley redirects the cable 180 degrees, the pulley is seeing the tension in the cable x2. Keep that in mind when anchoring the pulleys and using a pulley rated at a certain load...

It makes sense if you draw a free body diagram...

If the cable has 1,000lbs on it, for example, the pulley will see 2,000lbs.. Again, maybe you mentioned that, I just quickly glanced over everything..

 

[maxpat82]

very well thought.

I'm no engineer, but I don'T nothing worrying me. everything seems well overbuilt with a good safety margin (look like x3 everywhere)

I doubt the safety betl would do anything in case of a locking pin break.

ps.: when sitting on the pin(as well as went moving up and down) if the weight of the camper is pretty much centered on the lifting arm: all the weight is egally distributed to each lift point (So let exagerate at 1600lbs for the camper and lifting arm toatl weight: that would make only 400lbs of load to each cable end and lock pin.

 

[Trey T]

It looks good and structurally sound...

 

[shepherd]

Only thing I`d add is if you ever get a brake line leak in the camper, say goodbye to the paint on the Benz....

Mores seriously, you must have some pretty cool neighbors. I could see certain types chirping about it...but then again, I live in a town where you have to get a permit to build any shed larger than refrigerator.

 

[ducksface]

Due to creep, and I don't know how my stuff moves on its own, but it does:
I'd add some sort of restrictive bracket to the rear bumper of that trailer. Just a piece of angle, some pins, something, to the front edge and rear edge so the trailer bumper can't slide off from wind creep or an accidental bump to that lift rack.

Right now as it is, I can see a wayward wind or a missed brake pedal when backing in the
car under, bringing that trailer forward enough to jog itself off of that bumper.

 

[LXCam]

I'd X brace the left side like the right. And I'd build four bolt on diagonals to go between the stanchions and the support frame even if they were only a foot to 18" long.

 

[Falcon67]

I just have two comments -
1) You people live too close together LOL
2) if you are using one of the less expensive import electric winches, I'd make sure you're using one with at least double the rating of your dead weight. Yes, the sheaves, etc reduce the load quite a bit. The larger models "seem" to do better. I use a HF 2500 to winch our 1450 lb dragster into the trailer. That's a pretty light rolling load that we can do easily by hand just by using the 32" rear tires. After several months of use, the winch has become way less reliable when pulling under load. The brake hold fine, but extension and retraction have become very "jerky" - not good for a suspended load. Of course this is a $49.95 coupon special and not a $200+ SuperWinch.

 

[maxpat82]

I'd X brace the left side like the right. And I'd build four bolt on diagonals to go between the stanchions and the support frame even if they were only a foot to 18" long.

it's bolted to the house...I think the house structure is enough of an X Brace

 

[LXCam]

it's bolted to the house...I think the house structure is enough of an X Brace

I can't tell if that's the house or just a block wall. Regardless I'd still do what I suggested and after relooking at the pic would do a diagonal on the top frame at all four corners. I've spent my entire adult life building in Ca and I've seen first hand the way structures can move and separate depending on the type of quake. Jack asked for $.02, I gave my $.01.

 

[RVDan]

My primitive math says everything has more capacity than you need.

An engineer will tell you the individual parts have more capacity than you need but as a whole you're going to kill yourself and everyone around you.

 

[Jack Olsen]

Thanks, guys. I expected this to go much worse.

It looks like its working well

My only concern is in the cable itself, I can't see your details from the pic, cables moving over sheaves stresses it, larger sheaves are always preferred when possible. Also there's a super-flex cable that's built with finer wiring so to speak. There is wire rope lubricant which helps the cable to flex over the sheaves.

I don't know if you went with copper sleeves "nicopress" or used U-bolts, but its OK to double those up. Thimbles should be used where loops are made over bolts or pins to avoid wear on the wiring.

I like the X-bracing front to back but do you have an equivalent anti-racking detail for side-to-side?

Great idea and seems nicely executed!

Thanks. The cable is 7x19 galvanized. The sleeves are aluminum, and most are doubled. I have cable stops for the ends, but haven't put them on yet. I planned on X bracing the other side and also adding something up high for the short sides, but it's just so unshakeable the way it is now that I've held off. The walls wood-frame, clad both sides in stucco, and 10" thick.

There is a 14"-thick solid wood beam on the un-exed side that I notched and drilled through.

After quickly looking at the setup, when a pulley redirects the cable 180 degrees, the pulley is seeing the tension in the cable x2. Keep that in mind when anchoring the pulleys and using a pulley rated at a certain load...

It makes sense if you draw a free body diagram...

If the cable has 1,000lbs on it, for example, the pulley will see 2,000lbs.. Again, maybe you mentioned that, I just quickly glanced over everything..

That was one of the things I learned in working this out. But I'm also thinking (maybe correctly, maybe not) that the load is getting distributed somewhat among the 11 pulleys involved.

very well thought.

I'm no engineer, but I don'T nothing worrying me. everything seems well overbuilt with a good safety margin (look like x3 everywhere)

I doubt the safety betl would do anything in case of a locking pin break.

ps.: when sitting on the pin(as well as went moving up and down) if the weight of the camper is pretty much centered on the lifting arm: all the weight is egally distributed to each lift point (So let exagerate at 1600lbs for the camper and lifting arm toatl weight: that would make only 400lbs of load to each cable end and lock pin.

The pins are in a multiple-shear configuration, which is my way of saying they go through a piece of steel, then two sides of the rectangular tubing, then another piece of steel.

Only thing I`d add is if you ever get a brake line leak in the camper, say goodbye to the paint on the Benz....

Mores seriously, you must have some pretty cool neighbors. I could see certain types chirping about it...but then again, I live in a town where you have to get a permit to build any shed larger than refrigerator.

No brakes on this camper. But sometimes I get condensation/dew that drips down.

There's a kind of facade where the gate opens -- it's actually a walled roof section that covers about 8' of the driveway. It blocks the view of the camper from the street. And it's not visible from any of the neighbor's windows.

But yes, I'm lucky to have the neighbors I have -- and the lack of a HOA.

Here's the view from the street.

Here's the view from above.

Due to creep, and I don't know how my stuff moves on its own, but it does:
I'd add some sort of restrictive bracket to the rear bumper of that trailer. Just a piece of angle, some pins, something, to the front edge and rear edge so the trailer bumper can't slide off from wind creep or an accidental bump to that lift rack.

Right now as it is, I can see a wayward wind or a missed brake pedal when backing in the
car under, bringing that trailer forward enough to jog itself off of that bumper.

That's a good point. I initially had a bolt going through the bumper with a steel stop that would swing down from it. But then I welded on the spare tire carrier, which drops down and provides the stop you're talking about. (I realize now that I don't have a picture, though.)

I'd X brace the left side like the right. And I'd build four bolt on diagonals to go between the stanchions and the support frame even if they were only a foot to 18" long.

That was my original plan. But it is just so stout, right now. The walls are wood-frame exterior walls. I try shaking the structure from the exposed legs when the camper is in place and it's amazing how sturdy it feels. But your point is well made, and appreciated. I'm going to think about it.

I just have two comments -
1) You people live too close together LOL
2) if you are using one of the less expensive import electric winches, I'd make sure you're using one with at least double the rating of your dead weight. Yes, the sheaves, etc reduce the load quite a bit. The larger models "seem" to do better. I use a HF 2500 to winch our 1450 lb dragster into the trailer. That's a pretty light rolling load that we can do easily by hand just by using the 32" rear tires. After several months of use, the winch has become way less reliable when pulling under load. The brake hold fine, but extension and retraction have become very "jerky" - not good for a suspended load. Of course this is a $49.95 coupon special and not a $200+ SuperWinch.

I have the 'big dog' of the HF hoist line. I say that with some irony. It's a hoist, not a winch, for what it's worth. And it always bugs me how hoists get set up so their pulling away from their mounts when they're under load. So I did something odd. I cut a hole in the frame of the hoist itself:

And then I mounted it so the force of the load pushes it back against the wall it's attached to. The wire road goes through a cutaway in the wall itself.

It's also sheltered from the weather this way. I'm going to run a permanent power line to it, with a switch that requires a key for the power to go on.

My primitive math says everything has more capacity than you need.

An engineer will tell you the individual parts have more capacity than you need but as a whole you're going to kill yourself and everyone around you.

The engineer is probably right.

But until then, I'm going to enjoy my open driveway.

And wait, what would it be without the promotional video. I recorded it all in about 20 minutes, and then learned that the mic was turned off. So my daughter and I had to dub our own dialogue. She's pretty good; I'm, uh, not.

 

[MikeF2316]

What I notice - and keep in mind I'm no expert in this sort of thing - is that your sheaves may be a little small, so the cables may not last long. But this wouldn't cause them to fail suddenly, but keep an eye out for fraying.

And I hope you took snow load into account.

 

[Jack Olsen]

I got my pulley sizes from existing 5000# boat lifts. But the pulley size on the ****** block in the picture is only 3". Here's why.

Initially, I had a bad idea. I thought I would have a single cable for each cradle. So in addition to all the stuff for lifting the two sides at the same time, the same cable would go under the pulleys on either side of each cradle, like this:

There were two downsides to this idea. One was that for it to work, the wire rope and pulleys had to change direction/orientation. A cable would come across the length of the cradle piece and then turn 90° for the movement that runs parallel to the main long-way beam on its way to the hoist. I don't know if this is an engineering no-no, honestly. But it kept bugging me -- it seemed like a good way to get the cable to jump off of a pulley.

The other problem was that there was nothing in this two-pulley-per-cradle configuration that would force the cradle to remain level. My thinking was that the load would be substantial enough that the two pulleys would each do 50% of the work. But when I tested it with no load, the tendency of one pulley to start moving before the other produced consistently uneven lifts. I couldn't think of anything that would guarantee that the load would stay level (for example, was the trailer's weight really split 50/50 L/R?) So I stopped for a few hours and re-thought how I was going to do this.

The upshot was that I cut each cradle and flipped one side and used the leveling cable that was anchored on both sides and not connected to the lift mechanism. I know that it works now, since it always does. But when my brain tries to get around why the static/leveling cable works, I draw a blank. It's flippin' voodoo, to me. But it works.

But here was the problem. That original scheme also produced one layer of reduction (I'm sure that's not an engineering term), meaning the load was cut in half, but the distance of necessary cable travel was doubled. But when I got rid of the original scheme and put in the static/leveling cable, I was back to 1:1. So I added a ****** block on each cradle and had a U-shaped cable lift each cradle, anchored at one end and pulling at the other. It returned me to 16' of cable travel for 8' of cradle/camper travel. (And I had one more layer of reduction upstream of that, for 32' of total travel to lift the camper 8'.)

Does any of that make sense? It might not; I'm not used to writing about this stuff. But I had one 2000# ****** block on hand, which I used for testing. And since the test worked, and the capacity of the ****** block seemed adequate, I just ordered some more of the same ****** block -- which used a 3" pulley. So my three ****** blocks use smaller pulleys than the regular 4" ones, which are rated for 3000#.

 

[southalabama]

You could always borrow Elon Musk's boring machine for a weekend.

Looks good. For a non designer you are a pretty good designer. From cake pan lights to repurposed cabinets and now a lift system.

 

[tab2]

How about the title? Isn’t the thread title a statement and not a question so it should not end with a “?”?



Aren’t you a writer?

 

[rsanter]

Well as an engineer I am impressed, you made your own vehicle lift basically.
Overall you have a good design with limited deficiencies , and the deficiencies should not really hurt you for the way you are using this thing IMO.

There are a couple of things that do concern me a little.
The cables, be sure you keep up on them and maintain them in good shape. Basically regular inspection.
The cable crimps. I know they are strong but they always concern me. Be completely sure they are up to par as that is a single fail point that can make,for a bad day. Inspect them as over time corrosion can have bad effect.

Your pullies. I would be most concerned with keep them lubed and clean.

The eyelet you are attaching the cable ends to. You have them oriented in a bending moment. They are strongest in pure tension. Be sure the specification for them is proper for the orientation of the force applied to them. They may be fine but check their specs

Other than that looks good,to me

 

[helterskelter]

I am an engineer. The welds honestly look like they could have used more heat. Probably strong enough, but I would keep an eye on them and check regularly for crack indications. Not trying to criticize just providing feedback requested.

As for the actual design it looks fine from here and structurally sound.

My only other comment would be in the event it did fail. Would your insurance be OK with parking a camper on a homemade structure above the car? Everything is a risk/reward type of balance.

 

[NUTTSGT]

Jack, first things first. Cute daughter, she has a future in show business.


Secondly, what are the eye bolts (cable anchors) rated for ?

 

[Firebrick43]

Actual engineers saying its looks ok??

Lifting equipment is ALWAYS is bjilt to a 5:1 safety factor on the cables. Why, loads can go through the roof when things jamb, cables jump their sheath, or crevice corrosion takes its toll on the nicopress.

I dont have an engeering degree, just a maintenance repairman in the factory with the most bridge cranes in the world, some are 80 tons. And even with such safety factors i have seen 3 cables broken personally in my 14 years. Dont take my word for it tthough. I developeed a good relationship with my machinery handbook and would suggest you do the same.

 

[helterskelter]

Actual engineers saying its looks ok??

Home built trailer lifts aren't held to the same standard as lifting equipment in a factory.

 

[1redTA]

I like it, if you have a good feel for it after watching it operate cool, don’t trust anything always verify the pins are holding everything in the up position

 

[Firebrick43]

Home built trailer lifts aren't held to the same standard as lifting equipment in a factory.

Why should they not be? Is your life, wifes/kids, or friends or neighbors worth less just because its not in a commercial or industrial setting?

That kind of thinking made my second cousin a vegtable when the cable he was using to pull out a semi snapped and caught him across the forehead. For 8 years, when he finally sucumbed from pneumonia, the only interactions with the world was a smile when you placed a sucker on his tongue. Very hard on his mother to outlive him. Luckily he didnt orphan or widow anyone.