Lifting vehicles with 4 points of contact

[OWN9494]

Hello all. Just a quick fyi...I have never taken a physics class although I did want to in high school (many years ago). I am just looking for an answer to a very complicated (yet simple looking on the outside) problem I am having. In my job (towing 13 years) I use physics daily even though I don't know all the math behind it. Sorry in advance for my ignorance in this field of study.

I am in the design process for a vehicle lifting apparatus that will be used to pick vehicles up from a lifting point above the vehicle with attachments going to the wheels (strongest lifting point on a vehicle). The UK uses tow truck cranes all the time but I am in the US and we don't tow vehicles that way. We do however have to use whatever means necessary to remove vehicles from unwanted situations. Such as on top of a parking curb or a vehicle that has the under carriage sitting on the edge of a road in the ditch. Up until this point we have always been able to get the job done but we know of a much easier way but don't currently have the equipment for it. This is where you guys come in.

To put simply the frame base for this can be seen at this link.
http://www.caldwellinc.com/strong-bac/spreader-beams/four-point-end-fitting-system

Now that we have a basic understanding of what I am after I can get to the next part. I do not intend on copying this manufacturer's work. There are many different kinds out there but none are specifically for vehicle recovery. Also I do not intend to sell any products to anyone. This is for our personal use.

I intend to use a different corner piece that can have a working load limit(WLL) of 7 tons for each corner. Although I may need more or less depending on what you guys come up with on the next part.

The part I badly need help with is the poles in between. I am not sure if we should use hollow or solid, aluminum or steel, or the thickness required to have a total WLL of at least 10 tons. The tubes will also have to have different lengths for different vehicles. I plan on having 2 or 3 different four piece tube sets because of this. A smart car(1,800 lbs, wheel base 73.7 in, width 65.5 in) would not require the length or width of a diesel crew cab dually truck(15,000+ lbs loaded, wheel base 149.5 - 169.5 in, width in rear 93 in). Keep in mind there are literally thousands of combinations. I just gave the smallest and largest I would be using this for.

Also it doesn't have to be a cylinder style. It could be any shape. Triangle, square, or rectangular tubing makes no difference to us. But it will have to have a hole drilled through each end to connect to corner pieces.

I found a site for calculating some of this but it might as well be a foriegn language to me.
http://www.atc-mechanical.com/calculators/tube-size-using-structural-properties/#index

Super big thanks in advance for all your help!
If links aren't aloud in threads sorry about that. I didn't know how else to explain everything.

 

[jrmichler]

This is a more of a mechanical engineering project than a physics project. There is a lot more than just sizing the poles. I suggest that you look for a mechanical engineer with experience in steel structures to work with you on this.

I once put together a spreadsheet to do exactly the same calculations, so I know exactly what is involved here. It was for a company that built large machines. They needed to lift machines weighing up to 20 tons with a single crane hook.

I'd like to help you, but it would involve writing a book.

 

[berkeman]

Since this project involves life safety and other potentially dangerous situations, we cannot help you with it. Sorry. As already mentioned, you should seek out a professional engineer in your area who can help you with this.

Thread is closed.

 

[anorlunda]

@jrmichler 's answer was excellent. The question seems to be "How can I do a mechanical engineer's job without understanding mechanical engineering?" We all build things for personal use without the assistance of an engineer. But when it comes to structures or OSHA regulations, a professional engineer is usually needed.

If you design your own lifting rig without an engineer, and if there was a mishap, I suspect that you would have OSHA troubles and that your insurance company would refuse to pay.