Retractable Wheels 1

[CProteusS]

I am designing an A-frame structure that needs to be capable of rolling on a concrete surface, but that has a the ability to retract or fold the wheel into the hub when it is loaded onto a flatbed truck.

The A-frame structure will weight approximately one ton and the load will weight approx. 15 tons. I can use steel casters. The structure is unidirectional and will be pulled with a forklift.

I can send a pic if it helps.

 

[CRG]

What is the question?

 

[CProteusS]

I want to know if it's feasible to use a folding wheel design that will allow me to have the wheels drop down when the framework is lifted off the truck (not unlike landing gear) and develop a mechanism for retracting the wheels when it is placed on the truck? An alternative method would be to use retractable wheels that could be lowered through the framework when moving on concrete and retracted when it is placed on the truck.

My question is whether this type of design could work under the type of load that I'm talking about. I'd like to avoid hydraulic or air lifts, if possible, and stick with a lever to retract or fold the wheels.

 

[griffengm]

CProteusS,
Can the wheels be retracted one by one or all at the same time?
One or maybe two at a time could be done manually with a scissor jack arrangement.
Simultaneously with a mechanical linkage could be a challange if there are no lower members joining the two A-frames(I make the assumption that there is one at each end of an overhead beam). There are some manual hydraulic systems that might do what you want but I do not remember the name at the moment.

Griffy

 

[Hydroformer]

Is the A frame intended to transport loads or just to be wheeled into position then lift ?

Our "die horses" are on spring loaded casters. With no load on the horse, the wheels are down and the horse is mobile. Once loaded, the wheels are pushed up and the foot touches down supporting the load.

By carefully tuning the spring rate to the unladen mass of the frame the wheels can be retracted with minimal loading (ie. tie downs on the flatbed).

regards,

Hydroformer

 

[Barry1961]

You could use caster jacks like used on boat trailers. McMasterCarr has them.

http://www.mcmaster.com/

Search for 8149T51, it is a little oversized but you got to count on hitting a few pot holes now and then.

Barry1961

 

[CProteusS]

The A-frame will be used to transfer up to 35,000 lbs of marble and granite to the truck. Then it will be lifted onto the flatbed and lowered onto the bed. The reason it has to be flat is that if the marble is not securited bedded down, any slight twisting moment on the slab could result in a fracture.

 

[hendie]

I worked in the marble industry for a number of years. Whenever we transported marble/granite, it was always on an "A" frame on the back of the truck and strapped down. Whenever we imported it from the quarries, it was always strapped onto "A" frames in the containers.
We would never have considered transporting marble or granite "flat" (or have I misunderstood your post ?)

 

[MikeHalloran]

If the casters were spaced more than 8 ft inside to inside, then they could straddle the truck bed, and a cross- beam could rest on the bed and support the a-frame. That, however, would constitute a 'wide load', and you'd need to make special arrangements to move the truck, etc.

That idea could work if you were exclusively using trucks with skeletal payload areas, e.g. timber haulers, instead of flatbeds, or if the flatbeds had big holes for the casters to drop into. E.g., you'd need control of the trailer fleet, which you probably don't have.

Let's assume that whatever mechanism you use to fold the casters will drop into a vertical position when the a-frame is supported by a crane. That in itself requires careful attention to working clearances and friction in a hostile environment, but let's assume it can be made to happen.

From there, I can imagine a set of small 'pilot casters' that hang below the big ones, and as the assembly is dropped onto a platform, run out laterally beyond a trailer's width and somehow cause the big casters to be engaged in rigid fashion under the a-frame. If lowered onto a trailer bed, said pilot casters would fall of the edges, and somehow cause the big casters to swing into a non- supporting position. Then, as the load is lowered onto the static stops, the pilot casters are somehow swung back inboard, so they don't project beyond the edges of the trailer.

Now, I have a problem; an eidetic mind. I can envision things that never were, and things that can't possibly work anyway, so you'd have to screw around with mechanisms for a while to _maybe_ come up with something that could meet that spec.

But I wouldn't bother, because I'm assuming that this mechanism has to be trusted by, and therefore understood at a glance by, stonecutters. I'm sure there are many fine mechanism designers hidden within the stonecutter community, but I can't imagine it being a job prerequisite, so it's a skill that's likely unexercised there.

I.e., if your assembly has moving parts, they have to be, pardon the expression, as simple as a stone.

So I'm thinking the casters could be attached to 'elephant feet', short pieces of fat square steel tube, that slide easily over some slightly longer, smaller, pieces of tube projecting vertically downward from the a-frame. Put some vertical slots in the elephant feet, and a sturdy cross- pin to keep them from falling off entirely.

Got the picture? As the assembly hangs from the crane, the feet with casters hang straight down below it. To make it suitable for ground transport, four laborers guide the smaller tubes into the larger tubes as the assembly descends, until the tubes are fully engaged with each other.

To put the assembly on the trailer, four laborers simply push the casters aside, so the elephant feet fold inward as the assembly is lowered to rest on the end of the shorter tubes. Of course, the unslotted sides of the big tubes have to be cut away near the top so the tubes can swivel and the small tube can travel right through the upper end of the big tube. The slotted faces of the big tubes just rotate around the upper end of the slot.

I'll think of something simpler after you've committed it to production. ;-)






Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ornerynorsk]

Look at the carriage and trails design of the M2 155MM howitzer. This might be of help.