I written a general idea on forklift arms in [forums.reprap.org]

However I thought a specfic idea similar to above could apply to deta robots.

Notice how some forklifts could lift twice it's height? Well what if we replace the sides with a forklift mechanism, such that the delta robot could print twice its height (Or triple the height, with the right mechaism)

Pros: More compact form for delta robot, prints twice its height.

Cons: Potentially slower printing speed due to more mass needed to move.

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Some consideration: with 3 extra motors, the 'cons' above could be alleviate by making the movement of the 'forklift' arms independent of the 'printing arms'. This reduces the 'moving' mass, and thus will improve speed.

The problem with 3d printing is that you need to be precise. Your idea is conceptually good. The challenge is now how do we do that cheaply and precisely. The way I am looking at it, every stage you add to the forklift mechanism will add 2 smooth rods and 4 linear bearings. You can quickly see that the vitamin count will get out of hand. In many cases, scaling up an existing design to get a big print volume is the cheapest solution. The benefit of your idea would be that you could possible make a compact robot.

If you like this idea and want to see it happen, I encourage you to run with it.

I indirectly work with forklifts, the biggest issue I can see is that they tend to be hydraulic lifting, and gravity descent, which may not be ideal, and there may be issues with the y direction stability if it's single sided, depending on the overall mass. the concept has possibilities, but fork lifts by their nature and because of safety are usually massively over engineered in the mast area, to make sure that nothing is going to fail even if somewhat overloaded. A triple lift mast, which is the normal for higher lifts, will also flex forward at higher extensions due to the tolerance of the bearings, it's not much, but for the accuracy needed for printing, it will be an issue, it might be possible to overcome it in firmware, but that's then another variable that has to be calculated and allowed for across the entire travel range.

Some of that play is taken out by rubbing strips, which will add in friction, which is not ideal, in a forklift, it doesn't matter, but again, for a printer, that's not ideal, as it might also then cause problems with the descent phase. A 3 stage lift mast has a lot of lift chains so that all 3 sections lift proportionally, but only after the first stage has lifted completely, which is related to being able to operate inside containers without hitting the roof, which is a complication that would not be needed in the same way for a printer. The other issue then would be that the hydraulic cylinders are multi stage, so there would be some challenging issues with the stepping of each stage of the ram, especially over the transition

So, while the concept has possibilities, I suspect that there's going to be easier ways of achieving what you're looking for

Interesting idea. I also think we can use 4 crawler cranes / construction cranes like this : [www.bnpeters.com]
and at the center platform take one robot arm from this : [gigaom.com]
It is complicated but I think it have potential to be another technique we build skyscraper in near future, for high budget project.