Pithivier57 is a French AFOL, who also decided to build a remotely controlled LEGO TECHNIC excavator. It is an 80 ton. CASE CX800 machine.
There are some PF motors on-board to move the undercarriage and rotate the cab, while the boom, dipper and bucket are operated by pneumatic cylinders.
On the remote unit there is a PF IR remote, to control the excavator undercarriage motors, and two additional PF M-motors for a compressor that feeds the model pneumatics, via a few umbilical pneumatic tubes.
Main point of interest of this excavator, are their unique and extra long pneumatic cylinders custom made by the author.
It is a characteristic from large size excavator TECHNIC models, to require long cylinders well above those produced by LEGO. While long ago some other builders have solved the problem of not having appropriate LEGO cylinders off-the-shelf, using ropes and dummy cylinders [1, 2], many others (LEGO inclusive ) have used the standard ones in a back-to-back setup to double their operative length. However, achieving this way a functional but quite unrealistic solution.
This is the point where some innovative minds, decide to go for customized solutions. And so Pithivier57 did also .
When I first saw this excavator videos, immediately remembered to have seen similar custom pneumatic cylinders before, made by someone else, somewhere...
After some searching got to find it again, at Jan Groen Brickshelf folder together with an explanation on how he did it. 
These seem to have been done in a very similar way, to what Pitihvier57 might have done too!?
There might be also a similar custom cylinders solution, on Anders Gaasedal's Volvo Excavator [6, see it also at TBs updated Excavators "Hall of Fame" post], but it is still not clear for me and I'm waiting on Anders' feedback on this subject.
Have meanwhile just realized , that Anders turned LEGO Designer in between [btw a TECHNIC designer (Goose Valley)], so it makes very unlikely to get an answer with further details about the cylinders. But on the other way it would make our chances to get a decent official TECHNIC Excavator with longer pneumatics in the future, somehow more likely...
Last Update: 2009.Sep.03 12:29 GMT
Main issue we can easily observe from Pithivier57's videos [7, 8, 9], are the cylinders sudden movements which may also look a bit unrealistic as it is the usage of pneumatic cylinders itself.
In fact this is an effect that may only get worse, as the longer the cylinders get.
In real life, such machines use hydraulic systems instead of pneumatic ones. They are a lot more powerful and work much smoother. However it is very unlikely that we ever come to see something similar by LEGO.
Thus one chance could be to play a bit with advanced pneumatic control solutions, that would allow to control the air flow into the cylinders and stopping the cylinders in the middle for digger action. Just like those developed by Mark Bellis years ago, and of course if there is any room left inside the model to accommodate it all.
As you may expect, several other photos from this CX800 excavator can be found at the author's BS folder too.