Walking excavator

A walking excavator or popularly spider excavator is a special type of all-terrain excavator. Like the regular excavator it consists of a boom, stick, bucket and cab on a rotating platform known as the "house". However, its house sits atop an undercarriage consisting of leg or arm-like extensions with or without wheels. All extensions can move in increments, hence the name "walking excavator". This is different from an early 20th century dragline excavator where a set of feet plate are alternately lifted and lowered.
History.
Most traditional excavators have tracks or wheels as undercarriage which limits their usability on steep inclines, uneven terrain or inaccessible positions.
In 1966, Edwin Ernst Menzi (1897–1984) and Joseph Kaiser (1928–1993) together invented the walking excavator for work on mountain slopes. Subsequently, Kaiser AG, Schaanwald, Liechtenstein, and Menzi Muck AG, Kriessern, Switzerland, developed separately excavators.
Despite the advantages of the design it failed to be widely used due to little gain in mobility, considering most work are in urban areas, less comfort, expensive design plus expensive electro-hydraulic control and maintenance.
In addition, the walking excavator is still not so well known to the general public.
Today, only walking excavators and forest harvester, like the Ecolog forest harvester or the TimberPro tilt cab are truly designed to move and work in mountains.
Economic success.
In 2007, Kaiser AG, Schaanwald, Liechtenstein, realized a turnover of nearly 60 million Swiss francs.
In 2013, Menzi Muck AG had a turnover of 56.93 million Swiss francs.
In 2014, Kaiser AG had a turnover of 70 million Swiss francs.
Design.
The walking excavator's main feature is the ability to move in a crab- or spider-like fashion and hence overcome any terrain obstacle. The undercarriage design varies widely from model to model and between specialized roles. The number of legs or wheels can also vary from e.g. three (Menzi Muck 5000T2) to four. The "leg" design can also vary from fixed to telescoping arms. Most modern walking excavators have rotating or powered wheels allowing them to roll or drive depending on the need.
Scenario.
Often the boom is also employed in moving for example to overcome wide gaps larger than the reach of their "legs".