These units have rotating articulated knuckle booms which allow for reaching up and over obstacles. They are self-propelled, are driveable at full elevation and are used primarily in indoor and slab applications. Their small footprint allows for access in confined areas with little or no tailswing. They are powered by batteries which are recharged from standard 220v outlets, making them silent and emission-free. Stability is achieved by means of counterweights and tilt sensors.