Power and drive
An excavator runs on diesel power because it produces more power and is more robust for heavy work. The motor drives tracks that are similar to tank tracks and hydraulic motors that lift and extend the excavator arm. All power is supplied by the diesel engine, and controls for forward and reverse movement are operated from the control cabin. An operator will use pedals and levers to move the machine back and forth, and to steer the vehicle.
The excavator arm is attached to the bottom of the frame chassis. This arm has three hydraulic pistons with chrome steel piston arms. The arm has two main sections and a bucket loader. The two main sections are articulated with a hinge. One piston is attached to the lower side of the first section and another to the upper side of the second section. When the first piston is extended, the rod pushes against the arm and raises it, extending the section. The second arm contracts or expands, raising and lowering the second section for greater reach. An additional hydraulic piston moves the bucket loader back and forth so the arm can dig and dig.
The tracks are rigid and fixed in place. They are parked around a series of gears that rotate by the power received from the transmission shaft, connected to the motor. When running, the tracks roll the machine forward or backward in a straight line. To turn the machine, one track is brought to a complete stop and the other is started, either forward or reverse. This causes the machine to rotate in an arc. An operator can also put one track in reverse and one track forward to rotate the machine in a tighter circle. This requires two separate transmission systems and a more complicated transmission. Not available on all vehicles. Also, some excavators have a pivoting cab that can rotate 360 degrees. This is driven by another hydraulic motor that is powered by the main motor.