Some machines, since 1998 now use a direct drive motor, a low aspect ratio device, where the stator assembly is attached to the rear of the outer drum, whilst the co-axial rotor is mounted on the shaft of the inner drum. Direct drive eliminates the need for a pulley, belt and belt tensioner. It was invented by LG Electronics in 1998 and patents were granted in the US in 2010. Since, other manufacturers have followed suit. Some washing machines with this type of motor now come with 10-year warranties. The direct drive motor's rotor is outside the stator as this provides a slim motor with speed reduction and torque multiplication. The rotor is connected to the inner tub through its center. It can be made out of metal or plastic.