Abstract: More accurate and efficient robotic systems highglight the importance of the drive systems of robot manipulators. The drawbacks with the traditional methods of power transmission include friction, backlash, and compliance. To overcome problems of this kind, the concept of direct drive (DD) was introduced. In This type of transmission the shaft of the motor is directly coupled to the joint of the manipulators, causing a noticably lower payload. So the necessity of existence of an intermediate element to provide relocation, led to a new kind of transmision called direct transmission (DT). It benefits higher performance than DD but it causes some limitations over the mobility of actuators. The common SISO control techniques are no longer applicable to deal with the high level of dynamic complexity - such as coupling and nonlinearity. This problem can be resolved using more advanced control methods like model-based or computed torque control. The other method to reduce this complexities was to redesign the manipulator. Vines proposed nonlinear drive transmission which has the advantages of DT and reduction ratio properties of gearboxes. It has very little friction, backlash, and compliance compared to the traditional methods, while providing actuator relocation, directness of DD, and a varying reduction ratio.