The high speed, high accuracy control of DD systems requires the full system a dynamic effects it be taken into account in the control design, due to the eliminated gear mechanism, and hence, the increased effect of structured or unstructured uncertainties between the motor and load The actuator dynamics and structural flexibilities become of increased importance particularly when high speed, high accuracy operation of lightweight DD structures is aimed However, most related studies on DD robots neglect these effects concentrating only on link dynamics hence compromising the tracking accuracy in the transient and steady state. On the other hand, the actuator dynamics and/or torque ripple is taken into consideration only in relation to the high performance control of DD motors. This paper aims for the high accuracy, high speed control of direct-drive (DD) robotics systems via novel robust high-order sliding mode controllers (HOSMCs) of 2nd order (2-HOSMC), and 3rd (3-HOSMC), designed and experimentally tested on a single link arm under uncertain gravity effects. Two novel 3-HOSMCs are designed, both with the simultaneous consideration of the actuator dynamics, torque ripple, and structural flexibilities to address the above mentioned problems with DD systems. This is one of the contributions of the paper to existing literature, where HOSMCs are derived by artificially increasing the system order, creating additional needs for integration. To avoid the excitement Of internal dynamics and to increase accuracy, one of the HOSMCs is also designed and tested with continuous input, which is another contribution of the study. The performances of the novel HOSMCs are tested experimentally on a hardware-in-the-loop (HIL) simulator test-bed, developed for a I degree-of-freedom (DOF) direct-drive (DD) flexible link arm (FLA). The experiments performed under load variations and external disturbances reveal the superiority of the designed new 3-HOSMCs, especially that of the continuous input HOSMC, in terms of improved tracking accuracy and reduced torque ripple effects, motivating the use of such controllers for demanding high performance control applications under heavy uncertainties. Copyright (C) 2009 Praise Worthy Prize S.r.l. - All rights reserved.