Repetitive task therapy is an effective form of rehabilitation for people suffering from the debilitating injuries of stroke. Robotic physical therapy devices have been developed in the past, many of which may benefit from the use of bi-directional pneumatic actuators. This paper presents the Robotic Gait Trainer, an ankle rehabilitation device structurally based on a tripod mechanism with one fixed link. The device incorporates two double-acting, compliant Spring Over Muscle (SOM) actuators as actuation links. The kinematic model of the tripod structure and analysis of the workspace of the robotic device are discussed. It is shown that the device is capable of moving the foot about the ankle joint in dorsiflexion and plantarflexion as well as inversion and eversion, a feature unique to the lightweight, compact and easily portable device. Results of the analysis prove that the tripod structure generates a Range of Motion that matches the safe anatomical range of the ankle joint during gait.