In robotic actuators, low speeds and high torques are usually required. Small electric motors, which are more efficient at high speeds and low torques, do not fit the requirements directly. In order to transform the motor characteristics into the desired output characteristics, a transmission system is needed. Ideally, it should be optimally designed and adapted to the desired characteristics and the available space. Scaling laws can provide a way to design these desired output requirements as a function of the size parameters. These are however not yet available for transmission systems. To fill this gap, several scaling laws are developed throughout this paper for some of the most important robotic characteristics, i.e. maximum continuous output torque and reflected inertia, in function of the number of stages, the transmission ratio and the size parameters of different types of transmissions. These laws show that diameter has a much bigger influence on the characteristics of transmissions than length. All derived laws show good comparison with catalog data of manufacturers like Maxon, Moog, Neugart, Harmonic Drive , Sumitomo and SKF.

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With the growing popularity of Human–Robot Interactions, a series of robotic assistive devices have been created over the last decades. However, due to the lack of easily integrable resources, the development of these custom made devices turns out to be long and expensive. Therefore, the SMARCOS, a novel off-the-shelf Smart Variable Stiffness Actuator for human-centered robotic applications is proposed in this paper. This modular actuator combines compliant elements and sensors as well as low-level controller and high-bandwidth communication. The characterisation of the actuator is presented in this manuscript, followed by two use-cases wherein the benefits of such technology can be truly exploited. The actuator provides a lightweight design that can serve as the building blocks to facilitate the development of robotic applications.