Tello Leg: The Study of Design Principles and Metrics for Dynamic Humanoid Robots

Abstract

To be useful tools in real scenarios, humanoid robots must realize tasks dynamically. This means that they must be capable of applying substantial forces and also mitigating impacts that may occur during the motion. Towards creating capable humanoids, this letter presents the leg of the robot Tello and demonstrates how it embodies two new fundamental design concepts for dynamic legged robots. The limbs follow the principles of: (i) Cooperative Actuation (CA), by combining motors in differential configurations to increase the force capability of the limb. We demonstrate that the CA configuration requires half the motor torque to perform a jump in comparison to conventional serial design configurations. And (ii) proximal actuation, by placing heavy motors near the body to reduce the inertia of the limb. To quantify the effect of motor placement on the robot's dynamics, we introduce a novel metric entitled Centroidal Inertia Isotropy (CII). We show that the design of state-of-the-art dynamic legged robots empirically reduces the range of CII to improve agility and facilitate model-based control. We hope this metric will enable a quantifiable way to design these machines in the future.

Control and evaluation of a humanoid robot with rolling contact joints on its lower body

“…The evaluation of the design choices presented in Section 2.2 and Section 2.3 is discussed first, followed by the evaluation of the proximal actuation design. The former contains empirical results from our experiments on the robot, while the latter is based on the Centroidal Inertia Isotropy (CII) metric ( Sim and Ramos, 2022 ). Finally, an analysis of the vertical workspace of DRACO 3 is presented to evaluate the benefit of having RCJs.…”

“…When generating the CII values, we chose the nominal configurations such that the robots are in the upright position with their arms fully extended to the sides and their knees bent by 90°. Unlike Sim and Ramos (2022) , in which the test configurations consist of motions of only the hip abduction/adduction and hip flexion/extension joints in the joint space, in order to consider motion primitives in the operational space, we computed the CII values by generating one-step motions in the Cartesian space, where the step length of each robot is normalized based on the robot’s height for a fair and practical comparison across robots. We then obtained the set of test configurations by using inverse kinematics, resulting in a set of 3,000 configurations per robot, and their associated CII values are shown in Figure 6 .…”

“…Another important design consideration on the knee joint involves proximal actuation to achieve agile and dynamic motions ( Sim and Ramos, 2022) . The quantitative evaluation of DRACO 3’s design on proximal actuation is shown in Section 4.1.2 .…”

A Large Force Haptic Interface with Modular Linear Actuators

“…There is no feedback loop using a force/torque sensor. Our approach to open-loop force control has been previously demonstrated in legged robots [30,31].…”

Hands-free Telelocomotion of a Wheeled Humanoid

“…where τ f f = 0 and desired joint velocity are set to zero, qdes = 0. No gravity compensation is added as the design of the upper-body considers proximal actuation design principles [25]. This allows us to assume the arms are nearly massless and contributes to smoothness in arm tracking.…”