# Framework for Developing Bio-Inspired Morphologies for Walking Robots
## 2 Framework for Developing Bio-Inspired Morphologies  
A study of bio-inspired morphology begins with the investigation of an animal. As the biologists obtain sufficient functional and mechanistic understanding of the animal's traits, the tasks move from analysis to modelling to synthesis, involving engineers and technicians. To guide this interdisciplinary process, we propose a problem-driven [19] framework for developing bio-inspired morphologies  
Figure 2: The African ball-rolling dung beetle (photo: [PERSON]) (**a**), and the dung beetle inspired robot ALPHA (**b**). for walking robots (Figure 3). The framework uses elements from the hexapod development cycle proposed in [20] while aligning it with other bio-inspiration processes [19; 21] and integrating tasks related to studying and analysing the biological subject. Thereby, the framework's structure matches other bio-inspiration models described in [19], but also details the specific objectives related to the development of bio-inspired morphologies for walking robots. This has four phases: 1. Biological model, 2. Design, 3. Implementation, and 4. Analysis. The first one primarily involves trained biologists, while the last three involve trained engineers; however, some overlap does occur in-between. In phase (1. Biological model), the morphological data of a selected animal species are collected for engineers to use in the later design phase. The phase starts with selecting a species that is known to have features of interest for modelling and/or further study (1.1) The selection is based on the aim to (a) investigate specific features of the animal biomechanics, locomotion, behaviour, etc., which are desirable to implement in robots, or to (b) investigate a biological hypothesis by using a physical robot model. Next, the feature(s) of interest to investigate is selected based on a desirable trait for a robot (1.2). Subsequently, multiple specimens of the selected animal species are measured (1.3). Different techniques can be deployed such as measuring joint positions with a 3D microscope [15], CT scanning the animal [4] or measuring the weight of individual segments [15]. Phase 1 finishes by describing the kinematics of the animal (1.4). This is done by converting the raw surface model into an articulated 3D model or transcribing the degrees of freedom in a kinematic chain with dimensions. Figure 3: Framework for Developing Bio-Inspired Morphologies for legged robots with four phases: 1. Biological model, 2. Design, 3. Implementation, and 4. Analysis. As mentioned above, it is necessary to measure multiple specimens to average the dimensions and to counter other variabilities among specimens (e.g., gender, age, injury). In phase (2. Design), the biological model is used to guide the design of a robot model. The phase begins by developing a conceptual design of the robot with a focus on the desired features (2.1). The next step, Adjustment (2.2), identifies the features of the biological model that are not feasible and essential to recreate in the robot's morphology. Thereby, 2.2 highlights unavoidable deviations between the biological model and robot, or rather, _adjustments_ of the biological model for it to fit all robot components. For example, increasing the size of the transcribed morphology (1.4) might be necessary to fit all hardware components (2.3) and to place the actuators according to the joint axes. Finally, the robot's hardware and materials are chosen (2.3). Critical to this phase is the close collaboration between biologists and engineers. This depends on the engineer learning enough about the biology and the biologist learning enough about engineering requirements and limitations to understand the fine details of the project, tasks with an often underestimated time consumption. In phase (3. Implementation), engineers and technicians develop, construct, and assemble a prototype of the final version. The first step is to optimise the design (3.1), for example, to reduce the robot's weight and the actuators' load.