# Framework for Developing Bio-Inspired Morphologies for Walking Robots
## 4 Phase: Design
### Conceptual Design of the Robot  
Prior to modelling the robot, it is essential to establish a component and material architecture (Section 4.3) optimized for the robot design. For example, the walking robot's size, shape, dynamics and assembly are, to a high degree, shaped by their actuation system and the torque density [23]. Additionally, structural materials and components are chosen to have high strength and stiffness, while maintaining a small size and mass, in order to minimize leg inertia and to improve the overall dynamics [23]. Hence, the selected components influence the conceptualization of the robot.  
Laser-cut sheet metal and composites are an optimal mechanical framing system for the robot, as they are cut to exact sizes, quick to produce in-house, and therefore enable swift investigation of various ideas and prototypes. Using sheet materials requires three-dimensional parts to couple thesheets together with spacing in between, in order to gain stiffness and reproduce the joint angles of the biological model.  
Three versions of the robot were constructed to obtain a feasible and robust design: a mock-up (I), a functional model (II) and the _ALPHA_ prototype (III). The mock-up is based on crude dimensional assumptions and was rapidly constructed to obtain a physical reference model for insight in the robot size and design challenges. It consisted of 4-mm, laser-cut plywood and 3D-printed couplings that could attach the plywood pieces at correct angles to create an enlarged version of the biological model.  
The functional model tested if it matched the scaling factor [22:1] of the biological model (Section 4.2) can hold all the pre-selected components while still allowing full mobility of the spinal joints and legs. The scaling factor was multiplied with the transcribed kinematics of the biological model (Section 3.4) to obtain the robot's dimensions. Subsequently, Autodesk Inventor and the add-on PointLinker by CoolOrange was used to import the enlarged dimensions from Excel into the CAD files. The imported dimensions then defined the shape of the frame, legs and joint couplings (Figure 5). Laser-cut, 3-mm aluminium sheets, carbon fibre tubes, and 3D-printed motor replicas and couplings (Section 4.3) were used to create the functional model.  
The functional model's precision in recreating the biological model (Section 3) was evaluated by first comparing (I) the legs' kinematic _origin points_ in relation to the scaling factor and (II) the angles of the TC and AC joints (Table 1) where the the origin points is defined by the coordinates for the intersection of TC and CTF joint axes. Hence, the functional model's dimensions matches those of the _S. galenus_ (Table 1), with the exception of the front legs' CTF joint position (Section 4.2). The lengths of the leg segments were compared separately.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**ALPHA**} & \multicolumn{4}{c}{_Scarabaens galenus_} \\ \hline Deg & hind & mid & front & hind & mid & front \\ \hline \(\phi\) & 52.0 & 31.0 & 54.0 & 51.0 & 31.0 & 53.8 \\ \(\theta\) & 38.0 & 38.0 & \(-\)43.0 & 38.0 & 38.0 & \(-\)43.0 \\ \hline mm & hind & mid & front & hind & mid & front \\ \hline x & 0.0 & 106 & 296.6 & 0.0 & 4.8 & 14.4 \\ y & 43.9 & 44.0 & 21.9 & 2.0 & 2.0 & 1.0 \\ z & 0.0 & \(-\)10.5 & 45.1 & 0.0 & \(-\)0.5 & 0.4 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Leg configuration of ALPHA and _S. galenus_. Dimensions are specified in degrees and mm. The scaling factor of [22:1] between the ALPHA and _S. galenus_ is noticeable in the dimensions.  
Figure 5: Dimensions of the developed concept for a bio-inspired robot morphology (Section 4.1) that is based on the dimensions of the dung beetle (Section 3.4). The leg-mounting configurations with a top view of the functional model and ALPHA with (a) transverse dimensions and mounting roll angles [\(\phi\)] for each pair of legs, as well as (b) a side view with midsagittal dimensions and pitch angles [\(\theta\)].