# A Review of Foot-Terrain Interaction Mechanics for Heavy-Duty Legged Robots
## 2 Supporting Feet of Heavy-Duty Legged Robots
### Spherical Supporting Foot Configurations
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Robot** & \begin{tabular}{c} **Length \(\times\) Width \(\times\)** \\ **Height (m3)** \\ \end{tabular} & **Legs** & **Foot Shape** & \
\begin{tabular}{c} **Driving** \\ **Method** \\ \end{tabular} & **Mass (kg)** &
\begin{tabular}{c} **Payload** \\ **(kg)** \\ \end{tabular} & **References** \\ \hline TITAN XI & 5.0 \(\times\) 4.8 \(\times\) 3.0 & 4 & Cylindrical & Hydraulic & 6800 & 5200 & [16] \\ TITAN IX & 10 \(\times\) 16 \(\times\) 5.5 & 4 & Cylindrical & Electric & 170 & - & [17] \\ TITAN III & - & 4 & Cylindrical & - & 80 & - & [18] \\ COMET-IV & 2.8 \(\times\) 3.3 \(\times\) 2.5 & 6 & Cylindrical & Hydraulic & 2120 & 424 & [19] \\ Dante II & 3.7 \(\times\) 2.3 \(\times\) 3.7 & 8 & Cylindrical & Electric & 770 & 130 & [20] \\ NMIIIA & 1.5 \(\times\) 0.5 \(\times\) 1 & 6 & Cylindrical & Electric & 750 & 80 & [1] \\ SILO 4 & 0.31 \(\times\) 0.31 \(\times\) 0.3 & 4 & Cylindrical & Electric & 30 & - & [21] \\ ESpider & 1.9 \(\times\) 1.9 \(\times\) 1.0 & 6 & Cylindrical & Electric & 300 & 155 & [22,23] \\ Octopus Robot & 1.5 \(\times\) 1.5 \(\times\) 1 & 6 & Cylindrical & Hydraulic & 200 & 200 & [24] \\ Hexapod Robot & - & 6 & Cylindrical & Hydraulic & 3000 & - & [30,31,32] \\ Legged Robot & - & 6 & Cylindrical & Electric & 4200 & - & [33,34] \\ Big Dog & 1.1 \(\times\) 0.3 \(\times\) 1 & 4 & Semi-cylindrical & Hydraulic & 109 & 50 & [25,26] \\ MBBOT & 0.85 (Height) & 4 & Semi-cylindrical & Hydraulic & 140 & - & [40,41] \\ HexbotIV & 1.0 \(\times\) 0.72 \(\times\)1 & 4 & Semi-cylindrical & Hydraulic & 268 & 50 & [43,44] \\ LS3 & 1.7 (Height) & 4 & Semi-cylindrical & Hydraulic & 590 & 182 & [45] \\ ScalI-I & 1.0 \(\times\) 0.4 \(\times\) 0.68 & 4 & Semi-cylindrical & Hydraulic & 65 & 80 & [46] \\ ScalI-II & 1.1 \(\times\) 0.45 & 4 & Semi-cylindrical & Hydraulic & 130 & 140 & [47] \\  & (Length \(\times\) Width) & 4 & Semi-cylindrical & Hydraulic & 200 & 200 & [48] \\ Space Climber\({}_{1}\) & 8.2 \(\times\) 10 \(\times\) 22 & 6 & Special & Electric & 185 & - & [49] \\ Space Climber\({}_{2}\) & 8.5 \(\times\) 10 \(\times\) 22 & 6 & Spherical & Electric & 23 & 8 & [50] \\ TITAN XIII & 2.134 \(\times\) 5.584 \(\times\) 3.4 & 4 & Spherical & Electric & 5.65 & 5.0 & [51,52] \\ SCOUT II & 0.55 \(\times\) 0.48 \(\times\) 0.27 & 4 & Spherical & Electric & 20.86 & - & [53] \\ SILO 6 & 0.88 \(\times\) 0.45 \(\times\) 0.26 & 6 & Hemispherical & Electric & 44.34 & - & [54] \\ SDU Hex & 0.98 \(\times\) 0.4 \(\times\) 0.1 to & 6 & Hemispherical & Electric & 35 & - & [55] \\  & 0.6 & & & & & & \\ Landmaster & 3.6 \(\times\) 2.3 \(\times\) 2.6 & 6 & Square & Hydraulic & 3950 & 1000 & [1] \\ Landmaster 3 & 1.4 \(\times\) 1.3 \(\times\) 1.0 & 6 & Square & Electric & 82 & 30 & [1] \\ Petman & 1.5 (Height) & 2 & Square & Hydraulic & 80 & - & [56] \\ Altas & 1.8 (Height) & 2 & Square & Electric & 150 & - & [57] \\ Charlie & 8 \(\times\) 4.4 \(\times\) 5.4 & 4 & Special & Electric & 21.5 & - & [58,59] \\ Walking Truck & 4 \(\times\) 3 \(\times\) 3.3 & 4 & Special & Hydraulic & 1300 & - & [60] \\ TITAN VII & - & 4 & Special & - & - & - & [61] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Published performance indicators for heavy-duty legged robots with passive adaptive joints. Figure 22: Foot configurations with passive adaptive joints for different heavy-duty legged robots. In terms of configuration, the cylindrical shape is symmetrical in all directions, which can make the normal and the tangential forces on the robot's supporting feet more uniform. The robot's foot slip is effectively suppressed. It plays an irreplaceable role in the movement of heavy-duty legged robots on unstructured terrain. The cylindrical foot has a larger contact area with the terrain, which is compared to the smaller contact area of other feet. For the heavy-duty legged robots, increasing the area between feet and terrain in the process of operation can reduce the pressure on the foot per unit area and improve the support effect during the load-bearing period.