The cost of transport (COT) is a highly informative parameter that characterizes the mobility performance of the vehicle, and is especially useful when comparing one vehicle to another. Therefore, the COT distribution of CASPER was calculated so that the optimal settings for mobility performance could be identified. The cost of transport is defined in Equation \ref{eq_COT} below, where \(P\), \(W_c\), and \(V\) are the craft power, weight, and velocity, respectively.
\[COT\ =\ \frac{P}{W_{c\ }\cdot V}\begin{equation}
COT = \frac{P}{W_c\cdot{}V}
\label{eq_COT}
\end{equation}#\left(1\right)\]
Generally, Figure \ref{700640} shows that the cost of transport reduces as the RPM increases, and that the COT is not significantly impacted by load time. Comparing the top and bottom rows of Figure \ref{700640}, it is clear that the narrow/wide configurations have roughly the same cost of transport at all angular velocities and load times. From these graphs, it can be concluded that cost of transport is minimized (or that the mobility system is most efficient) when the screws are operating at high angular velocity. This implies that they move the fastest for a given amount of power, and thus are more efficient for mobility in granular media. In the next section, the cost of transport and excavation rate will be investigated simultaneously to quantify the mobility and excavation performance as a whole. Conveniently, the excavation system is also most effective when operating at high screw angular velocities. It is critical for a screw-propelled excavation to operate in the configuration that minimizes the cost of transport, because screws present an inherent disadvantage to wheels and tracks when travelling in the counter-rotating mode during the excavation process.
Excavation Transport Rate