The first is to move forward at a predetermined velocity ν* of body center (a vector pointing straight forward):11\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${f}_{v}=\sum _{k}{(\nu -{\nu }^{\ast })}^{2}$$\end{document}fv=∑k(ν−ν⁎)2where ν is the actual moving velocity of body center. The subscript k sums up all the simulation steps. The velocity is three dimensions (x, y, z) thus this objective function also penalizes the case when the body falls down or deviates from the forward direction.