The use of nonlinear Hill-type muscle improves the naturalness of the synthetic motion on the examples of biped28, and research also show that it improves the 2D motion stability for insect simulation33. However the significance of non-linear muscle has not been fully evaluated in the example of a 3D insect model. We here compare the performance of two actuator choices: Proportional-derivative (PD) servo11 and nonlinear Hill-type muscle, in terms of the naturalness of the synthetic motion (Fig. 7). The PD servo is defined as:16\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\tau ={k}_{g}({q}_{t+1}-{q}_{t})+{k}_{d}{\dot{q}}_{t}$$\end{document}τ=kg(qt+1−qt)+kdq˙t\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${q}_{t+1},{q}_{t},{\dot{q}}_{t}$$\end{document}qt+1,qt,q˙t are the rotational angles and velocity of the joint. kg, kd are the gain and damping coefficients.