During the landing phase the kinetic energy of the moving leg has to be converted. To save energy and use it for the next jump, a spring is needed. The simulation optimized the spring constant to save as much energy as possible. This spring constant is optimized for jumping, so that it can be different for other motions. The translational spring constant can be calculated using the optimal rotational spring stiffness, 350 Nm/rad. The pulley radius has the value 34 mm. This yields a theoretical value of ;#; <latex>\begin{align*} k_t &= \frac{k_{\phi}}{i^2} = \frac{k_{\phi}}{(2r)^2} = \frac{350\:Nm/rad}{(2*0,34\:m)^2} = 75,692 \frac{N}{mm} \end{align*}</latex> ;#; The minimum of the spring stiffness is very flat, so that little differences in the rotational stiffness do not have great influence on the maximum power. Because of that and a small supply of springs with this stiffness and fitting dimensions, the selected spring’s constant is 66 N/mm. It’s an expansion spring of the company Febrotec GmbH.