nAdd a Frame body to the model. If you are using Transient Structural and not Explicit Dynamics, you can change the behavior to Rigid.nAdd a Translational Joint to Ground on the Frame Body. This is what keeps the Frame level as one of the four legs makes impact.nAdd a Rotational Joint between the top link in the leg and the Frame Body. This allows that link to rotate relative to the Frame. You might want to add a Rotational Spring into the Joint Definition as there are usually springs in landing gear.nWhat do you have between the two links of the leg? That might also be a revolute joint with a spring.n