I uploaded a video to Youtube which shows new joint mechanics that have been added in the last couple of releases. Joints in MOMDYN combine attributes of various features of the classic interface. A revolute joint creates a new frame along with the associated symbolic constants and time varying properties. A prismatic joint creates a vector and point. Each can include spring-damper physics, which is included in the demo.
The example shows the creation first of a simple pendulum, then of a pendulum with mass attached to a translational spring-damper. A keen observer may note the frequency-doubling effect in this dynamic system; when the pendulum is near the bottom the centripetal acceleration (r ω^2) is highest, and therefore the spring will get extended. This happens twice per cycle of the pendulum oscillation, thus the doubling of the pendulum frequency. The translational mode frequency at about 1 Hz is also pretty distinct. So, two degrees-of-freedom but three frequencies, kind of neat and nonlinear I say.
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