Simulation breaking if a PointToPointSpring has sockets on the same body

[itbellix]

Hi @adamkewley, I am running into some weird behavior when I simulate a model with a PointToPointSpring attached. What I am seeing is that if a spring is defined to have its two sockets on the same body, then hitting the Simulate button causes the simulation to break (it is reported as Completed immediately, and the model disappears from the screen. Plots below clarify what I am doing and what I observe, I also attach the model I am using: passive_dynamic_walker_bumps.zip

Spring sockets

Simulation breaking immediately

[adamkewley]

Bug confirmed. Repro:

• Open WalkerModel.osim
• Add PointToPointSpring and set both sockets to Pelvis
• Simulate
• BUG: Model is visible at t = 0 and then disappears at t > 0

This bug is in OpenSim itself, rather than OpenSim Creator. OpenSim should reject a socket assignment like this with an appropriate error message (e.g. Error in PathSpring: body1 == body2 == "/bodyset/Pelvis": you must assign a PathSpring to two different frames) or similar.

[adamkewley]

Closing because this was fixed upstream, which means that it'll percolate for OpenSim Creator sooner or later