Closed kinematic loops

[Rory Turnbull]

Hi All,

My project involves looking at how exoskeletons and the body interact. As part of this, I have produced a closed kinematic loop with the two chains connected by a point constraint at the ankle joint.

The model has built on the SCONE example 4a lower limb model and I was hoping that I would be able to use the same control system and weightings. However, when I attempt to load the updated model into SCONE it gives the following error:

Error creating resource: Invalid point constraint body1 () specified in Constraint PinL

I have double-checked and it looks like the point constraints are fully aligned and they don't produce any accuracy errors when running the model through the visualiser. Is this an issue with SCONE and it not liking point constraint/ closed kinematic loops? or is it more likely an issue with how the constraints are set up?

When opening the model within the OpenSim GUI it is acting as I would expect it to.

Best wishes,
Rory Turnbull

[Thomas Geijtenbeek]

Hi Rory,

Did you by any chance edit the model using OpenSim 4? At this moment, OpenSim 4 models are not officially supported in SCONE (even though this may change soon).

If you are able to load and simulate your model in OpenSim 3, then it should also work in SCONE, since they both use same API. Please let me know if this is the case.

[Rory Turnbull]

Hi Thomas,

Thank you for your response and sorry for the delay in reply.

I did create the model using OpenSim 4, do you know when SCONE might start supporting it?

Since seeing your response I have been trying to build the equivalent model in OpenSim 3.3 but have had difficulty (I have been posting in the general OpenSim forum to try and get help with it).

Best wishes,
Rory Turnbull

[Thomas Geijtenbeek]

Support for OpenSim4 is available in the SCONE 2.0 BETA release, which currently is only available at:

https://hyfydy.com/downloads/

To use OpenSim4, be sure to replace "ModelOpenSim3" with "ModelOpenSim4" in your .scone file.