Nick Petit
npetit
About Me
Connect
LOCATION
Not Specified
WEBSITE
Houdini Skills
Availability
Not Specified
My Badges
SideFX Staff
Since Feb 2008
Recent Forum Posts
Keyframing Glue strength not working July 10, 2025, 5:10 a.m.
The global constraint parameters (under Advanced > Constraints) set the base values for the constraints. The attributes on the constraint primitives are multipliers of those base values (except for some parameters where scaling the parm values doesn't make sense, i.e toggles, integers, and directions or axes). This is documented under each bullet constraint type.
By default the constraints are initialised with whatever attributes they have at the start of the sim. If you want to update those attribute, you need to enable "Override Attributes" and specify the attributes to update.
If you have a strength attrib value in the range 5,000-10,000 and then set the global glue strength to 1000, you now have constraints that have strength ranging from 5,000,000 to 10,000,000 (they'll be very hard to break) - the reason why all those global parm values default at 1 is so they have no effect on your constraint attributes by default as you can achieve much more plausible results by using the attribute values that vary across all the constraints, which is done easily using the RBD Constraint Properties SOP, rather than having them all set globally to the same values.
The attribute names to use in the Override Attributes string field refer to attributes on the constraint geometry - not parameter names. Generally, the attributes are specific to each constraint type and documented in the help for each bullet constraint type. The RBD Constraint Properties and RBD Cone Twist Constraint Properties SOPs set all those attributes up for you.
But you may want to update your own animated attribute that you want to use in a VEXpression or a SOP Solver during the sim to control localised breaking of constraints for example - a typical example would be to do an attrib transfer of Cd attrib and break or weaken some constraints when they turn red for example.
I hope that helps clarify things somewhat!
By default the constraints are initialised with whatever attributes they have at the start of the sim. If you want to update those attribute, you need to enable "Override Attributes" and specify the attributes to update.
If you have a strength attrib value in the range 5,000-10,000 and then set the global glue strength to 1000, you now have constraints that have strength ranging from 5,000,000 to 10,000,000 (they'll be very hard to break) - the reason why all those global parm values default at 1 is so they have no effect on your constraint attributes by default as you can achieve much more plausible results by using the attribute values that vary across all the constraints, which is done easily using the RBD Constraint Properties SOP, rather than having them all set globally to the same values.
The attribute names to use in the Override Attributes string field refer to attributes on the constraint geometry - not parameter names. Generally, the attributes are specific to each constraint type and documented in the help for each bullet constraint type. The RBD Constraint Properties and RBD Cone Twist Constraint Properties SOPs set all those attributes up for you.
But you may want to update your own animated attribute that you want to use in a VEXpression or a SOP Solver during the sim to control localised breaking of constraints for example - a typical example would be to do an attrib transfer of Cd attrib and break or weaken some constraints when they turn red for example.
I hope that helps clarify things somewhat!
How to setup RBD Car Follow Path node in DOP context July 10, 2025, 4:49 a.m.
There is a RBD Car Follow Path DOP which handles this for you.
You can dive inside to see how it's setup.
The problem you're having is you need the SOP Solver to use the invoke compiled block option so you can operate on both the geometry and the constraint geometry at the same time. Use a SOP Solver (Constraint Geometry) DOP - this sets it up for you.
You can dive inside to see how it's setup.
The problem you're having is you need the SOP Solver to use the invoke compiled block option so you can operate on both the geometry and the constraint geometry at the same time. Use a SOP Solver (Constraint Geometry) DOP - this sets it up for you.
How to setup RBD Car Follow Path node in DOP context July 9, 2025, 7:45 p.m.
That's a switch that is only useful for when the node is used in a SOP Solver used as a pre (or post) solve for a rigid body solver in DOPs.
When this is enabled, it only snaps the car in position at the first frame of the sim (or whenever the car appears in the sim), and from there the car's current position, advected by the sim, is used to calculate where it wants to be and how it should get there by adjusting attributes on the steering conetwist constraints and the hard motor constraints, and setting the targetv, airresist and drag attributes on the proxy geo in order to get a physically plausible result.
Switching the context to DOPs outside of that isn't helpful in any way since those attributes are only useful in the context of a bullet RBD simulation as well as it relying on the car's position being updated by an external process - the RBD Solver.
When this is enabled, it only snaps the car in position at the first frame of the sim (or whenever the car appears in the sim), and from there the car's current position, advected by the sim, is used to calculate where it wants to be and how it should get there by adjusting attributes on the steering conetwist constraints and the hard motor constraints, and setting the targetv, airresist and drag attributes on the proxy geo in order to get a physically plausible result.
Switching the context to DOPs outside of that isn't helpful in any way since those attributes are only useful in the context of a bullet RBD simulation as well as it relying on the car's position being updated by an external process - the RBD Solver.