Rigid Body Constraint: hinge ok, point not #40183

New Issue

Alexander N. · 2014-05-13T21:03:12+02:00

Alexander N. commented

2014-05-13 21:03:12 +02:00

System Information
Linux Ubuntu 14.x 64bit;
Windows 8.1 64bit;

Blender Version
Broken: blender 2.70a ... blender-2.70-51fa66b-win64
Worked: unknown

Short description of error
i created a "pendulum" for testing.
when i use the hinge rigid body constraint, the "pendulum" follow an expected circular path.
but when i use a point constraint, the "pendulum" leaves the expected circular path an seems to collides with something not existing.

Exact steps for others to reproduce the error

open the attached blend file
start the animation ([Alt]+[A])

the green cube follows the circular path (with the hinge constraint)
the red cube leaves the circular path and touches a invisible border and "loose much movement enegy"

bouncing, friction, damping is set to zero, so the pendulum should not getting slower, should not leave the ideal circular path and ther are no obstacle where the cube could collide with.
point_vs_hinge.blend

**System Information** Linux Ubuntu 14.x 64bit; Windows 8.1 64bit; **Blender Version** Broken: blender 2.70a ... blender-2.70-51fa66b-win64 Worked: unknown **Short description of error** i created a "pendulum" for testing. when i use the hinge rigid body constraint, the "pendulum" follow an expected circular path. but when i use a point constraint, the "pendulum" leaves the expected circular path an seems to collides with something not existing. **Exact steps for others to reproduce the error** 1. open the attached blend file 2. start the animation ([Alt]+[A]) the green cube follows the circular path (with the hinge constraint) the red cube leaves the circular path and touches a invisible border and "loose much movement enegy" bouncing, friction, damping is set to zero, so the pendulum should not getting slower, should not leave the ideal circular path and ther are no obstacle where the cube could collide with. [point_vs_hinge.blend](https://archive.blender.org/developer/F88866/point_vs_hinge.blend)

Alexander N. commented

2014-05-13 21:03:12 +02:00

Changed status to: 'Open'

Alexander N. commented

2014-05-13 21:03:12 +02:00

Added subscriber: @beta-tester

Lukas Tönne commented

2014-05-14 11:30:26 +02:00

Added subscriber: @LukasTonne

Lukas Tönne commented

2014-05-14 11:30:26 +02:00

Can confirm this looks bad.

Increasing the Steps Per Second in rigid body world settings helps a bit, but still shows quite blatant error.

Same result happens with "Generic" (6dof) constraints on (0,0,0) translation limits btw. IMO these constraints should be much more stable in simple cases like this, so looks like a genuine bug to me.

Can confirm this looks bad. Increasing the `Steps Per Second` in rigid body world settings helps a bit, but still shows quite blatant error. Same result happens with "Generic" (6dof) constraints on (0,0,0) translation limits btw. IMO these constraints should be much more stable in simple cases like this, so looks like a genuine bug to me.

Lukas Tönne commented

2014-05-14 13:43:50 +02:00

So, apparently the distance between the two bodies is the crucial factor here. When you move them closer together it becomes very stable, moving them further apart causes ridiculous inaccuracies that build up over time. The "collision" you observed is probably some sanity limit based on a bounding box or so.

Lukas Tönne commented

2014-05-15 13:10:26 +02:00

Changed status from 'Open' to: 'Archived'

Lukas Tönne closed this issue

2014-05-15 13:10:26 +02:00

Lukas Tönne self-assigned this 2014-05-15 13:10:26 +02:00

Lukas Tönne commented

2014-05-15 13:10:26 +02:00

I'm closing this, because i think this is not a bug. Constraints are dynamic features and they can be quite susceptible to large/small values (distance, mass etc.).

The only viable generic solution is to really crank up the iterations (steps per second), unless you can build the scene in a more appropriate scale (ration of gravity to distance is what matter most here).

I'm closing this, because i think this is not a bug. Constraints are dynamic features and they can be quite susceptible to large/small values (distance, mass etc.). The only viable generic solution is to really crank up the iterations (steps per second), unless you can build the scene in a more appropriate scale (ration of gravity to distance is what matter most here).

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Rigid Body Constraint: hinge ok, point not #40183