The scene->Rigid Body World->Speed =1.0 to the value of 2.1 #97089
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Reference: blender/blender#97089
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System Information
Blender 3.1
Operating system:
ubuntu20.04LTS
Graphics card:
Blender Version 3.1
Calculation of position and velocities of the rigid body is changed when the value of scene->Rigid Body World->Speed =1.0 to the value of 2.1 is changed.
Short description of error
I want to simulate a parabolic movement, in this there are two balls one ball has atached a path calculated using drivers, and the other ball is moved by a one cilinder that has a velocity of 20m/s when the ball is at the end of the cylinder, and the velocity that I has the issue is located in scene->Rigid Body World->Speed =1.0 velocity from 1.0 to 2.1
Exact steps for others to reproduce the error
Open the file located here : https://gitlab.com/Internetza/blenderanimationsscriptphysicsrender/-/blob/master/movimientop2.blend
set play
change the value scene->Rigid Body World->Speed =1.0 to 2.1
Based on the default startup or an attached .blend file (as simple as possible).movimientop2{F12976755}
Added subscriber: @Netza
Added subscriber: @OmarEmaraDev
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
The documentation says:
But the Speed does make the animation totally different, which I guess contracts or expands the time leaving the space as is. Tagging the module for more information.
Added subscribers: @ZedDB, @LukasTonne, @sreich, @lichtwerk
Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'
I will confirm for now since I also think this is not working as expected.
You can somewhat try to work around / compensate by adjusting the solver iterations, but that only works to a limited extend.
Most of the time I had contact with the Rigid body World Speed, it was not working right.
The outcome of the simulation (in this example the trajectory of the ball) should not be affected by speed like shown in this example
Note there seems to be a fundamental flaw with this setting as outlined in #38391 (Animating the speed setting in Rigid Body World causes strange behavior with constraints)
That particular report was closed, but this was also animating the
Speed
, so prefer if @ZedDB, @LukasTonne or @sreich could comment here (or classify accordingly -- this might very well be a Known Issue that is not going to get fixed anytime soon)I'm not sure I understand what the issue is?
If it's the fact that the arc of the ball gets smaller as the speed gets larger, then it's expected behaviour.
If you increase the speed of the simulation, then from the perspective of the simulation animated object will appear to move slower and therefore the forces they exert will be smaller.
Hello Sergej Reich (sergof) , if you can see the velocity do not make the correct calculus. using the default scene->Rigid Body World->Speed =1.0, and when it is changed to 2.1 it make an aproximated correct calculus. thats is the issue. then Why it does not make a correct calculus with the default value 1.0 and why it make an aproximated correct calculus with 2.1?
Ah, if it's about the accuracy of the physics involved then there are several things here:
Maybe I'm missing something, but as far as I can tell the setup accelerates the ball to something closer to 40m/s rather than 20m/s when speed is set to 1.0.
Giving the ball an initial velocity by colliding it with another object is has many problems. Collision handling is the most complicated part of the simulation and every setting will have an effect here like the collision shapes used, the number of simulation steps and constraint solver iterations as well as things like the contact points between the objects. Even if the initial conditions were perfect, the nature of the simulation methods used here makes it almost impossible to control this sort of thing precisely.
Pardon then, I always got it wrong. I was under the impression that the intend was to use this for slomo effects and such [which break in these situations]
Added subscriber: @dfelinto
Thanks for the report. Marking this as known issue since it depends on the rigid body system which at the moment has no active developer. I'm tagging Sergej here anyways in case he wants to tackle any of those. Anyone wlse interested on that can also join the geometry nodes meetings to get onboarded.
Rather than a known issue, I'd say there is no issue here and things work as expected. Unless I'm missing something.
Changed status from 'Confirmed' to: 'Archived'
Thanks Sergej, it is your call here. Closing this as archived then. Feel free to change any of the other known issues as bugs if you think you may tackle them (or to close if they are working as expected).