turning physics on and off

[Fergus]

I'm sure I must be missing something...

Is it possible to turn physics on and off during an animation?

[Tagirijus]

You can "bake" the physics. Go in the group-panel for "physics". If you turn on "Use baked physics", the physics won't be calculated any more, while the option is checked on.

I hope I could help you; good luck!

[Fergus]

OK

Thanks

That made sense.

Steps seem to be...
1. set up the physics group and its layers
2. run the animation once
3. go into properties for physics group and in physics tab check "use baked physics"
4. in sequencer, move the physics group to the point you want it to begin

this has worked in a simple test
is that what you were suggesting?

at a more complex level, I am wanting to get an animation to set off the physics, but I can see a few options which I must try out......

[Fergus]

think I've got it...

tried the above and then added a simple head-butting character on a totally separate layer, timed to strike a mighty blow just as the physics begins its sequence

http://www.youtube.com/watch?v=sr5hv5oLODk
or (a little bit more on the screen!)
http://www.youtube.com/watch?v=TvmStJDNhK8

[Fergus]

now for a further thing...

I want to have physics group active and then at some point remove a prop which is holding something up and by this action let that thing fall. (eg a bucket of bricks)

Since the prop has to be part of the initial physics in order to hold the object up against gravity, I am confused as to how to move it midway through the physics/animation. This is not something I can do by baking, I feel. Any thoughts?

[heyvern]

set all the objects to "Start asleep". Then on the frame you want to move the object to start the physics use the menu item:
"Animation/Nudge Physics Object..."

Set a value and direction. This will cause that object to be moved and start the simulation.

-vern

[Fergus]

thanks Verne

that helped a lot

now another question, if I may...

after I got the prop out of the way I modified the "floor" only to find the ball object I have released does not interact with the newly modified floor (see video link below)

The floor is checked as a non-moving object within the physics group.

Any clues? I'm guessing physics objects cannot be changed without effectively removing them from the physics.

http://www.youtube.com/watch?v=Sbw5WIYEF3Y

[sbtamu]

thanks Verne

that helped a lot

now another question, if I may...

after I got the prop out of the way I modified the "floor" only to find the ball object I have released does not interact with the newly modified floor (see video link below)

The floor is checked as a non-moving object within the physics group.

Any clues? I'm guessing physics objects cannot be changed without effectively removing them from the physics.

http://www.youtube.com/watch?v=Sbw5WIYEF3Y

Is the force field checked?

[heyvern]

You can't animate the points of a physics object. The physics is based on frame 0.

To create that same effect just duplicate that layer. One for the physics and one for the animated point motion. For the physics version duplicate layer, copy the last point motion key frame to frame 0, delete the other point motion keys, and turn off visibility. Key visibility on at the spot you want the physics to start. For the layer version showing the animated points, turn off visibility at the same spot as the other one turns on.

This will only create a physics effect if nothing is interacting DURING the point animation. Physics can't detect the point motion changes over time. The above suggested solution would only work as long as the rolling ball doesn't interact with the non moving layer until it has stopped point motion animation.

-vern

[sbtamu]

You can't animate the points of a physics object. The physics is based on frame 0.

To create that same effect just duplicate that layer. One for the physics and one for the animated point motion. For the physics version duplicate layer, copy the last point motion key frame to frame 0, delete the other point motion keys, and turn off visibility. Key visibility on at the spot you want the physics to start. For the layer version showing the animated points, turn off visibility at the same spot as the other one turns on.

This will only create a physics effect if nothing is interacting DURING the point animation. Physics can't detect the point motion changes over time. The above suggested solution would only work as long as the rolling ball doesn't interact with the non moving layer until it has stopped point motion animation.

-vern

I forgot about physics not using animated points. I found that out while messing around with physics when 1st released.

As for the force field, Ive noticed if the ball has force field checked it will pass through the non moving object also.

[Fergus]

OK

thanks for help to date

here's the result of following Vern's advice on duplicating the floor and using visibility

http://www.youtube.com/watch?v=ULHgmjgEXdM

2 reflections:
i) the insight that counted for me was that physics is done on frame0 shapes - everything else flows from that observation

ii) I noticed that I had to have the reshaped floor obscure the original floor entirely, otherwise the ball rolled "across" the frame 0 shape - ie it was up in the air. But I now think that's because I had the animating floor in the physics group - I presume I get greater flexibility by keeping it out of that group; after all, it really has no part in the physics, it's just a visual thing - the physics takes place only on the "final shape"

so, thanks for the tips and help, I'll keep learning

[sbtamu]

The physics is really fun to play with, ATM I'm trying to make a basketball bounce off a lot of stuff and end up going in the basket.