Hey everybody.

I try to simulate a large falling rock, that is being shattered in to many small parts as it hits the ground (pretty simple).

I have divides the rock in many small parts and made them all to Dynamic Rigid Bodys.
When I simulate, the big rock seems to fall apart just the way flying down.

How can I tell the small pieces of rock to stay together as the original geometry until the rock hits the floor?

This might be a pretty easy case, but I am new to dynamic animations and there are not so many tutorials on MassFX yet.

Thank you in advance!

Hi,

I’m a Maya user so my terminology might be a little different than 3DS but I’ll try to use generic terms.

First, you need two different sets of models. 1) your rock in its unbroken original state. and 2) your rock broken into pieces.

Now, take the unbroken rock and set up the simulation so it falls and hits the ground. Cache the simulation. Now, at the frame right before the rock hits the floor get its dynamic info, that is, its velocity and such, and take note of it some where.

Now, take the shards, place them exactly where your whole rock is now before its about to hit the floor. Set the initial dynamic properties for the shards to those that I said note of before. And run and cache the simulation from that frame.

Finally, you just have to key frame the visibility of the rocks. First, have the whole rock visible from the beginning of the animation until right before it hits the ground. Then, have the rock shards not visible until the frame that you make the whole rock invisible.

That would be the most direct and manageable method to getting this effect.

Okay, I just imagined a solution like this.

So to transfer the velocity of the original object to the fragmented object’s initial velocity I have to use MaxScript, I guess?

I don’t know how MassFX works, but in older Max versions, reactor would get the initial velocity from keyframes you set for your object before the simulation starts. So if your sim starts at frame 10, you would keyframe animate your objects falling down from frame 5-10 or something.

3ds Max 2009 SP1, 2010 SP1
Maya 2012
Windows 7 Professional 64-bit
Dual Intel Xeon E5520, 6 GB Ram
NVIDIA GeForce GTX 460 OC

If you go that route then the objects need to be defined as Kinematic and set the Until Frame appropriately.
There are also options within the MassFX Modifier to set an Initial Velocity (which I’ve not tried) on the Advanced rollout.

Max 4.2 through 2014, Composite 2014.
XP-64 (SP2).
nVidia 9800GTX+ (512MB) (Driver 314.22).
i5-3570K @ 4.4GHz, 8Gb Ram, DX9.0c.