View Full Version : Mulching Grass - Ideas?

04-22-2005, 06:44 PM
I am stumped for the moment.

I am trying to animate a string rotary trimmer cutting some tall grass and then it gets mulched into bits as the tops fall back down into the blade.

I decided to go with a LW dynamics approach after considering some other options, but I'm not locked into this way of doing it if someone has another idea.

I can't seem to get the desired result of cut first mulch second. Here is the setup

I have a trimmer collision object - just a bunch of low poly blades spinning that are dissolved out. The grass is made of 1 object with 10 layers. The first layer is the lower portion of the grass and the rest of the layers 2-10 are individual blades that get cut off.

On the top grass objects I have HardFX with
Piece Mode set to 1Piece>Parts(Collision)
Under the Collisions tabe I have Start by Collision checked on
and some gravity applied

When the blade hits a piece of grass it gets cut off
but as it falls down through the path of the blade it isn't getting mulched up like I had hoped. When it hits a ground collision object it crumbles into pieces (polys) but it just doesn't look very good.

Anyone want to throw out some suggestions on this? I appreciate it very much!

04-22-2005, 07:04 PM
Just a thought;
your pieces are falling between the blades on cutter I would think by your explanation. sooooo...
If you have section 1 effected by blades and they cut ok, then I would have sections 2 thru last one effected by a fake ground plane thats dissolved out and is on the same plane as your cutters.
That way when grass falls back, instead of depending on blades to fracture them, they hit the gound plane by the blades(Which is a full solid disk) they then fall apart and either go shooting off (like the blade actually hit them) or just fall to ground (probably a percentage of each would look good).

04-22-2005, 08:13 PM
Great suggestion, First, the dissolved blade I am using for collision is actually like 60 blades to increase the probability of hitting. As for the ground plane I tried something like that and it was great but had some problems too.

It does break all the cut grass blades into perfect pieces when they pass through the imaginary plane that the blade is on, but since it's a plane they get stuck there and never fall to the "real" ground plane. I tried experimenting with a poly checkerboard with every other poly missing, but the results were not good at all.

Thanks very much for the idea.