View Full Version : simple gravity issue

10-21-2009, 03:34 AM
Hey wavers

Ive trawled through these forums and im getting no where fast-time to ask.

I need to create a simple rig where a dangling object is hinged to a moving object and needs to move a certain way under gravity (rocks along an axis). Hopefully the screengrab explains this movement.

Ie-A moves left to right and B flopps around under gravity.

How do i go about doing this...ive tried adding gravity dynamics but as soon as i try calculating im getting a "PFX for LW9 No dynamic collision item are enabled"

As you can gather dynamics really isnt my thang....sorry :stumped:

10-21-2009, 06:24 AM
If it needs to be accurate, you will need to know the mass of the parts & their centre of gravity.

Maybe you just need do a simple scale model with a ruler, cable tie & a coffee mug & either get a visual. or photograph repeatedly with a flash on an SLR camera.

Scale the model up a bit for a slower movement with a few ten litre bottles of water on a larger bit of timber & rope.

There is a volume calculator here. & it works well, but you do need perfectly joined polys, obviously http://newtek.com/forums/showthread.php?t=101458

Just dice up the Bucket into 2or 4 or more pieces top to bottom & get the volume of each section, then you will be able to get a rough centre of gravity. Steel’s specific gravity is about 7.8 times the weight of water.

Maybe someone knows of plugin that can now move the mass. Or you will need to calculate the opposing masses & their fall in relation to their horizontal path, or something like that!

10-21-2009, 07:09 AM
Just keyframe it!

10-21-2009, 07:16 AM
Just keyframe it!

Ha-yeah thats what i ended up doing. I found the old monkey hardlink tut using the polychain method. Started to give the results i was after but as soon as i threw in dynamic parenter that method went out the window.

Hey thanks Jon for the info....however an eye ball approximation would be suffice.