Re: Repulsion between physical and other objects

from my experience you can't trust SL2s physics engine too much, if your goal is simply to make a ferris wheel, and not to figure out how to make one relying on the phys engine to do  the hard work for you, you should use lsl to keep things right (including the position of the wheel and the seats thing (forgot the name)

this could probably be done somewhat easily  by using llMovetoTarget to keep the wheel  in place, using llRotLookAt to constantly change it's rotation, use llMoveToTarget with some trig and some other lsl specific math involving rotation to make the seats thingies move in a circle staying in the right position in relation to the current position and rotation of the wheel, and llRotLookAt to keep the seat thingies upright (this last one and the first thing I mentioned both should only need to run once, the llMoveToTarget for the wheel itself would only need to be ran again if the base has been moved or rotated)

on the parts that are colliding, see if you can make the prims phantom (it is possible to have part of a phys linkset be phantom, the trick is to make the prim flex, and the rest of the linkset phys, before linking, then link the two, with the phys part as root, and never touch the phys or flex flags), since the position and rotation would be being handled by lsl, not having to worry about the phys engine misbehaving would be better

Brandon Lockaby escreveu:

Hmm, isn't it true that when Havok4 comes under pressure, it starts simplifying shapes?  Does that not include making hollow things temporarily not hollow?  If the scenario you're banging your head against involves hollow objects then I think that's highly likely to be the cause, unless I am misunderstanding.  Sympathies and best wishes Mr. Anderson!

On Tue, Sep 2, 2008 at 11:31 AM, Kelly Linden <kelly@...> wrote:

Anderson Philbin wrote:

Hi,

 

I'm trying to build a rotating mechanism similar to a ferris wheel. llTargetOmega should do the trick but my problem is controlling the repulsion between the objects. For example, a hollow cylinder around a shaft will tear itself off the shaft if you change it to physical. The repulsion effect seems to die down at about 100-125 mm clearance.

 

I've left a hollow cylinder happily spinning about a shaft with end caps, all with 125 mm clearance. I come back an hour later and the cylinder is laying on the ground. I understand the repulsion is provided by Havok 4 when objects interpenetrate but I'm trying to find out how to measure it and, perhaps, control it. Also, there seems to be a friction effect too. My full-size object just binds, it doesn't rotate at all.

 

Is there any documentation on this? Should I be trying to independently move the components rather than using spacial contraints?

 

TIA

 

Anderson Philbin

Havok (our physics engine) uses a Collision Tolerance of 0.1m.  What this means basically is that there is a 0.1m buffer between objects.  This makes the physics calculations simpler and helps prevent interpenetrations.  But it also means physical things won't really touch.  You can see this effect clearly if you rez 1 physical cube, then rez another above it and let it drop onto the first.  After they settle you can clearly see the gap between them.

 - Kelly

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