Reactor Chain Tutorial

[Morbid Angel]

well yes and no, bones on their own do rotate but, bones with ik cannot rotate...so...its one for the other...

[percydaman]

maybe you could write a tut. I cant open that max7 file.

[Morbid Angel]

By popular demands...da chain tutorial :P
Chain Tutorial



Ok so here is my approach to making a reactor simulated physical chain. The thinking behind it is that realistically reactor all though a great physics engine cannot simulate thousands of rigid bodies which collide with each other so another approach must be taken. Here we go:



Create your chain – the initial position must be straight for the setup then the chain can be simulated to drop and assume its natural position. Now inside the chain crate a bone structure with Spline IK enabled so that the bones are driven by the IK solver. You can enable that when choosing the bone creation method under system menu. The reason for SplineIK solver is that it is based on the spline (funny none of the max splines are called splines they are actually called shapes and spline is a maya term….makes you wonder where they took it from :P) which is essential in our setup. Another thing is that its best to know how many chain rings you are going to have. So that when the SplineIK is created you will need to specify the number of spline points to approximate the spline on. So the rule is 1 point for 1 ring. Also every bone in your bone-chain must correspond to a single ring of your chain so that on deformation it acts natural.






Now link every chain ring to the corresponding bone.






Next step is to setup reactorRope deformer. To do that we need to select the IK spline (shape) and drop a reactorRope on it.

Rope properties need to be adjusted because we don’t want our chain behaving like a rope so it has be heavy and stiff. Set the rope properties as follows:

Mass = 5 kg

Thickness = 15 – this is based on the reactor preview. I like to think that the rope should be as thick as the chain for closest approximation.

Constant – turn this on because we don’t want the chain to stretch or deform in any unusual way, and this will prevent it from happening.

Avoid self intersection – on (self collision)



For this test I will constrain a single vertex of the spline to the world so the chain doesn’t fall into the eternity.

We will need to add fix vertex (constraint to world) then under subobject select vertex and pick which vertex we will constrain.







Run the simulation.

This should work as demonstrated below.

http://www3.telus.net/public/vinnik8.../realChain.avi

Now for the twist.

The SplineIK cannot allow natural twist. So physically it is not possible with method. However there is an option on the IK solver control panel which has build in twist options. So if you really, really wanna twist it – go right ahead: Select the SplineIK solver go to motion panel and the twist options are there you can put them on the manipulated slider if you want.








Now just for fun I’m going to attach the chains to the biped character to see how it would work. First create a biped set it to the figure mode so we will attach our chains to it and it will be easier to work with. Next create 4 boxes and position them as on the picture below for the representation of the deforming mesh. Now based on the testing I did before (which are not conclusive) best animation tracking results for the physical objects and attachments work with deforming mesh. The principal is such: you need to select all vertexes in the mesh and set a keyframe on frame 0. Then the object will register the animation and sync it with reactor. In other situations it didn’t work. So the box is deforming mesh. The SplineIK is constrained with single vertex to that box. (the world constraint is removed). The deforming mesh is linked to the biped correspondent bone of the biped. Now we group the chain with the bones and IK and make a copy. Max is good that way because it preserves all the links and connections in the group. The only thing is that in every copy of the chain we need to attach a correspondent deforming mesh box to a copied chain. And then every new reactorRope needs to be added to the rope collection.






Now we also need to add to deforming mesh some parts of the biped. Such as legs and arms perhaps torso will collide with the chains so they need to be added to the deforming mesh collection.


In real character setup a proxy objects which are extracted from the character mesh will be used. In our case the biped will do. Below is a representation of the linking.






Next is to link the groups to the corresponding deforming mesh boxes using link tool. The reason for that is when the biped is switched off from its figure mode the chains must retain position in respect to the body’s position. Here is the simulation.

So hope that helps you all who struggle with chains.

http://www3.telus.net/public/vinnik8...rSim_Chain.avi

[trixian]

Nice tut. May I ask why you used the deforming mesh collection instead of a rigid body collection for the biped and the boxes? The biped parts are all rigid parts that rotate, and the boxes are completely static, so wouldn't it calculate faster as rigid bodies?

[percydaman]

excellent tut dude. Trixian, my guess would be so that you could actually skin a mesh with the biped at a later date if necessary and it would still be setup for the chains?

[trixian]

hmm...maybe, but you'd still have to unassign the biped bones and assign the skinned mesh. Not really much of an issue though.....if it works, it works.

[Morbid Angel]

next tutorial will be physical hair :P (still work in progress)

[Morbid Angel]

I must add...tried this in max 6...and man the IK is jumping all over and i cant get it to be stable...max6 is crack....so dont use it :P

[percydaman]

I must add...tried this in max 6...and man the IK is jumping all over and i cant get it to be stable...max6 is crack....so dont use it :P

now he tells me....

[Morbid Angel]

:P
percy you know when we did battlestar max 6 was crashing every second...it wasnt even funny. I cant imagine how we got thru it, but I forever then said to my self that I will not do a project in max 6 ever again. so for the upcoming one we gon go max 7 all the way. I found that reactor is way more stable, max is waaaaaaaaaay more stable. And etc. hint hint

[percydaman]

doesn't look like we are going to upgrade until max 8 comes out. Not my decision. Hopefully then we'll just go subscription. BTW, your my hero for being part of BSG. Love that show.

[Morbid Angel]

yeah me too thanks.
Here you can peak at the cylons that we did (its my demoreel all tho not finished yet)
http://funtik.com/dvinnik/Final_reel_2004.avi (need xvid codec)

[percydaman]

cool, downloading now... Hey think theres room for me at your studio? I made this awhile back during my free time. Im sure we could slap it on a ship or something... haha

[Morbid Angel]

nice tower btw
I messaged u