Q&A: “How can I use IK and bones to rig a chained weapon?”
Chris Darling’s after an epic flail; Glen Southern’s here with some Cinema 4D help
Find the supporting files for this Cinema 4D Q&A here.
There are always several ways to do a particular task in Cinema 4D. To make a dynamic chain you can use rigid body, hair splines, cloning and even an IK chain. It all depends on how you want the model to behave in the scene and how you want it to react with other objects. For this project you just want to be able to animate the shaft of the flail and have the chain and spiked ball follow it and react as they would in real life. This method is great for a flail that a character would carry around, allowing some nice dynamic animation on the links.
To model the shaft, create a basic cylinder and rotate it 90 degrees so it’s horizontal in the scene. Scale it correctly and then duplicate it. Scale up the new copy and use fillet to round off the edges at the back and front. This becomes the metal part at the bottom of the flail. Duplicate that and move the new object forward along the shaft, and that becomes the front part that will be attached to the first link.
To model the link, make a rectangle spline and round the corners. Add a circle spline and drop the two of them into a loft NURB, giving you a chain link shape. Scale it and then duplicate it. Rotate the duplicate link and position it halfway into the metal end of the shaft.
Select the first link and duplicate it again. Rotate that one 90 degrees around Y and move it down. Select the two links and duplicate those a few times, and then line all the links vertically. To make the spiked ball, use a basic sphere and a cube. Select one face of the cube and shrink it down to make a pointed spike. Duplicate this a few times and position it around the ball. Using connect and delete, make these into a single object. For this project I made the spiked ball quite small (not much larger than the chain links). If you increase the size too much you’ll have a hard time making the chain movement look realistic with this method. I chose a basic material to give the look of old metal and a wooden material for the handle.
Click to select the first link after the shaft. Right-click and add an IK tag from the Character menu. You’ll see an end goal dialog box. Drag and drop the Spiked Ball object into the end goal box. Change the IK solver to 3D from 2D and make sure Enable is checked in the Dynamics tab. If you select the shaft at this point the chain will move in a natural way.
If you select the handle model and move it left and right, the chain and ball will move accordingly. However it may look as though the chains are made of lightweight material and not a heavy metal. One way to improve how this looks and reacts is to increase the drag slider to 50-60 per cent. Try moving it again: it will now react in a much more realistic way.
This method is one of only a few ways to create this sort of chain weapon and it has one main disadvantage: the spiked ball and chain need to be able to react with other objects and items in the scene. For that you need to be a little more adventurous and enter the world of joints or even the MoGraph Cloner.
Create a link
Make the link
Create a rectangle spline and click Rounding. Adjust the size parameters, then create an N-sided spline and set it to 8.
Use a Sweep NURBS
Drop in a Sweep NURBS tag. Select the N-sided and the rectangle NURBS and drop them into the tag, then adjust the settings.
Use the link in your models
This link can be used with the Cloner Tool, added to spline dynamics and even used with the Tracer Object.
Glen Southern is a freelance 3D artist with over 15 years’ industry experience in film, TV and games, and the owner of SouthernGFX
on Monday, August 13th, 2012 at 3:42 pm under Guides, Technique, Tutorials.
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Tags: Cinema 4D, nurbs