Dear all,

I am currently working on a project for a major client that involves animating a multi-axis robot arm (see attached image) - the arm comprises several rigid parts with horizontal axis of rotation and a section attached to the base that has a vertical rotational axis.

I have now spent a few days hunting for information or tutorials that detail how to generate a setup to enable driving this rig from the tool-end of the arm using IK. Alas, I have had no success so far and have ended up more confused than at the start of the exercise.

As this is a time-critical project and seeming to have hit the proverbial brick wall, I am turning you all in the hope that you can advise me with either some clear step-by-step instructions or point me to some tutorial(s) on this topic.

Many thanks in advance.

Peter

here is something really rough and quick (this would make a good tutorial subject)

hope it helps

Hi Michael,

Many thanks for the quick response and for the example - very much appreciated!

A few basic questions that I hope you could address:

1. What were the key steps that you went through to rig that geometry?
   
   
2. Whenever I have tried to use bones they ended up distorting the geometry - what did you do to prevent that happening?
   
   
3. Are there any gotchas that I should be aware of?
   
   
4. In your example rig, when the chain_goal is moved around, geo1 should only rotate around the vertical axis - instead it appears to still be rotating on all axes - what would need to be done to prevent this?
   

I agree with you that a tutorial on this subject is badly needed and would be a very useful resource for those of us who are not yet Houdini experts.

Thanks in advance,
Peter

peter_i
What were the key steps that you went through to rig that geometry?

with a rig like this I try to break down each rotation individually, and rig that.
then if I see 2 or more rotations that should/could go together I try to combine them with IK or a constraint
mechanical rigs tend to be more straight forward as each piece of geometry has a definite rotation - so the rig is limited and therefore a bit easier to set up.

peter_i
Whenever I have tried to use bones they ended up distorting the geometry - what did you do to prevent that happening?

a rig like this doesn't need any deformation, so breaking up the geometry as separate objects makes things easy, and prevents unwanted distortion.

peter_i
Are there any gotchas that I should be aware of?

not really, but keep in mind that an object like this that you see in a finished animation may not be rigged to work just from the tip of that last bone - it might be rigged to require a few more steps in animation - as I've done here.

peter_i
In your example rig, when the chain_goal is moved around, geo1 should only rotate around the vertical axis - instead it appears to still be rotating on all axes - what would need to be done to prevent this?

if you change the parent of geo1 from the forward_rotation bone to the base_rotation bone then it will only move rotate in the vertical - it was just a guess form the pic


I though we had a model of something like this around, but I guess not. I'll add this to my (growing) list of tutorial ideas.

Hi Michael,

Once again, many thanks for answering all my questions so quickly.

Regards,
Peter