CGTalk - Simple bones/IK rig? (newbie help)

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TheCaptn

06-11-2003, 04:43 PM

I have a pretty simple mechanical structure that I want to animate with IK, but I can't even get the bones set up.
I've never tried anything with bones before, hell I rarely animate anything at all. I've read up on the principals, the differences between FK and IK, and the various solvers (HI seems to be what I want, right)?
But it's all academic, and I'm struggling with the simplist technical things.

The few tutorials I can find seem to ignore the fact that when you create bones they're locked or something, and can't be moved into their correct positions.

Here's what I've got:
http://wolf.alphalink.com.au/maxhelp_bones01.jpg

I drew the bones in the front view since that has the most visible 'limbs'... But they're still only drawn in by hand and all of them need to be shifted slightly into their correct pivot spots. The last one needs to be rotated 90 degrees to match the last arm too.
But I can barely move them. Some seem to move slightly and others not at all.
I haven't applied any bones to the objects yet.

Speaking of which, once I have the bones in the right spot, does it matter that the limbs are still seperate objects? They don't even touch each other since I just want them to rotate on their single-axis pivot points.
(You following me still?)
I figured it would make it easier to apply each object to its bone if I kept them seperate. If I attach them together it'd mean a lot of fiddly vertex picking.
Now that I think of it, I'll need to scale the bones so they fit -inside- the mesh objects right? Or won't that matter, since the mesh won't deform, just pivot?

Once I've got that all worked out limiting the movement to a single axis for each limb should be easy right? It's just a matter of keying in the desired rotational values?

polygun

06-11-2003, 06:21 PM

Im not exactly a rocket scientist when it comes to setting up rigs, but im pretty sure that it is possible to attach bones to seperate objects even though the bones are in a single chain.

If you apply the skin modifier to each of the parts and add the respective bone, you should be fine. Be sure to edit the envelopes so the influence on the mesh is proper.

But like I said, Im no genious. This is how I would approach it though.

TheCaptn

06-11-2003, 08:09 PM

I need to get the bones to move to the right spots before I can do any of that though...

But when you talk about editing the envelope that basically means the area of the mesh influenced by the bone right? Doesn't that just happen when I apply the object mesh to the bone (since I have a single whole object for each bone)?

CapnPanic

06-11-2003, 10:30 PM

okay to position bones, go to the hierarchy panel on the right and poke the 'don't affect children' button, this should allow you to move/resize bones without their constraints getting in the way :)

next poke the 'ol f1 button and search through the max help for 'bones', as this should bring up a ton of info on setup for ya :)

xynaria

06-12-2003, 04:30 AM

Any chance of telling us what you are trying to do with this because at a casual glance, this kind of set up doesn't really look like it would be solved by bones at all. The other thing to note is that bones are parametric in their width settings so you can alter their volune that way. :)

TheCaptn

06-12-2003, 04:53 AM

Thanks.
I found where the 'Don't Affect Children' bit is in the help file after you mentioned it... I've read straight over the top of it a couple of times... Go figure.

I've got it mostly worked out now... All the bones are in place, envelopes arranged, the IK chain works, and I've got them rotating on their pivot points on a single axis.
I haven't limited the angles of rotation yet but I should be ok with that now too.

I do have one more question though. I had a look through the help (RTFM and all that) but I'm not even sure what to search for in this case, so that limits my effectiveness.
At the moment the joints all rotate on the global axis, which is a problem because if one arm pivots 90 degrees one way that should be changing the axis that its children rotate on... i.e. from the X axis to the Y axis.
But at the moment the children still rotate on the X axis, which disconnects that arm from its parent.

I figure I should be doing something different where I set the axis rotation, maybe that 'Axis Order' rollout?
I can't make much sense of the help on that though.

TheCaptn

06-12-2003, 05:05 AM

Originally posted by xynaria
Any chance of telling us what you are trying to do with this because at a casual glance, this kind of set up doesn't really look like it would be solved by bones at all. The other thing to note is that bones are parametric in their width settings so you can alter their volune that way. :)

lol... I whipped up the model especially so I could play with IK a bit. It's not actually a project, just a 'practice dummy'. :arteest:
All the tuts I've found deal with organic skeletal animation, walking, arm movements, that kind of stuff. I'm more interested in mechanical swing arms and things like that though, so that's what I'm practicing.

I seem to recall seeing a Backhoe tut that dealt with some of this, but I can't find it anymore.

And yeah, I'd already found the width settings for the bones and changed them so that the bones fit neatly into the model.

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