View Full Version : Toy Arm IK Rigging? (Maya 7)

05 May 2007, 06:53 PM
I'm a little lost...

I'm busy with a project for varsity and I'm a little stuck with this arm of mine. On the whole arm is four joints each doing its own thing...

Shoulder, Arm, Elbow and Wrist.

The shoulder is limited to rotate between Z but I'm not sure how to limit it so that the X rotation always stays perpendicular to the little bar.

The Arm joint is limited to rotate only in Y

Elbow is limited only to X

And the wrist is unimportant at this stage.

Now I've tried putting an IK onto this thing but it just won't do what it's logically supposed to do.

Any help (Besides moving to Maya 8.5)? I'm going to ask my lecturer tomorrow what on earth I'm doing wrong or what I'm missing.

Have a look at the scene file and you'll see what I mean.


05 May 2007, 07:12 PM
I'm assuming you're talking about the pop when you try and bring the arm up. When you have limits set the way you do that will happen, when it get's to it's limit it has to compensate to get the handle to the position you want and if that means popping in the x or z then that's what i'll do, I removed the limits on the upper arm joints and it worked for me. It's a ball joint up there anyways so i'm not sure why you wanted to limit that without seeing more of the geo. Perhaps there's a reason for the limits. Anyways, i'm using 8.5 so i'm not sure that you can open the file if I save it out. But if you can remove the limits on the upper arm and that should can limit the lower arm if you want but that's not really needed if you're using an RP and you pv constrain it.

05 May 2007, 07:20 PM
Opened up the file, at the moment there is no IK in the zip file. However, What I assume you are wanting to do is control the angle of the elbow. (IE which way it points) with an IK setup, this is achived with a pole vector. For demo purposes I generally use a NURBS circle, since I dont have to mess with lots of stuff.

Start with placing the NURBS circle at a fair bit of distance behind the shoulder. Then select the Circle then the IK Handle. Under the Animation Menu set select Constraint>Pole Vector. This will give you control over your Rotation angle that you seem to be looking for.

05 May 2007, 09:12 PM
Nope that didn't work, well it did but I obviously didn't explain myself propperly...

I've put a new picture up for a better view of the shoulder joint. It is sort of a ball joint but it's confined to one axis because of the way I made the actual shoulder...

The problem is the shoulder is popping around the arm instead of it staying in one place and the arm twists thus moving rotating the whole arm on its own axis... make sense?

Check out the shoulder and you'll see the reason for the limits

EDIT: That picture is of the shoulder without limits on it. And yes I can open 8.5

I've added some geo for you to see the twisting, between frame 12 and 13 is what is supposed to be happening but not in the space of one frame. I tried adding a Pole Vector constrain but that stops the rotation of the joint at the bicep completely.

05 May 2007, 02:19 AM
So from what I gather what you want the arm to do, is to move all around in a normal fashion but not be able to raise above a certain degree so that the geometry that you are using collides with the geometry of the peg.

Is that correct?

05 May 2007, 02:43 AM
This is what it looks like you are attempting to achieve.

If it is I can explain what i did differently. If not let me know what is not correct about it.

One of the great things about character rigging in maya is that there are several ways to accomplish the same thing. I know a number of different ways to do things, just need to know which trick to pull out of which bag.

05 May 2007, 09:16 AM
Ya thats the idea with the shoulder, the problem comes in with the joint between the shoulder and the elbow. The IK freaks out when I tell it not to bend that joint but only rotate it.

I'm not at my pc at the moment but I'll take a look when I get back. My lecturer said that I've got too many restrictions on the joints so it won't do what I wanted it to do.

So instead I'm going to fake the shoulder being "attached" to the body by putting two screw things on them like I did for the arm and then remove the joint thats between the shoulder and the elbow.

But I'll take a look at your solution when I get home.


05 May 2007, 04:38 PM
if mine is right, one of the things I would say is, that;
1. Yes you had way too many ristrictions
2. You have too many joints

The solution that I have uses no restircitions and 2 joints


The rotation for the arm in IK comes from the pole vector. The Pole Vector controls the angle for the arm. In the above example I am moving the pole vector as I move the arm. =)

05 May 2007, 08:45 PM
I had a look at your solution and thats exactly what I did to fix it... well it didn't fix it, it was just another route.

I had another idea though... (I'm not going to do it now I want to get this animation done so I can smile about it)

I could place that first shoulder bone at the pivot point of the shoulder geo (because its separate from the arm (The bit with the bicep). Then I make the shoulder geo aim constrained to the elbow joint with some limits on how it can rotate without crashing into the little ball joint effort.

It should work because the IK then only has the three joints to think about instead of four and the shoulder reacts to whatever the IK does.

But thanks anyway!

Got through it pretty nicely...

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