Rigging a spider robot

[Anonymous]

Hello all, I hope I'll be able to explain this clearly enough. I'm very basic with rigging and I'm trying to rig up this spider-like robot:

So far, what I've done is create two IK handles per leg - one an RP handle from the elbow to the wrist, the other an SC handle from the wrist to the bottom. Basically, each leg from the elbow hinge down needs to be able to move in IK, but the legs are constrained to rotate only on one axis where they connect to the main body. I achieved this by making those IK handles, parenting them to the foot controllers, then parenting the foot controllers under the main pivot controllers (the yellow curved arrows). I don't know if this was the right method, but it allowed me to get the freedom of the IK handles without getting impossible rotations at the base hinge.

Now my problem is that, when I try to attach all of these leg joints to the main body, I get the nice "spider crouch" poses I'm looking for, but the leg rotation gets messed up:

So instead of rotating correctly from the base hinge, it ignores the top half of the leg altogether and just rotates the forearm incorrectly. 

Is there a way I can fix this, or a better way for me to set up the legs?

[Anonymous]

Hey @Anonymous

Honestly the best way to be able to truly see what the issue is, is by attaching the rig file here so we can take a much better look at it! (:

____________________
Daniel López de Medrano

Remote Character Rigger
*14+ hour Rigging Course*

[Anonymous]

Here's a Drive link to the file, this site is finicky about me uploading files for some reason. https://drive.google.com/file/d/1EhJwnM73lFBX9kdBKuxGZdH4uSxOnYCG/view?usp=sharing

[dinofiguera]

 In order to have a more animator-friendly rig, I think you should be able to rotate and position a leg only by using the 

foot control.

I did a little test by only using one IK handle and two opposite aim constraints per leg.
One aim constraint is making the hip control follow the rotation of the foot control.
The second is making the foot joint, rotate around the hip control. 

Hope it is an idea that you can find helpful.

I think that @Anonymous might also have some good advice.

Cheers,

D

[Anonymous]

Thank you, Dino! So I haven't used aim constraints before. It looks like you put an IK handle from the elbow to the second-to-last joint of each leg, correct? Then from there can you briefly walk me through how to set up the constraints?

[Anonymous]

EDIT: Never mind, figured out the legs. Thank you! My only question left is how you got the body to contort correctly with the legs? I have a single "main body" joint parented under the main body controller, but without the leg joints parented to it, what setup should I use to have the legs bend along with it?

[dinofiguera · Accepted solution]

I made one image with custom names to simplify my explanation:
1. I have parented the foot ctrl to the Main ctrl (this way the foot is independent from the hip ctrl)
    and the hip ctrl to the body ctrl (this way the body ctrl will move the joints of the leg)
2. I created the iK handle from joint C to E. (I want to have only C and D to be controlled with the Ik) 
    I constrained the ik handle to the foot ctrl, now if you move the foot ctrl, only the joints E, D, C will follow.
    I parented the Ik handle to the hip ctrl. (I could leave it outside but it helps to show that the hip ctrl controls the          leg rotation.)
3. To lock the rotate plane of the ik handle, I created locator Pv, snapped it onto D and pulled up a bit,
     Then I selected it, shift selected the ik handle and created a pole vector constraint.
      I parented Pv to the hip ctrl, so that when the control rotates, the whole RotatePlane of the iK will follow.
      I dont need to move Pv anymore so I locked its attributes.
4. I want to control the rotation of E with the foot control, but I also want E to rotate around the hip ctrl 
    when I animate the foot ctrl back and forth.
    to do this, I created the locator  L. Snapped to E,  I made L control E with an orient constraint. Then I parented L to        the foot ctrl. (this way I can make L always point to the hip ctrl, and I am still free to rotate E with the foot ctrl,              because L is parented to it) .

    Now it is time to do the first aim constraint to make E always aim at the hip ctrl.
    I selected the hip control, then shif selected L and made an aim constraint only on Y, checking 
   maintain offset to be fast. (if I don´t check it, I would need to specify what local axes is pointing to what)

5.  now we can make the hip ctrl to aim at the foot ctrl so that the whole leg will rotate around it. 
     To do that, I selected the foot ctrl, shift selected the hip ctrl and created an aim constraint only on Y, 

6. if I did not forget anything, you should be able to move around the foot control, the leg will rotate to point at it
    and the foot geometry (parented to E) will aim at the hip joint to make the whole leg always oriented in the right way.
when you move your body control, the base of the leg should be free to move, by keeping the foot steady.

Hope this helps to understand.
Cheers,
Dino

[dinofiguera]

The leg joints are parented to the hip ctrl, the hip control is parented to the body control.
So the body control is controlling  the leg.  You don't need a joint for the body. The joints are only needed to deform objects or to rotate with IK handles. Beside those properties, they are pretty much like locators.

Cheers

D

[Anonymous]

Thank you again Dino for all your help. Sorry that our replies got a little bit out of timing  I did a slightly simpler setup that seems to work pretty well for me, but using your general guidelines:

I have the single IK handle set up the way you suggested, and I have the pivot controller constrained to the foot controller. Pivot controllers are now parented to the body control which has the legs moving properly. I also have one more SC IK handle from the foot to the toe, which was giving me better results as far as the toe's alignment with the leg when I raised it. I will refer back to your reply if I have any other problems!

[Anonymous]

Exactly what @dinofiguera said........ haha, his response is 100% spot on, sorry for not seeing the file attached earlier!

____________________
Daniel López de Medrano

Remote Character Rigger
*14+ hour Rigging Course*

[stephaniebellgardt]

Thanks, glad this could inspire you!