topic Re: IK to FK switch snapping issue in Maya Animation and Rigging Forum

IK to FK switch snapping issue

tevin93 — Sun, 22 Dec 2024 06:44:44 GMT

hello

I have been working on a animation where I have the character pick up a cup from a table. In the anim I animate and interact with the cup in IK then move the hand and pick up the cup in FK.

the problem I have is that you can clearly see the switch as the arm switchs from IK to FK.

I've tried to smooth the transition and make the transition happen over 4 or five keys or putting the arm in position first then switching in the pose when it picks up the cup. but the arm breaks especially at the wrist.

Any help would be amazing thank you

https://drive.google.com/file/d/19DxfS7kblA0XYUM0Xw-A3XMFKYjLpQ2v/view?usp=sharing

(view in My Videos)

Ive attached a short video of the switch and a picture of the rig breaking

Re: IK to FK switch snapping issue

mcw0 — Sun, 22 Dec 2024 17:10:28 GMT

If you are using a blend over a number of keys, this will always be an issue. Might I suggest doing a switch at a single frame instead of a blend over a number of keys. And in your case, going from IK to FK is easy. All you have to do is at the frame of the switch, match the rotation values of your FK to the IK. No pops.

Re: IK to FK switch snapping issue

tevin93 — Mon, 23 Dec 2024 01:13:27 GMT

Yeah I've tried that to match the rotation values and switching on a single key but there is still popping in the arm and I've flattened or smoothed out the keys so that theres no hitches in the graph editor even deleting keys to make sure theres no keys stacked on top of each other but again theres still popping you can try download the folder i provided you might have better chance of figuring it out unless theres something I'm doing wrong

Re: IK to FK switch snapping issue

tevin93 — Mon, 23 Dec 2024 01:15:23 GMT

Yeah I've tried that to match the rotation values and switching on a single key but there is still popping in the arm and I've flattened or smoothed out the keys so that there no hitches in the graph editor even deleting keys to make sure there no keys stacked on top of each other but again there's still popping you can try download the folder I provided you might have better chance of figuring it out unless there's something I'm doing wrong

Re: IK to FK switch snapping issue

mcw0 — Mon, 23 Dec 2024 01:17:54 GMT

How have you implemented your IK/FK switching? Do you have separate IK and FK joint chains going through a blendColors node controlled by a switch attribute?

Re: IK to FK switch snapping issue

tevin93 — Mon, 23 Dec 2024 04:57:13 GMT

I'm sorry I didnt understand any of that. if you mean do I have a IK and FK switch in the channel box that connected to a separate control then yes Ive tried deleting keys and zeroing the attributes but I always get the pop in the forearm and Bicep....I've even deleted the keys on those on the shoulder and elbow control the key that switches from ik to fk

Re: IK to FK switch snapping issue

mcw0 — Mon, 23 Dec 2024 16:54:34 GMT

If both the IK joints and the FK joints match in rotation values, then the problem is how those values are being applied to your bind skeleton. I would select the bind joint and see what the rotation values are. Also, if you could post a screen grab with that bind joint selected, showing the channelBox, that would be helpful. Or you can graph the bind joint in the node Editor. Find how the bind joint is driven. How the rotation values are being set.

Re: IK to FK switch snapping issue

tevin93 — Mon, 23 Dec 2024 23:49:11 GMT

I'm not sure these screenshots are what you meant by the bind joint I'm not familiar with this rig or much of rigging but these are screens shots of the upper arm(shoulder joint), elbow joint and wrist joint all of which are screenshots of before and after the switch from IK to FK along with the values in the channel box it might be easier for you to see for yourself from the folder link I provided if you have maya 2023 as the rig only seem to work on that or higher...on the upper arm joint there is a difference in rotation values but when i try to make the the same it just reverts back to what it was ...sorry if this doesnt help Shoulderupperarm joint frame 55

Shoulderupperarm joint frame 56

Elbow joint frame 55

Elbow joint frame 56

wrist joint frame 55

Re: IK to FK switch snapping issue

mcw0 — Tue, 24 Dec 2024 01:01:33 GMT

In the attributeEditor for both the upperArm and the elbow, there is a connection to "offsetParentMatrix". That is where the problem is. You need to select that node and graph the inputs in the NodeEditor. See what values are present and how they are controlled.

Re: IK to FK switch snapping issue

tevin93 — Tue, 24 Dec 2024 04:21:28 GMT

I've never used the node editor or done any of what your mentioning you will have to either show me or tell me in the simplest way step by step how to do any of that. Ive takenscreen shots of the offset matrix for frame 55 and 56 for the shoulder and elbowShoulderupperarm joint frame 55

Shoulderupperarm joint frame 56

Re: IK to FK switch snapping issue

mcw0 — Tue, 24 Dec 2024 18:34:18 GMT

To do a switch you have to check on the same frame. Select the upper arm joint and switch from IK to FK at frame 55. You don't care about frame 56. At frame 55, there should be no shift in the pose when you switch from IK to FK. If there is, then there's a problem.

To track the problem, keep the upper arm joint selected and open the Node Editor. It's under the "Windows" menu on the menu bar. Click on "Windows" and in the drop down menu, about half way down, you will see "Node Editor". Click on that. Since it's most probably your first time, the upper arm joint should appear in the Node Editor window.

To it's left should be the multMatrix node, in your case, it will be named something else. But it's still a multMatrix node. And that is connected to the joint's offsetParentMatrix. If your joint is still selected, shift select the node to it's left which should be the multMatrix node, click on the number "3" on your keyboard to expand the nodes. Now you can see a detailed list of plugs. And you can see what is connected to what.

To the left of the multMatrix node, you will see its inputs. Most likely, those will be the nodes that affect your rotation. Select each of those nodes and inspect their rotation values. They should match. If not, then this is where your problem is. They need to match.

If by chance those inputs do not have rotation values, then continue tracking inputs by selecting those nodes and clicking on the icon circled in green in the above image. Continue this process until you find 2 nodes that have rotation values. I hope this makes sense. Good luck.

Re: IK to FK switch snapping issue

tevin93 — Thu, 26 Dec 2024 03:31:18 GMT

i think Ive done what you mentioned correctly. if it is correct.

the node in the white box is the upper arm joint: TheInterview_Rigging:upArm01_r_skn

the boxes in red have 0 rotation values

the boxes in yellow all have different rotation values to TheInterview_Rigging:upArm01_r_skn (node in white box)

6th node yellow frame 55

7th node yellow frame 55

8th node IK Controller yellow frame 55

Re: IK to FK switch snapping issue

mcw0 — Thu, 26 Dec 2024 08:17:24 GMT

Please select TheInterview_Rigging:upArm01Skn_r_multmat and track its inputs. You are looking for an IK and an FK node that connects as inputs to compare rotation values. And it should only be for the upArm, no hands.

Re: IK to FK switch snapping issue

tevin93 — Fri, 27 Dec 2024 05:57:40 GMT

these are the nodes I've been able to find that are linked to TheInterview_Rigging:upArm01Skn_r_multmat that seem to be associated to the upper arm

The nodes in the yellow box's offset parent matrix rotations match, but not all of their translate attributes match in the offset parent matrix. The same nodes, the two nodes in the green square's transform attributes rotation values and their offset matrix values match, both match, with one seeming to be keyed.

The nodes in the red box their attributes all match

Re: IK to FK switch snapping issue

mcw0 — Fri, 27 Dec 2024 11:58:51 GMT

Since we know TheInterview_Rigging:upArm01Skn_r_multMat is connected to the upper arm skin joint, all we want is to trace back the inputs to TheInterview_Rigging:upArm01Skn_r_multMat. In your image, it's only showing a single input. There should be at least one other input. Please select the multMat node and graph the inputs. Ideally there will be an FK and an IK connection. Trace the inputs until you find both an FK and an IK node that have rotation values that can be compared. Ideally, they will be uprArm _fk and uprArm_ik.

Re: IK to FK switch snapping issue

mcw0 — Fri, 27 Dec 2024 12:10:03 GMT

Alternatively you can try selecting the ik and fk joints directly. Copy and paste the following into the script editor window and hope we are lucky.

select -r TheInterview_Rigging:upArm_r_ik;

select -r TheInterview_Rigging:upArm_r_fk;

Re: IK to FK switch snapping issue

mcw0 — Fri, 27 Dec 2024 17:51:22 GMT

Just thought of another way to approach this. Let's see what the fkik switch is connected to. Copy and paste the following into the scriptEditor window and run it.

Then after running this code, open the NodeEditor to see what it is connected to. Hopefully it will be a blend node of some sort. Actually, there will most likely be at least a couple. One for the upper arm and another for the lower arm. And maybe a third for the hand. The upper arm blend node's inputs should be the FK and IK nodes we have been searching for.

string $attrs[] = `listAttr -ud "TheInterview_Rigging:armSettings_r_ctr"`; for($attr in $attrs) { if(`gmatch $attr "f*"`) break; } select -r `listConnections -s 1 -d 0 ("TheInterview_Rigging:armSettings_r_ctr."+$attr)`;

Re: IK to FK switch snapping issue

tevin93 — Sun, 29 Dec 2024 06:45:09 GMT

I put this script into the scene script editor and the node in the green box is the only one that showed up... I then clicked on input and output connections and there are a lot of connections but these ones that I have moved and shown here are the only ones I could see connected that related to the upper arm as well as the multimat node as well

the node called TheInterview_Rigging:upArm01_r_skn had rotation values of =rotate x: -61.059

rotate y: -69.35

rotate Z: 80.894

the nodes in red box all had a rotation value of rotate x: -12.952

rotate y: 0.000

rotate Z: 0.000

string $attrs[] = `listAttr -ud "TheInterview_Rigging:armSettings_r_ctr"`;
for($attr in $attrs)
{
    if(`gmatch $attr "f*"`)
        break;
}
select -r `listConnections -s 1 -d 0 ("TheInterview_Rigging:armSettings_r_ctr."+$attr)`;

Re: IK to FK switch snapping issue

mcw0 — Sun, 29 Dec 2024 08:11:32 GMT

Thank you for posting that image. I think we are getting somewhere. I should have thought of this before. Please select the ikHandle. The grey node in the red enclosed area. The startJoint of the ikHandle is the IK joint for the upper arm. And the corresponding FK joint control for the upper arm is "TheInterview_Rigging:uprArmFk_r_ctr". At least I hope so from the name. The IK upper arm joint's rotation will be the result of your IK hand control and the pole vector. And since you are transitioning from IK to FK, we don't need to worry about this joiint. Just note the rotation values. The FK control for the upper arm must match these values...at frame 55.

The rotation values on TheInterview_Rigging:upArm01_r_skn should be 0, 0, 0. This rig is a bit sloppy. But matching the FK upper arm control to the IK upper arm joint's rotation values should do the trick.

Re: IK to FK switch snapping issue

tevin93 — Wed, 01 Jan 2025 19:50:14 GMT

yeah this rig was created by either Lupin House or Firelight Studio for their competition that I tried to submit this anim for but I missed the deadline twice because of this issue so it became a personal project hopefully to use for my portfolio

hopefully, these screenshots help as far as observing the rotation values a lot of the nodes are connected to many different other nodes so it is quite difficult to find or track their connections and for it to be remotely organised

TheInterview_Riggingarm_r_ikhTheInterview_RiggingupArm_r_jntTheInterview_Rigging:upArm01_r_sknTheInterview_RiggingupArmFk_r_ctr