IK issues

pandorian

Member
I've constructed a model in Modeler and have created the bones for it in Layout (only the spine and left side). The bones that I've created thus far include rotation limitations for the left arm and most of its joints (including elbow, wrist and fingers) as well as the left leg (including knee, foot and toes). I've also renamed all the bones with the string LT attached where necessary. I've mirrored the left arm and it's hierarchy (starting at the left shoulder) as well as the left leg and it's hierarchy (starting at the left hip). Everything was successful, the right side of the arm and leg mirrored the rotation limits as well as adopted the RT string attached to the names of the appropriate bones. I physically tested the movement of both arms and legs from the left and right side, and they both move as they should.

The problem seems to be occurring after I add IK to the legs. When I add IK to the LT leg it works beautifully. however, when I add it to the RT leg, upon testing it, it deforms with unexpected and unwanted results. The LT side continues to work fine with the IK, just the RT leg seems to be the problem.

I've considered recreating the bones of the RT leg manually, (as opposed to having it mirrored) but figured I'd reach out here before doing so as I'd like to learn and understand WHY this is happening only to the RT side and not the LT. I've attached images to further illustrate what I'm talking about.
 

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  • LEFT IK good.png
    LEFT IK good.png
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  • RIGHT IK bad.png
    RIGHT IK bad.png
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  • RT bad LT good.png
    RT bad LT good.png
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pandorian

Member
I decided to re-create the RT side of the leg (starting from the hip bone down) while awaiting a response and found that for whatever reason, the goal I created for the RT side refuses to attach to the foot bone despite following the same instructions for the LT side goal . (the LT side goal is attached to the LT foot and is still working properly despite the RT side issues) The RT side goal moves on its own without involving bone movement. I made sure IK is enabled and while the LT side continues to function as it should, the RT side goal does not. If I turn bones ON the mesh suddenly distorts (more on the RT side than LT) but the bones stay intact, with the LT side goal still functioning but RT side goal not functioning as it should. When I turn bones OFF, the model and bones and mesh fall back into their correct position. While the bones are OFF, I can successfully rotate the leg joints (thigh, knee, foot, toes) of BOTH LT and RT sides without issue (though it is not moving the mesh).

The further I try to figure this out, the more problems I seem to encounter. I'm completely out of ideas of how to fix this and hope someone can help me figure out what I'm doing wrong.
 
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pandorian

Member
This is the result of attempting to Mirror the LT side of the leg
 

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  • Screen Shot 2020-07-31 at 10.51.07 AM.png
    Screen Shot 2020-07-31 at 10.51.07 AM.png
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shrox

Man of many cells.
I've constructed a model in Modeler and have created the bones for it in Layout (only the spine and left side). The bones that I've created thus far include rotation limitations for the left arm and most of its joints (including elbow, wrist and fingers) as well as the left leg (including knee, foot and toes). I've also renamed all the bones with the string LT attached where necessary. I've mirrored the left arm and it's hierarchy (starting at the left shoulder) as well as the left leg and it's hierarchy (starting at the left hip). Everything was successful, the right side of the arm and leg mirrored the rotation limits as well as adopted the RT string attached to the names of the appropriate bones. I physically tested the movement of both arms and legs from the left and right side, and they both move as they should.

The problem seems to be occurring after I add IK to the legs. When I add IK to the LT leg it works beautifully. however, when I add it to the RT leg, upon testing it, it deforms with unexpected and unwanted results. The LT side continues to work fine with the IK, just the RT leg seems to be the problem.

I've considered recreating the bones of the RT leg manually, (as opposed to having it mirrored) but figured I'd reach out here before doing so as I'd like to learn and understand WHY this is happening only to the RT side and not the LT. I've attached images to further illustrate what I'm talking about.

Try using skelegons in modeller to layout the bones, it's much easier. There is less tweaking them later too.
 

jwiede

Electron wrangler
This is the result of attempting to Mirror the LT side of the leg

Are you certain the right leg's IK is pointing at its own goal, as opposed to pointing at the left leg's IK goal? It kind of looks like it's pointing at the left leg's goal.
 

pandorian

Member
Are you certain the right leg's IK is pointing at its own goal, as opposed to pointing at the left leg's IK goal? It kind of looks like it's pointing at the left leg's goal.

Yeah, I've gone over the process quite a number of times, that being one of the first things I checked for .... I've even gone so far as to Mirror the working LT Hip hierarchy with working IK and goal... same result
 

shrox

Man of many cells.
Yeah, I've gone over the process quite a number of times, that being one of the first things I checked for .... I've even gone so far as to Mirror the working LT Hip hierarchy with working IK and goal... same result

I missed that. Maybe something as simple as saving, closing layout then reopening might fix it.
 

pandorian

Member
Try using skelegons in modeller to layout the bones, it's much easier. There is less tweaking them later too.


I thought I saw footprints on this path ... yeah, that was my next option. I've done basic rigging with Skelegons and wanted to give Layout's version a try, always nice to have options. I'll rig it in Modeler but would still like to understand where the problem lies when I attempt it in Layout.
 

pandorian

Member
I missed that. Maybe something as simple as saving, closing layout then reopening might fix it.


Yep, done that a few times to no avail. I'm currently running the 2020 version of LW, I gave it a try on one of my earlier versions and had the same result.
 
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Kryslin

Well-known member
Ok, I think I can see what is going on. It looks like your bank angle is off on the right leg.

In order to work reliably, Lightwave IK has to function on a plane. This is usually a bone that targets the goal, and whose bank angle is controlled by a pole item. The rest of the leg is parented to that.

RH can explain it better than I can...
FK/IK Basics - https://www.youtube.com/watch?v=gd1ds0gKnYU&list=PLTds3QePYrWEWipwKkLmyNT4Tf_JTigM2&index=8&t=0s
Inverse Kinematics - https://www.youtube.com/watch?v=T2VYPnVIW0Y&list=PLTds3QePYrWEWipwKkLmyNT4Tf_JTigM2&index=16&t=0s
 

Shabazzy

LightWave Fan Boi
Well, from the little information available I can see there are a few problems with the rig (which leads me to believe there could be more that would be revealed if we had the scene file and object).

The first thing I notice is that you have a joint (i.e. two bones) in both thighs which is a potential point of weakness for animating. The thigh should only really have one bone in a human character but I think I understand why you have two.

The higher of the two bones would usually act as a hip joint bone and would be very small in size and protrude toward the positive (or negative) z axis with both ends of the bone in line with each other when looking at it in the back/front viewport.

Once done the next bone in the chain would become the thigh bone and the head of the thigh bone (the short pyramid looking end of the bone) would then be attached to the tail of the hip joint bone.

The tail of the thigh bone would then be attached to the head of the shin bone and the tail of the shin bone to the head of the ankle bone.

So that would be the correct bone chain.

The reason for a hip joint bone is to do with having better animation control of the character when it comes to rotation of the bones (technically you don't really need to have the hip bone). Having a hip joint bone rotated in the direction described above allows us to have better control of the pitch direction of the thigh bone which is fundamentally important to having bones animate the way you expect. The same is true for the shoulder and wrist.

Once I'd corrected both legs, the next thing I'd look at is setting up the IK chain.

Each respective hip joint bones are to be used as the "post" of the IK chain by selecting each one in turn and going into motion options>IK and Modifiers and activating Unaffected by IK of Decendants. That way we know that each leg's IK chain will be rooted with these bones. The IK chain does not go any further up the body than this.

The ankle bones will be the "Puller" bones in the IK chain. The bones that you will "pull around" with the Goal controllers that also "pull around" all the other bones in the IK chain. The IK chain does not go any further down the leg than this.

Moving down to the thigh bones and while in the motions options>Controllers and Limits>Rotation settings I'd have each thigh's Heading and the Pitch controllers set to Inverse Kinematics and leaving the other settings at their defaults.

Moving down to the shin bone which will act a knee joint and entering motions options>Controllers and Limits>Rotation settings I'd have each shin's Pitch controller set to Inverse Kinematics and leaving the other settings at their defaults.

Moving on to the goal objects, (assuming they're not already created) I'd add a couple of nulls and name them "Rt_foot_Goal" and "Lft_foot_Goal" then click on the Edit button. In the menu I'd change shape to Pyramid (or you can choose any shape you like) set the scale to something more proportionate in size to the ankle bone and set the Label to "Right (or Left) Foot Goal" and click OK.

I'd position them at the tip of the head of each ankle bone and then select the ankle bones and go into motion options>IK and Modifiers and change the Goal object to "Rt_foot_Goal" and "Lft_foot_Goal" respectively and activate "Full-time IK", leaving everything else at their defaults.

Now assuming that your bones were created correctly, and Setup>Enable IK (Shift + F8) is activated, this basic IK chain should work fine.

If you have IK set up for the "hip bones" (no I don't mean hip joint bones) you might want to deactivate them by checking the following:

motion options>IK and Modifiers - Uncheck Uneffected by IK of Decendents. Goal object = none.
motion options>Controllers and Limits>Rotation - Heading, Pitch and Bank controllers are set to Key Frames

All of the above assumes of course that your bones have been created properly and are weighted with weight maps and have their pitch axis aligned correctly.

In order to get up to speed with LightWave's fundamentals I strongly recommend that you invest in the book and DVD:

Essential LightWave v9 by Steve Warner, Kevin Philliips and Timothy Albee.
ISBN-13: 978-159822-024-7
ISBN-10: 1-59822-024-1
 
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Ma3rk

Curmudgeon in Training
Not sure which tut your following, but I recently found this site when searching for Quadruped rigging. When I asked about doing that on the forum w/ IKBooster, all I got were crickets.

http://www.learn3dsoftware.com/lightwave_rigging_menu.htm

They obviously have BiPed tuts too, but specifically had one for a Tiger which was great, but of more importance, it's the first tut I've come across where the actual use of ALL the various Bone tools are SHOWN in use, what to look for when setting bones, etc.

I even have RH's various serious & frankly he looses me a lot & have to re-re-review.

Don't know who's doing the other series, but the one I picked up is done by Adam Gibson. He's using 11.03, but it's 99.8% valid for 2019 & 2020.

All of their tut's are only $5 too, so hard to lose out.
 

daforum

da what?
Pandorian.
In 'Motion Options/ Controllers and Limits' do the bones for the "working correctly leg" have IK on any particular channels?

The "not working correctly leg" may not have the same settings...

I see Shabazzy has already suggested this.
 
Hard to tell without the scene file.
Never use limits on all the bones of e.g. the leg. This will allways give problems. Only the knee needs one.
If you use to many you limit the whole chain from being able to move in the poses you want.
Typical is that the goal object doesn't stay in the ankle region.
Also check if you don't have gimbal locks on the rotations. This will give the typical behavior you show in the images.
Put some pole vectors in for the direction of the knees/elbows. Gives you an much more stable rig.
Also when using mirror on the rig set autokey on. If you don't, the mirrored side will have different rotations and give problems ( in some versions of LW ).
Hope this helps.
 
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