v10 - Knee & Foot Target bone rig

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heyvern
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v10 - Knee & Foot Target bone rig

Post by heyvern »

This is a rig using the new v10 feature Bone Targets

v10-knee-foot-target-bone-rig



The simple and standard use of this bone feature for legs (and arms) would have one target bone for the foot and IK stretching set for the thigh and shin bones.

This works quite well and is simple to set up, however it does have some limitations. One of the issues is moving the knee or joint location. With the simple set up and one target for the foot the leg can only bend in one direction. To force the leg to bend in the opposite direction, you must force a rotation key on the shin bone. This works but causes the bend to "pop" instead of smoothly animate.

Another limitation is that both the thigh and shin bones will always scale the same amount to reach the foot target. In many situations this may be good enough, but doesn't allow for "foreshortening" or independent scaling of the thigh and shin bones for front walk cycles or perspective, when the shin bone is bent from a front view it would appear shorter.

Using this rig allows for independent movement of the knee. It allows for smooth changing of the leg bend direction with no "pop". The thigh and shin bones are scaled separately based on the knee and foot target bone location.

In addition to this, I've added two extra bones above the hip bone to control either the movement of both knees or both feet. Translating the body root bone will move the entire body except the feet target bones. The feet mover bone allows independent movement of only the feet.

A top level root bone allows for the entire character to be translated.

The Anime Studio file download is for v10 only. It includes two walk cycles using the same rig. A front walk cycle and a side walk cycle.

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Some "cheats" on the rig.

To get the results needed (this would apply to any target bone rig) I used bone offset for the target bones to "lengthen" both leg bones. The original bone set up has shorter legs so they can "stretch and squash". The IK Max Stretching for a bone only "stretches" it doesn't have "squash". To compensate for this I made the bones smaller or shorter than I needed. I then offset the target bones to where they should be to start. This allows for squash and stretch.

I could have done this by simply translating the target bones on frame 1, but by using bone offset it's sort of "built in" to the rig.

Of course this will require creating any vectors "pre squashed". Not a big deal in my opinion.

EDIT:

Same thing for image based characters. The legs (or arms) images would be created normally. When imported they would be "one way scaled" on frame zero to maintain the resolution. When the target bones are offset the image is "stretched" back to "normal" size.
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heyvern
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Re: v10 - Knee & Foot Target bone rig

Post by heyvern »

Well, it looked like a good idea at the time.

Unfortunately this rig has some major problems. There is some strange rotations of the target bones that causes the "aim" bones to flip rotations "suddenly". This can cause all kinds of problems with "shapes" for limbs instead of the stroke legs I used in the sample.

In the sample file I used "strokes" for the legs and didn't notice the problem. The spinning or flipping of the shin bone had no effect on the stroke. If you use this rig with shapes and smart bones for joints the shin bone will rotate reversed unpredictably.

I still think this is a good idea. Will keep playing with it.
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heyvern
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Re: v10 - Knee & Foot Target bone rig

Post by heyvern »

OOOPS!

Okay, so it does work. The bones do flip around a bit. The problem is I applied this to another rig with smart bone joints on the leg and it "broke" the smart bones because they changed their default rotation. I had to fix the smart bones and now it seems to work. Will keep testing it though.
rocky53204
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Re: v10 - Knee & Foot Target bone rig

Post by rocky53204 »

Quite clever, follow with interest. Thanks for the courtesy of an anme file to illustrate the concept!
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ARTzuza
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Re: v10 - Knee & Foot Target bone rig

Post by ARTzuza »

Hi,
thanks for the file (.anme), it was very useful!
It would be great if in future ASP versions could implement a similar solution like currently have 3d animation softwares like Maya or 3DMax , where there is something called "Pole vector" which is an attribute of the IK solver (Target bone in AS) which can be manipulated from side to side in order to give direction to the knee (or elbow in IK arms).

Your solution is very good and in fact I'm using it in a character, but I have now the limitation of use it with smart bones :(
Last edited by ARTzuza on Wed Sep 10, 2014 2:39 pm, edited 1 time in total.
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Tutorials, Making of and more in My Youtube channel:
:arrow: :arrow: :arrow:https://www.youtube.com/c/ARTzuzaAnimation
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ARTzuza
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Re: v10 - Knee & Foot Target bone rig

Post by ARTzuza »

heyvern wrote:Well, it looked like a good idea at the time.

Unfortunately this rig has some major problems. There is some strange rotations of the target bones that causes the "aim" bones to flip rotations "suddenly". This can cause all kinds of problems with "shapes" for limbs instead of the stroke legs I used in the sample.

In the sample file I used "strokes" for the legs and didn't notice the problem. The spinning or flipping of the shin bone had no effect on the stroke. If you use this rig with shapes and smart bones for joints the shin bone will rotate reversed unpredictably.

I still think this is a good idea. Will keep playing with it.
Hey,
I have solved this problem (target flippng or spinning around) by adding another bone to control the knee target and not having to directly manipulate the knee or foot target. So, I add a new bone "ctrl_knee", and I set a contraint "bone Position control" -> "ctrl_knee", so that the position of the target is controlled by the bone "ctrl_knee". I do the same for the target of the foot, and no rotations are given defforming the smart bone.
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Tutorials, Making of and more in My Youtube channel:
:arrow: :arrow: :arrow:https://www.youtube.com/c/ARTzuzaAnimation
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negroclarito
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Re: v10 - Knee & Foot Target bone rig

Post by negroclarito »

Looks good... I'll try it. Thank you
chucky
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Re: v10 - Knee & Foot Target bone rig

Post by chucky »

Great idea Vern.Thanks for sharing it.
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strider2000
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Re: v10 - Knee & Foot Target bone rig

Post by strider2000 »

Excellent discussion. heyvern, thanks for posting the video and the rig. I learned a lot from that.

For other readers that might be interested in the topic you might also want to know about a thread
viewtopic.php?f=13&t=26456
that contains a video where Selgin shows how to get the IK to bend in the opposite direction by using the bone controls. This may be what heyvern meant by "forcing a rotation key on the shin bone" (sorry I wasn't skilled enough to follow exactly what heyvern was describing :cry: ) It also shows how to animate the knee to avoid the pop (that was helpful to me, because of the issue heyvern mentions and the fact that the controls are not quite as intuitive for me when the target bones are involved).

I see these as two alternative approachs for dealing with the same issue, both with great value. Thanks to heyvern and Selgin for the excellent tips. I'm just now starting to scratch the surface of this great program. I love Anime Studio and really appreciate this forum. Awesome!
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PaperWaspNest
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Re: v10 - Knee & Foot Target bone rig

Post by PaperWaspNest »

Does the sample file from the original post here still exist? Its a missing file right now, and I'd love to try out this solution.
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