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DJBREIT

Real skeleton geometry

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Now that I am half way throw rigging my model with the squetch rig. I was hopping someone knows of a skeleton rig that conforms to a real human skeleton geometry. Thou I do like the squetch rig It is a lot more then I will need for my hobby project. Ever thou I would like to adapt the hand and feet gizmo’s and some of the face controls it’s a bit more then I need. The stretchability is a little more then I need. Even thou I will probably finish it as I go along for the experience. :)

 

Dose any one know of a rig with the proper offset hinges for the knees, hips and shoulders?

 

Or do I have to make one my self?

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There is a skeleton model the comes with the AM cd (eugene), this has the 2001 rig installed. You can look at the and see if that will work for you.

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Hello again

I don't think anyone understood the problem or me. My character need to sit on her heels but her thigh an calf crash into each another. Manly because how the skeletons are set up. They are missing a knee displacement bone. (See image (3)) in a real skeleton the thigh and calf bone do not meet at a point. They rotate against each other. This is what allows the knee cap to move in and out of its position making a nice rounded knee. The rigs use a pivot point to make the knee. This has the effect of pushing out the knee cap to a point an causing the thigh and calf to crash into one another after passing 90 degrees bend . If you where to move the knee bone in-between the thigh and calf it would work like a real skeletons and pull in the knee cap as it past 90 degrees and keep the thigh and calf off set from one another .This would minimize the amount of smart skin and cp weight needed to fix the problem.

The hips has another problem but I will save that for later.

If someone has the time can you test this out and see how well it works. I would but I don’t know enough about rig to get it to work.

 

fixit_knee.jpg

knee_bend.jpg

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Here is a simple demo of the problem and solution.

 

Problem: Knee comes to a point and thigh and calf squish together. Leaving a lot of work to fix.

 

bad_knee.jpg

 

Solution: Add knee bone between thigh and calf. And two more splines at angels from center knee. You then can use fan bones, cp weight and/ or smart skin to finish the job. With a lot less work. I throw this together just to demonstrate this. The knee bone should be shorter and maintain equal angels to the thigh and calf bone but it works. :)

good_knee.jpg

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DJBreit,

Great job working your way through to a solution.

Nothing revolutionary in general as every version of the wheele for joints has been

investigated by A:M users over the years,

but you've gone onto finding a solution on your own.... very unique around

these parts:)

 

Mike Fitz

www.3dartz.com

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For the knees I new the solution as soon as I saw the problem. B)

 

The hips are a little more complicated to show. It probably need to be in a rig to show the problem and the solution. I don’t know how much of an improvement it will make but as you’ve seen with the knee it can make a big different.

 

Problem in all the rigs I have seen is it only has one point of pivot. But in a real skeleton the hips have two pivot points. You can look at the skeleton that came with A:M V15 to see if you can spot the two pivot points. I will try to set something up tomorrow to show the correct set up for the hip joint.

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I always thought it was better to get the mesh to bend smoothly over a joint, not to mimick the exact mechanics

of the way a real human joint works.

I would think that the hip joint on a person has an offset pivot, rather then 2 pivot points.

Not sure how that could be?

A foot has two pivot points. right behind the toes and at the heel of the foot.

 

Looking foward to see what you come up with:)

 

Actually, the more I look at your knee, the more I like it. I think you need to make the point a bit more round as now it

looks like the space between the 1st and 2nd knuckles on a finger when bent, instead of the joint.

But you could dod that easily with smartskin or an expression on the bone.... etc

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But in a real skeleton the hips have two pivot points.

The hip joint have only one pivot. The pivot is located where the trocanter rolls inside the hip socket. There is no other articulation in the hip joint.

 

The knee is a little bit more complex. I agree. The knee acts like it have only one pivot point untill it is folded to a little more than 90°. Then the the tibia starts rolling on the back of its head. This particular movement of the knee is helped by the set of X crossing ligaments that make the knee act like flaping doors. The two bones you placed in your knee do not fold with the same angle along the whole knee movement. Also, generally, the knee pivot point in a 3D model is usually placed too far forward. And in a 2 bone arrangement, the second pivot would be placed behing the first pivot to mimick the crossing ligaments action instead of under the first. One important bone that gives the aspect of the knee as it folds is the patella.

 

You may already know the set of books by Kapandji. If not then take a look. Look at the preview pages where, fortunately, you will get some of the hips joint information. This set of book is the most detailed documentation you can find about that sort of anatomical issues. You get all kind of diagrams of the joint movements, the pivot points, the maximum angles, etc. In those books, you will find those X crossing ligament in the knee and how they articulate the knee rotation. Invaluable reference material if you want to do the exact right thing when rigging. I had those 3 books in french a long time ago and I lost them and I miss them.

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I'd be more inclined to rely on weighting the knee to get a similar effect that you have there.

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If you mean that the hip bone has two pivot points because it rests on two legs, well... yes.

 

Simulating that bit of mechanics with a hip that is really only controlled by a bone in its center is a continuing challenge to animators.

 

It would be interesting have a rig on which you could designate which leg is the supporting leg at any moment and have the hip rotate around that joint rather than its geometric center.

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I always thought it was better to get the mesh to bend smoothly over a joint, not to mimic the exact mechanics of the way a real human joint works.

 

In truth it is the opposite in most cases. If the mechanics are set up correctly it can save you a lot of time in the final adjustments and prevent many problem from coming up down the road . Its like building a house if you start with a good foundation the rest of the building goes up easy and with little problems. But if you mess up on the foundation you are constantly compensating for all those problem. That’s just the engineer in me.

 

I would think that the hip joint on a person has an offset pivot, rather then 2 pivot points.

Not sure how that could be?.

 

Partially true

It actually has the hip socked that move in three a rotational axis”X,Y,Z,” but the second axis is at the top of the main thigh bone which rotate on the Y axis from the main thigh bone. This can greatly change the geometry of the hips. Whether this translates to a better moving model or not is still to be tested. This is what allows humans to walk up right in the first place. and not walk like a lizard.

 

Actually, the more I look at your knee, the more I like it. I think you need to make the point a bit more round as now it

looks like the space between the 1st and 2nd knuckles on a finger when bent, instead of the joint.

But you could do that easily with smartskin or an expression on the bone.... etc

 

Thank’s

This situation applies to all joints “all the finger joints, toe joints and elbows. But the finger joints and toe joints do not pass 95 degrees of each other and the problem dose not show up. So smart skin or cp weight can do the final adjustments. In the case of the elbow the forearm make the elbow pointed and dose not move independently of the forearm. So it self solve the problem.

 

 

 

Also, generally, the knee pivot point in a 3D model is usually placed too far forward. And in a 2 bone arrangement, the second pivot would be placed behing the first pivot to mimick the crossing ligaments action instead of under the first.

 

The pivot point of a knee is a floating point that moves from between the thigh and calf bone “standing straight up” to in front of the knee cap when the knee is bent to its maximum position . This also works with 3D model.

 

 

You may already know the set of books by Kapandji. If not then take a look.

Thank’s

I’ve been looking for something like this when I started this.

 

I'd be more inclined to rely on weighting the knee to get a similar effect that you have there.

You can do this buy other methods the question is how much work is involved and how flexible it is.

 

 

This shows the old knee problem with the skeleton.

old_leg.jpg

 

Shows how it works with the kne spacer bone.

new_leg.jpg

see how the knee cap floats in front of the knee.

 

And with the skeleton and a skined model over each other.

new_leg2.jpg

 

A simple test model "for the knee" to see it work as you move the bones around. It only has the three bones for the leg. Use a pose window and switch to the right or left view to try it . give it a test drive.

knee_rig.mdl

 

 

I have started the hip joint test but I will need some help on adding it to the rig and making it work.hip_joint.jpg

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I always thought it was better to get the mesh to bend smoothly over a joint, not to mimic the exact mechanics of the way a real human joint works.

 

In truth it is the opposite in most cases. If the mechanics are set up correctly it can save you a lot of time in the final adjustments and prevent many problem from coming up down the road . Its like building a house if you start with a good foundation the rest of the building goes up easy and with little problems. But if you mess up on the foundation you are constantly compensating for all those problem. That’s just the engineer in me.

 

that's not what I meant.

handling the deformation of the mesh is more important, in my opinion.

If it looks right, the viewer cares not that the joint is not true to life.

 

You have great ideas going forth, but in the end, you'll most likely see what I'm talking about.

 

Mike Fitz

www.3dartz.com

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Your flexed knee is not quite right. The tibia bone should be displaced more backward. The tibia slides around the femur condyle. But the femur condyle is not a circle. It is a spiral. And when the tibia head hits the back of the femur, right above the condyle, it starts pivoting in the corner of the femur condyle and back. The femur you are using does not have the condyles modeled so it kind of misses the issue.

 

The hip joint is really only one pivot and this is where the femur head slides inside the hip cavity. The fact that the femur have an angle with its neck does not add any new degree of liberty. Adding an intermediate bone there only complexifies the rig and does not solve any issue.

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lets not quiver over details. I want to stay on topic. I will let the riggers determine if it warrants adding to there rigs. In the case of the knee it dose work and it killed two problems in one shot.

 

 

Now on to the hip.

I have add a bone “right hip joint” between the pelvis and Right thigh bone in the list.

I need to fix the right hip joint and Right thigh bone together so they act as one bone.

 

This should allow the right hip joint bone to act as the main pivot and allow the Right thigh bone to hold the geometry and swing in a more natural movement.

 

I have also added “Right Hip Orient bone as a control handle for this test. This should allow for the swing control of the hip from back to front.

 

What should I set up in the relations to get this to work?

 

After I get this to work with the skeleton I will test it on a skinned model and see if it make an improvement.

hip_bone_test_2.jpg

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Your hip setup is unnecessary, the roll handle of the bone does what you are trying to do.

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Dont take it the wrong way DJ, you're the only person in a long while to get the rigging section some needed

activity. I think you've got some good ideas going.

Keep us posted!

 

Mike Fitz

www.3dartz.com

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Don't worry I'm use to it.

 

I have been working on my character hair. But I have not given up on the hip joint.

 

Heads up on the A:M Skeleton “Eugene_2001" that came with A:M 15 is incorrectly set up. The hip ball is in the wrong spot. I thought there was something strange about it. But I’m not a medical student. :blink::o

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I'm back :)

 

I have put the hip joint project to the side and went back to the knee joints. I now have a working rig for the knee joints. The knee has not been set up to the optimize position for ether model. It was set up for demonstration purpose only. It has no fan bones added yet.

 

bone_knee1.jpgbone_knee2.jpg

 

Here is the test model.

leg_knee_bone_test_rig11.mdl

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DJBreit:

You are correct! I know what you are doing here. Also the advice the others are giving you here is correct as well. You are going for exacting radius of how bones interact in the physical world. Obviously, you have found a way to put this into a rig. New ideas are always needed for greater detail... and it is my assumption this rig would not be used for a cartoon character or anime hero... this rig is for realistic characters?

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I came to my own solution for the knee that satisfied my needs (re natural knee movement):Edit - link had no pictures so:

 

My rigging stinks BUT I think I developed a unique way to rig the knee to account for the displacement of the shin during rotation (AS THE SHIN ROTATES - THE NEW BONE MOVES IN AN ARC TO DISPLACE THE PATELLA) . See the YELLOW bone , this displaces the patella & the shin geometry is attached to this bone and NOT the shin bone.

I also created a biceps femoris 'flattener' bone (for when I bring the heel almost to the butt to compress the back of the leg. I also had the knee slider move some of the fatty/muscle tissue around the knees as the knee bends to imitate lifelike action (smartskin).

 

 

I also have to add that my knee rig was created as a pose slider to move the bones gradually...some also moved in an arc. If anyone knows of a tutorial they can point me to to say:

 

As bone "X" rotates from minimum to maximum rotation allowed/ bone "Y" moves from point A to point C/with a stop at point B at mid rotation.

 

Note: My leg splines used to be gridlike splines - straight up/straight down - positioned in/out for shape. New version has contoured splines along a natural path. From outer hip to inner knee, I think it allows for more natural musculature simulation in the model. That said I am always searching for the ‘perfect’ layout.

knee_fix_explained.jpg

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Here is a tutorial on how to add it to the existing 2001 rig. (not yet complete)

 

To add this to an existing 2001 type rig or something that uses the same leg set up. All you need to do is add three bones (per. Leg) and three relationships (no need to change any existing relationships). And it should work. I am not sure how many others thing may need to be reworked )(I’m still new at this) but CP weights and smart skin should be one of them. CP weights and smart skin would need to be reworked if your planing to bend your character knee past 90 deg. Anyway. But I think the action’s should be O.K. Will need some verification on that. “So this means use a copy”.

 

To add this. Get the length of both the Right Thigh and Right Calf bones. This will give you the total height of the leg. Also get the start point of the Right Thigh and the end point of the Right Calf.

 

Add three bones. (Per. leg) this will be for the right side.

 

We will call them Right Geom Thigh, Right Geom knee and Right Geom Calf.

 

Right Geom Thigh is child to Pelvis.

Right Geom knee is child to Right Geom Thigh.

And Right Geom Calf is child to Right Geom knee.

Set “Attached to parent on for Right Geom Calf and Right Geom knee.

Also under manipulation option set manipulation on and Translate X, Y and Z set to off for all three bones

 

Place Right Geom Thigh on the same position as Right Thigh and match the start point.

 

For the knee as of yet I don’t have any instructions as to locate the right locations for the top and bottom of the Right Geom knee. In general look at the test model to get some idea as to the length of the knee offset and position. Also keep in mine the “skeleton bones” would be spaced further apart in a real skeleton do to cartilage.

 

The Right Geom Calf ends at the end of Right Calf or the Right foot target.

 

The total length of the three new bones should equal the Right Thigh and Right Calf.

 

Repeat on the left side.

 

Change the CP’s from Right Thigh and Right Calf to Right Geom Thigh and Right Geom Calf

change the center Knee spline to Right Geom knee. Add fan knee bones as needed. No tips on that as of this posting. Make sure the handles on the three bones face to the side of your model.

 

Add Relationships. Add Target Set

Right Geom Calf Kinematic Right foot target Apply Before Action ON

Right Geom Thigh Orient Like Right Thigh Apply Before Action ON

Right Geom knee Orient Like Right Leg Hinge Apply Before Action ON

 

Note In the test rig I have added

Right Geom Calf Orient Like Right Calf Apply Before Action ON

there’s no need to add this. Also if I miss something please post.

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