Cineversity

Hi I created the same setup, but for some reason the constrain for ankle rotation makes strange twisting while rotating up and down. Also I have some priority issues. So if you rotate FootCON+ on the X axis the knee twists a little bit, and after pressing ctrl+z to undo the knee stays twisted and you need to press somewhere also to bring it back in place (because of priority issues I assume). I found that the problem is from the constraint tag in the L_ThightUpVParent, but in Bret’s leg its exactly the same, and he doesn’t have such a twist?

Hi Nikolay Kirkov,

Exploration of what I got:

Do I got the right file? It looks similar, but the set up is different and misses parts which were discussed in the tutorial.

I checked first the XPresso, and there the X-Manger, X-Group. The list here is normally relatively robust against hierarchy mix ups, but in the moment one encounters a problem, this list needs to follow the flow of information. You can click on the names or nodes, the connected part, X-Grou or Node will be highlighted, and then you can move the member of the X-Group up or down.

The Foot Twist that Bret discusses here is missing. It is more an fine-tuning option, but if he suggests it, I certainly would not skip that part, including the User Data slider.

Your scene file is also much larger than the file needed for this exercise. The parts with the Spline IK would be better discussed in line with this tutorial:
http://www.cineversity.com/vidplaytut/spline_ik
(The bendy leg… lift the foot controller while the bendy leg is 100%, it needs to be as well [lower leg] Index 0 and 1 instead of 1 and 2. There is certainly more, but not part for this tutorial thread.)
I highly recommend to focus first one time through the material at hand, and when this is savvy, to apply it to an similar case. I see it all to often, that before a scene is really working, lots of stuff is put it, but if the core of the “exercise” isn’t working - what good can it do. Reducing the scene to what is discussed helps also to stay focused, at least place other material on a Layer Browser for the time doing a tutorial, just a suggestion, as I have to do that here and it takes a lot of time to go through none related material. Thanks, I take only the same idea that the support has. https://help.maxon.net/#6197

The Leg by itself has quit some joints and I would suggest here as well, stick first to the content in the tutorial.

What works:

The most obvious to me was that the Pole was lower than in the tutorial. So I moved it up.
I set all tags [XPresso, Constrains, etc] To Camera dependent, which keeps the scene more “refreshed”.
See clip for the side movement of the knee.
https://www.amazon.com/clouddrive/share/k2bzCURd2Vr4spEVD7jmkca61tgSnU3Wqgoyld0aoN6?ref_=cd_ph_share_link_copy
Essentially the L_tight_UpV is on the corner of an triangle and it needs to be perpendicular to one corner. This is of course also based on the Parent rotation, which should be aligned as well to that “triangle”, and if that relationship is understood, things should be stable.
The Pole object is typically the third point of an triangle. This triangle is always flat, as with three points—there is naturally no other option. This flat “plane” is in return always 2D, hence the designation in the IK-Tag. On this “plane” the IK algorithm tries to solve the IK constellation. If one Joint is aligned with the pole axis, we have a problem, as for this case no 2D plane can be defined, and it twists. This was the core idea, so far I get it, in this tutorial, to keep that “plane”.
The knee on the other hand is part of the IK chain, and if the “plane” becomes different data, it changes its orientation and the knee follows. Hence my suggestion to be pretty clear and precise to have the Null object perpendicular to it. It is kind of complex, but in its core it is pretty simple and always based on the idea of a triangle. Like a three legged chair will never wiggle.
For the part of this tutorial, the Priotrity is simple, if the Object manager is set up as in Bret’s tutorial and the XPresso is organized ;o)

With focusing on the content of the tutorial, the knee works.

What you like to do with the Spline IK needs a new thread in the QA Forum. Perhaps check out Kai’s great content on it, as linked above.

All the best

P.S.: I like to share this one minute clip, with the essential core idea why the POLE is so important and why Bret discusses (from my point of view) it so detailed. His knowledge is tremendous in this area, so I hope this clip is not understood in any other way than to add a tiny little basic element in a visual way to it.

In a nutshell, a three legged stool never wiggles, and this triangle is a core key element in the IK/Pole set up. The problem discussed above is (from my point of view based on this core knowledge). IF all three “points are in one line, no triangle is given, hence the flip. OR, if the triangle changes, the “knee” in this case moves in an unwanted way.

The presented polygon is for visual purposes only and has no effect on the functionality of the IK, it just makes it visible!

https://www.amazon.com/clouddrive/share/XVdqB5KBeFlft9WGFrPyzE0yoiNjOf3BR8LRbT86Luv?ref_=cd_ph_share_link_copy

Enjoy

My question was about the twisting of the leg - If you select the Foot CON+ and rotate on the x axis the knee twists. It has nothing to do with the arms, the spine, the bendy leg etc. The problem here is in the constrain of foot rotation and the parent control that controls side -to side position on the knee pole. Rotating the foot CON+ messes the rotation of the knee, it should rotate only when we rotate the foot left and right, but in my case it twist the leg when rotating up and down. Your answer totally mashed my brain :D. So many things that were irrelevant to my question… :D

P.S. I have a slider that control the twist - both the ball and the leg twist (check the foot CON+ there are bunch of sliders).

Thanks for confirming this, Nikolay Kirkov.

So, why do you send then such a complex scene? Which I have to invest a lot of time to figure out how all of that might relate to the problem. To just ignore the context in a file is certainly not what I think is the right thing to do. So, yes, I explore it. You might be very familiar with your set up, but opening someone’s file is not the same, it takes a while to follow up all XPresso connections, all Constrain tags etc. Something might have gone wrong in the set up.

Reduce any scene to the problem, as I have even pointed to the MAXON Manual in this regard. I guess I will not make such effort in the future, and rather wait for a reduced scene then. OK? Easier for me, and you get only the answer you have seek.

I think I answered the question and the relevant question/answer was in bold. I even made a little clip to visualize the underlaying core concept.

My best advice at this point, watch Bret’s great tutorial again, perhaps make detailed notes, and be alert , e.g., when he “Zeros-Out” something and follow to the point. As you have seen, a little misalignment leads to trouble. His set up works obviously, and again, I pointed out the problem.

My best wishes for your project.

Hello,

I have followed the instructions from the tutorial and replicated the same setup, as shown in it.
I used the file from the tutorial as well.
But for some reason I don’t get the knee pole (L_Thigh.PoleCON+) going up as I translate the the foot control (L_Foot_CON+) up the Y axis.
Have I missed something important?
I am attaching the file here.

Adding to my post. I actually see that if I translate the Foot control along Y and Z axis together, then it works. But I would also expect a single Y axis translation upwards to also influence the Knee Pole. I believe some more constraints needs to be added for that to work.

Hi CaseyGregor,

If the foot is behind the the pelvis, then this up movement of the foot moves the knee downwards. I would expect exactly that.
If you move the foot a little bit forward, then the knee will move upwards as the set up for the pole, while moving only upwards.
Bret has that movement as well. It influences it in any way, but if the foot is exactly below the joint of the pelvis connection then the target/aim will not change a thing. THe foot can’t move through the body and there is a natural stop.

I can’t find a problem in your set up, only that it follows a real leg, as it should. Try it for your self, stand up, place the foot slightly behind you and move the foot straight up, the knee will go down.

Do I miss something? Please let me know.

All the best

Hi Dr.Sassi,

Thank you very much for the prompt reply. You confirmed my assupmptions. Everything is clear now.

You’re very welcome, CaseyGregor!

My best wishes for your project.