Link constraint & IK issue

[Anonymous]

I have an animation where I use IK sliding /planted keys for the hand (to lock in place).

after doing that, I added link constraint to the same hand (for a earlier frame in the timeline), to follow the knee.

I learned that it messed up the IK sliding /planted keys I did before I went to do the link constraint.

how do I use link constraint without disrtoying the IK sliding/planted keys that come later in the timeline ?

tnx

[ads_royje]

Hi @Anonymous,

I suppose this is with Biped rig, because of Planted / Sliding Key reference, is that right ?

What I am not sure I fully understand, is the Link Constraint to follow the Knee.

Is that the Max "Link Constraint" or are you referring to the Biped IK Object  ?

If you are using the Biped IK Object, IK keys, like "Planted", "Sliding" and "Join To Previous IK Key" will get undone as the IK reference changed.

Is that the case ?

[Anonymous]

the IK planted key and sliding key got undone, even when I used the "object" (of the knee) at the prior frame.

for ex. when I animated at frame 100-200 the hand planted to ground, it works.

then I went to frame 80-96 and used the Object option (of the knee) within IK key roll, and it worked.

but it distroyed the previous anim using planted or sliding

any ideas ?

at first I used link constraint (menu bar) but since it did destroyed the previously done planted key I just used the Object option. but without success.

[ads_royje]

Sorry for such a delay in response.

The Biped "Object" option :

Triggers this message box on assigning an Object to it. That is expected, this will get the Sliding / Planted keys to regular body FK keys.

The object should be assigned before doing those keys or edit the keys again after assigning the object.

A single object can be set per Limb, the object can be changed, but can only be a single object per animation. Each time the object is changed, the Keys will be reverted to regular FK keys.

This is because the IK reference system (the object) can only be one reference system.

When attaching Biped via this method, Biped limb (hand or feet) will follow the object, the object does not follow the Biped.

If you want the Object to follow the Biped, the set up will be different.

The Max object will have to use either a Link Constraint or a Position and or a Orientation constraint.

I do hope this can help why sliding / Planted keys can get undone.

[Anonymous]

thanks alot. I was not aware that teh Object needs to be done before the other IK sliding/planted keys are done.

so, you mentioned "The object should be assigned before doing those keys or edit the keys again after assigning the object."

but how do I edit the key (or redo the sliding /planted keys afterwards ?

cause when I try to redo them afterwards, I am unable to disregard the Object (use Body instead) or alternativly use Object with 0 as the IK blend.

[Anonymous]

just noticed the video now, thanks alot for it. unfortunatly what I try to acheive is different. and its this:

there's an animation where biped stands on his hands, so I planted keys to make them not move.

then I scrolled backwars in timelne /frames, to animation where the hands follow the knees (as biped sits). used Object from hands to knees.

and the issue I have is the later animation (one I did first) has been destroyed (hands are swimming and not planted anymore when Biped does stand on hands. hope that helps.

so, since I was suppose to do the Object first, before the planted keys, how can I fix this ?

[Anonymous]

Basically your problem is that Biped only can have one single IK-target, you can`t switch targets on the fly during animation.

So you have to use a workaround to make this happen:

1)Create point helper objects for the biped hands.

2) Create a link constraint for each of the the point helper.

3) Select the point helpers as IK-targets for each hand(object), set Planted Key for hands

4) The point helpers link constraint should be set to world.

5) At the frame where the hands should be attached to the knee, select the knee as target for link constraint and animate the helper moving to the knee.

6) Set a sliding key for the hand.Now the hand should follow the knee motion.

Using a helper object with link constraint as IK-target allows you to attach to as many objects during animation as you like. It also allows for an anmiated pivot point during animation.

Hope this makes sense somehow.

[Anonymous]

Thanks, but not sure where I got it wrong, so I’ll describe what I did…

-created a point helper, placed it on the knee.

-link constraint the point helper to the knee (linked to knee at start/end frames it should follow, and to world before and after the.)

-selected a hand, at first frame that needs move with knee I set a planted key (with object as point helper) and moved it to location on knee. and at last frame needs to move with knee I set a sliding key (with object as point helper). frame before and after those I set “set key”.

now hands move with knee. however, later in the animation where I had a planted key for the hand to lock on the ground, now the hand swims…

but I was able to redo that animation (where the hands lock on ground, by simple planted key and then sliding key), it works and keeps the first anim of the knee.

now, what is it that I am doing wrong, since it seems that you meant that I do not need to redo that second animation with your method !?

tnx

[Anonymous]

Here, i made a test scene for you to investigate the process. I saved it in 2016 format.

There is indeed something glitching here. In the process of making this, sometimes the helper still followed the knee, even when linked to world or the ground plane when adjusting the biped interactively in the viewport. But then when i scrubbed through the timeline the glitch was gone. Odd.

Still, here it is:

[Anonymous]

Thanks ! sure seems to work, your file.

process wise, does the process I describe sounds right though ??

[Anonymous · Accepted solution]

Ok, let`s recap the process:

1) Create Point helper and link constraint. At frame zero. Point helper->Link constraint->Add link->Knee.

2) Biped->Key Info->Object->Select the point helper. Set Planted/Sliding Key.

3) Move to frame where hand makes contact with ground. Point helper->Link constraint->Add link->GroundBox (Link to World should work too.)

4) Animate the Point helper moving to ground.

4)Biped->Key Info-> Sliding key. 

5) Since the biped hand is following the point helper, and the point helper is linked to the ground Box, you can simply continue with your animation and the hand will stay where you placed the point helper.

The problem is the glitch i described in my earlier post, where it look like the point helper is still linked to the knee, while it isn`t.

[Anonymous · Accepted solution]

Thanks alot man, I appreacite it ! 🙂

great workaround there...