View Full Version : huge revelation - just found out how to really lock a joint so it really stays there

08 August 2006, 12:12 PM
I mean "so it stays there" not "almost stays there" :scream:
I was using auxiliary effectors to pin down the feet and keep them from sliding, but weird things were happening anyway and the feet kept sliding, maybe because of animation layers, maybe for some other reason, I don't know, I'm new to MB. oh, and even in the online demos, when they present the aux effectors in that video of the 2 girls fighting, they don't manage to lock that foot down properly. and they say something like (don't remember the exact words) "well it's sort of pinned down now, better than it was before"... and I was like "arrrrgh" people can't use "sort of" when they need to lock things down.

so my revelation - use all needed auxiliary effectors on a separate layer, key when you need them to go on/off (here it took me a while to realize you key in the Character Controls window - Reach T and Reach R, by clicking the K buttons, not with normal keys), make sure you don't do things like extending the leg too much so it moves the foot out of place anyway, no matter what you'd do, and here's the trick:

on that same layer, set a key (normal timeline keyframe) on every frame where you have active auxiliary effectors!!!

when you do this, MB automatically repositions the rig, frame by frame, to follow the aux effectors properly. of course, you might not need to do this if things work, and they sometimes work, I try to pose in such a way that I don't even need aux effectors. but many times I do, and this cheap trick does the job :)

08 August 2006, 09:38 AM
OK the reason that motionbuilder "sort of" plants the keys when you add in an Aux effector is because it's also still being influenced by the IK effector.

One of the fundamental things to remember when dealing with Motionbuilder, and this is usually the part that people forget when they don't understand why some problem with their animation is happening, is that it's like there are multiple characters with different animations running on them (the IK rig, the FK rig, the actor, constraints, auxiliaries, etc), all running concurrently, and the reach sliders, the control rig input options, constraints, and auxiliary effectors, are just dictating which pieces of which animations you're using to make up the actual animation that's visible on screen.

When you apply an auxiliary effector it has a reach slider that goes between 0 and 100 for both translation and rotation. However if you right click on the auxiliary effector in the character controls window and select the IK effector, you should see that that also has translation and rotation reach sliders that go between 0 and 100. Alot of the time, when you apply an auxiliary effector onto something like the ankle IK effector, that ankle IK effector will still be set to 100. As such you have the 100 reach of the ankle effector, mixing with the 100 reach of the auxiliary effector, meaning that essentially, each has a 100 share of 200 worth of influence, or 50% each.

Put simply, if you want to lock something to the auxiliary effector, all you have to do is turn the translation and rotation reach of the IK effector down to 0 for those frames where you want it locked, so that the auxiliary effector has a 100% share of the influence. You'll probably want to check this in your curves as it's easier to make out the spaces where the reach is affecting it or not, and it avoids problems where you're only turning down the reach for a single frame in situations where you've plotted keys previously.

Anyway, this is actually a very long-winded explanation of something very simple, so don't be daunted by all this text; it actually only takes about 5 seconds to do this.

08 August 2006, 03:52 PM
Thanks for the explanations Headless, I had a slight feeling that this could be something related to MB's layering possibilities, but I havent' actually thought of the separate rigs. My way might not be the right way to do it, but it sure is more interactive :) I mean, I find it simpler, because when I'm animating I prefer not to have to deal with any kind of other interface except for what's on screen, nor tweak too many extra-knobs, if possible, of course. The ideal animation workflow for me is one that allows me to focus on animation, while paying minimum attention to what the software is doing. Of course, one has to learn the soft and use the technology, but if the technology can allow me to use it effectively without paying too much attention to it, and not getting sidetracked by technicalities, so much for the better ;) (also the ideal animation software would be one that focuses on animation, in my case, character animation. MB is not, but it still is the best solution I could find yet. I'm looking forward to Reflex (

08 August 2006, 07:35 PM
To any Python Scripters,..... Could somebody please write something that will automate this step. People are always going to need to lock feet to the floor. A button that Creates the AUX then turns down the ik effector to zero... then another button that does the reverse. This should be something that motionbuilder has built into it, but for some reason it doesn't. It takes way too long to lock feet to the ground.


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08 August 2006, 07:35 PM
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