reverse foot roll

[TheUsualAlex]

Has anyone tried reverse foot roll in Houdini's IK yet?

[miguel m]

If I knew what's that... must be some maya concept, I guess.

[michael]

yeah...reverse foot is a maya thing...

Alex > why would you want to do a reverse foot in Houdini?

[TheUsualAlex]

Hey Arctor,

Actually, I have no idea why I would want it... I've only seen people use it, but I can't think of and advantage over the simpler version of the foot-roll set up... So I was wondering if anyone has done something for it in Houdini.

[stu]

Yup. Two bones - one running from the heel to the ball of the foot, and another running in the opposite direction in parallel.

stu

[TheUsualAlex]

Hi Stu,

What is the advantage of using the reverse foot roll vs. just the regular set up of using 2 bones on the foot only? (I've only done the latter one, tho...)

Thanks.

Alex

[betty]

i've use reverse foot and found it to be great. easy to use once set up. just when i got started with houdini i was doing skeletal setups and such and remember doing a reverse foot. i like them. i've seen other two bone setups doing the same thing but one would have to set up more constraints with expressions and such. that was from my quick observation. but i also haven't seen a character set up by a houdini pro so i don't really know the better methods for houdini. the two bone set ups that i have seen set up where in maya and xsi.

b

[stu]

The advantage to a reverse bone foot setup lies in that the pivot point in the foot upon which the weight of a character is entirely supported can be animated properly. When you walk and you put your foot down your heel supports all of the weight but as you continue, your weight gradually moves to the ball of your foot. Thus the pivot moves from the heel to the ball and sometimes all the way to the toes on the foot in contact with the ground during a stride. A normal foot setup doesn't allow for this, (typically the pivot remains at the heel) as evedenced by a lot of animated walks up until fairly recently. The reverse bone setup does allow for this, and the difference is really pretty amazing.

stu

[TheUsualAlex]

I see. Thank you, Stu. I'll give that set up a try once this school quarter is done.

(there goes my list of things to do...)

Alex

[betty]

stu

yep the pivot thing, when i've seen two bone setups act like the reverse foot setup they will have an if condition, so if the ankle rotates more than x then the pivot will jump to the ball and so on. so the pivot will be tied to expressions and constraints will be added as well.

so even though the two bone setup looks simpler it needs more ( ie, expressions and constraints ) and can do the same thing from what i've seen.

b

[thekenny]

actually, most animators on the floor complain every time something is automaically rigged. so i've found that although it might look really cool from a setup point of view, it just will be undone later on. if you do leave in that kind of automatic behaviour in your rigs you should really consider a way to either counter it, or turn it off.

i've found the biggest thing working with feet in general that you need to break the rotations from the leg/hip bones above. the will cause you to twist the ankle/feet and it will be more work to clean up then anything.

an object blend will allow you to filter out those rotations, you just have to becareful how you rig it up.

the cool thing about houdini is you don't have to do the backward pointing bones of the maya reverse foot setup. like always there's more than one solution in houdini.

-k

[TheUsualAlex]

Hi Kenny,

Wow. I have no idea that such were the production environment.

I gather that you just use the regular, 2-bone set up instead of the reverse foot roll?

Speaking of obj. blend, did you actually successfully do the switch with obj. blend? A while back in the summer I was trying to figure out a way to do ik/fk switch using the obj. blend. I've only gotten it to work on matching up 1 rotation axis. But when it comes to multiple rotation axis, the set up would just went berserk.

Until Edward Lam showed me his set up from CHOP, which I really liked! Edward's was using only 2 sets of bones instead of 3 that I've been taught.

--Alex

[thekenny]

it is a two bone set up but it still acts in the same manner as a reverse foot setup. i'd have to set up a file to submit it for it to be clear on how it works. but you can do it with single bone ik chains. you just have to tricky in how you do the parenting of the goals. you still do rotations to do the foot roll properly. it also uses the twist effector to handle the level planting of the foot. you will still run into the 180+ flipping though, you just have to wary of where stick the twist goal.

i'll see if i can post a hip for the gang here in the near future.

as far as the ik/fk switching. ed's file is fine. i've played with it to do as you mention, so you see the three bones. the ik, the nok (which is what we generally call fk), and the destination bones. which would be doing the deformations. it is just personal perference, neither is better than the other. ed's might be a bit faster though

i don't generally use the blendObj for switching as you describe, although that's what is meant for. i had described is use in a previous post. check thru the character list, let me know if you need more of an explaination. if used correctly the blendObj can filter out the rotations of one parent and pass the rotations of master null. the endresult is a foot set up that is in the same hierarchy and the foot doesn't inherit the parents rotations. so if your twist the knee out to do that good ole cowboy walk the foot stay planted.

enjoy.

-k