How to Auto Foot Roll?

Hi all!
I’m trying to create a simple IK leg rig for Lego Groot with no ankle joint and just a knee. I need the foot to auto roll onto toes when hips go down. I sort of have a working rig, it’s just laggy most likely due to circular parenting or constraints. If anyone knows what I’m doing wrong, or a better way to do it, the blend file is linked below. Thanks!

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Not totally sure how you want to control this, because the file of course has a dependency loop.

It sounds to me like you want a “rotate to floor”-- you want the toe to get floored. This isn’t (reasonably) doable with constraints alone, but it’s doable with drivers. Here, because I don’t like recreating constraints in drivers, I’m using a combination of drivers and constraints:

flooredToe.blend (831.7 KB)


hey thanks for trying to come up with a solution! its not quite what i’m trying to do tho. see video below. basically the groot lego model has a weird leg thing where he only has hips and knee joints. and no “foot”. which leads to a ton of feet intersections with the ground. the only fix i can think of is to have him auto roll onto the tips of his feet when the hips are lowered. any chance drivers could do this? I’m not too familiar with drivers. if there’s a better way to rig this type of leg with IK I’d love to hear it!

I don’t think you’ve given us enough material inside the blend file for us to make an informed suggestion though. It’s kind of hard to see what you’re going after with the provided blend file as of right now. However it seems to me that you’re still new to rigging, and if you’re interested to make a functional and robust rig for your Groot model, I can help you with that.

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Hey Sandtail i’m definitely not a pro at rigging thats why im here! Let me know what else you guys need to know. Basically i have the functionality i want in the blend rig i just need to figure out how to either fix the dependency loop or how to rerig it entirely to achieve the same thing. When the hips are lowered, the feet auto roll onto toes. thats what i need it to do.
I appreciate any and all help!

In order to help you better, we would need a better file to look at. Start by naming your bones, so anyone looking at the file knows what each bone it for. You might also want to post up part of the mesh too. I understand there is no ankle, but are there toes that can move?

Without seeing more, I can’t help much,

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Hi Randy,
Thanks for the notes. Here’s an updated leg rig blend file:

no the toes can’t move. Let me know if you guys need anything else.
Thanks for trying to help!

Hi Garrison,

Thanks for posting the updated .blend file, now I better understanding what you have going on.

So now, how about telling me what your are gonna do with this thing? Since you are rigging it, you’re planning on animating it, right? So this doesn’t make sense:

Because for a basic walk cycle, when the hips are down, one foot is on it’s toes, the other foot would have the heel contacting ground. I’m thinking for a basic walk cycle you’d want a foot controller and a foot roll controller. The foot controller would be where the foot is placed, and the roll controller would control heel to toe rocking of the foot.

So what do your really want?


P.S. I’ll be away from internet access for a few days…

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Hey Randy,
Yes the goal is to make it easy to animate. I want to animate him doing a little dance. As you can see in the video above there’s nasty feet intersections with the ground if the hips bob up and down and thats using the normal foot controller and foot roll controller. Counter animating with the foot roll control to clean up the intersections would be a pain for longer shots to get nice results. That is the only reason i am trying to automate it. if you think a normal foot and roll controls would work i’d be curious how you’d keep the feet planted flat on the ground.
I need IK legs and don’t want to bend or stretch the Lego bricks.
If you know of a better way i’d love to hear it!

Hey Garrison, sorry I’ve not got back to you before this.

So I took a look at the file you posted, I shook it up, flipped it upside down, smacked it against the wall, and bounced it of the floor a couple of times… and I’m still thinking about it…

Yes, that can be done with drivers. The foot could roll on it’s toes every time the hip is moved downwards. How would that work with

Because every time the hips go downward, both feet would roll onto the toes. To me, that would be very limiting. I mean, it might work for a dance, but it wouldn’t look right for trying to walk. So are you thinking just a short, one time dance routine, or doing more animation with it?

If it were me, I’d take some ‘artistic freedoms’ here.

I’d cut away part of the foot, shown in red, and make a linkage like I show in blue. The linkage in blue would be a lower leg bone and would ad another joint, making it a bit easier to animate.

I know it wouldn’t be 100% correct, but it would work and no one would notice. Fool the eye with good animation/lighting/rendering, and done.

Just my honest opinion,

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