XM Magdalena 3D print, GGeorgy (3D)
LC #42 Pipers Alley

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03-01-2006, 11:37 AM

Have modelled and FK rigged a Transformer toy robot and have got the FK rig working fine and he transforms into his plane which i have set up to be controlled by sliders.

BUT I am having trouble figuring out any way of setting up his legs with IK.

The trouble is that along the leg joint chain, each joint can only rotate about one axis because of the way the toy is made. Also the rotations differ along the chain too - this should be clearer in the attached images.

I am jus a bit mind boggled as to where i would put my IK handles to control the leg without it breaking the restrictions of the joints.

Anyone think this is actually doable? Would be very grateful for any help.

At least he transforms but want to make him walk!


03-02-2006, 12:30 AM
ah yes, the joy of IK rigging robotic parts with multiple joints.

IMPORTANT NOTE: This is only good if you're using Maya as I don't know squat about rigging in Max, Lightwave, XSI, etc.

Okay, here's how I *think* you can do this. My friend, you will first have to open up the Pivot Limit Information tab for each joint so you can turn off the degrees of freedom (be sure to keep the desired degree of freedom on the axis for each joint to rotate on). Next run an IK handle linking the hip (rotate on z only), to the ankle (call this "LegIK"). After that, you will run another IK from the hip (rotate on x) to the hip (rotate on z) (call this "HipIK"). Open up your hypergraph and first group LegIK (rename to "LegGIK" or whatever you wish to call this), and then snap the pivot to hip (rotate on x only). Next select Hip IK and create a group, then snap the pivot to hip (rotate on z only).

Create a nurbs circle and call it "foot controller" and snap it to one of the foot joints. Grab both LegGIK and HipGIK and parent them to the foot. I think that might help you.

Oh, and by the way, nice Starscream model. I see he's based of the Galaxy Force / Cybertron toy. I've got to say that's he's my all time favorite Decepticon.

03-04-2006, 11:24 AM

Thanks very much thats really helped! Yea it seems to have done the trick. :thumbsup:

I checked out your Mighty Megatron model and it looks really nice. Did he ever get animated? Glad you like my model, hopefully now I can make him run and jump into his tranformation. Need to get hold of the classic transform sound effect :)

Oh actually, one more question about the rig - do you know how I would set up reverse foot kinematics with the rig?

Thank again so much for your help! Much appreciated.


03-07-2006, 11:05 PM
hey Alison, I'm glad that the advice I gave worked out for you. In regards to the feet, I have an idea on how to rectify that problem, but I'll have to post it tomorrow.

03-09-2006, 01:14 AM
Okay, here's the lowdown for doing the part that comes out of the foot. What you're going to do is first parent the bone for that part to the NURBS circle that you made earlier for the foot controller. This will break the bone chain right there which is what you want because you don't want the IK effecting that joint. Create a new NURBS circle called "hidden weapon" or whatever it is that folds out, and snap it to the joint. Open up connections editor and load "hidden weapon" into INPUTS and the joint into OUTPUTS. Select rotate on X for both under ROTATE tab. Parent "hidden weapon" to the joint.

Now just go into the attributes editor and add attribute to the foot controller (call it unfold) give it a default of 0, minimum of 0 and maximum of 5, press okay.

Then go into set driven key editor. Load up the foot controller in Driver box, and then select the unfold attribute in the box next to it. Next, select "hidden weapon", and then put it in the Driven box (below the driver box). Select rotate x. Hit "Key" now select the unfold attribute, and change the value to 5. Go to the hidden weapon circle, rotate on x to the desired position, and then set the key.

After this, you should be done.

03-15-2006, 11:02 AM
Thanks so much for your help. :thumbsup:

Have been very busy with my degree project recently but once thats over il be able to start animating him. Will upload the turnaround of the model with him transforming when i get hold of some webspace.

Cheers again for solving these rigging issues. Much appreciated


03-15-2006, 07:19 PM
hey, no problem Allison. I remember how much of a pain it was to figure out the IK to my own Starscream model. Luckily, I had some help from one of my animation professors, so I'm just as happy to pass along what knowledge I do have on the subject. Good luck with animating!

03-23-2006, 12:19 PM

I thought i'd post the turnaround of my Starscream model, which shows it transforming. The project is on hold for a bit while I work on my degree project but am looking forward to animating him properly.

http://www.savefile.com/files/8565713 (http://www.savefile.com/files/8565713)
Thanks for passing on your knowledge again. Hope you like the turnaround :) ,


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