PDA

View Full Version : realistic forearm rig


Soeren Nielsen
01-12-2003, 03:28 AM
Anyone ever had the luck of rigging a forearm by mimic'ing the real world. (using the ulna and radius bones)
Been trying to get this to work, but with no luck, its like the wrist thins out when using this. Any help would be appreciated

CIM
01-12-2003, 03:37 AM
Have two bones for the forearm that twist with the wrist bone (use an expression(s) to make them follow). The first bone (up from the wrist) should follow about 50%, while the next one follows like 25%.

Eugeny
01-12-2003, 05:18 AM
Originally posted by Soeren Nielsen
Anyone ever had the luck of rigging a forearm by mimic'ing the real world. (using the ulna and radius bones)
Been trying to get this to work, but with no luck, its like the wrist thins out when using this. Any help would be appreciated
I tried this and get some pretty good result as ell as conclusion that the splited forearm bone is easier, but if u interesting ill post the file later ...

faulknermano
01-12-2003, 05:26 AM
Originally posted by Soeren Nielsen
Anyone ever had the luck of rigging a forearm by mimic'ing the real world. (using the ulna and radius bones)
Been trying to get this to work, but with no luck, its like the wrist thins out when using this. Any help would be appreciated

the thing you should remember is that the ulna and radius bones influence the skin greatest near the wrist. towards near the elbow, the influence goes to nearly zero (but not quite).

this is what i did, generally speaking..

first i have an ulna and radius bone. the ulna bone corresponds to the real life ulna bone and should be placed accordingly. the radius bone is a combination of the radius bone influence PLUS the brachiaoradialis muscle. so, what i did was to place the root of the 'radius' bone where the brach. muscle 'starts' within the segment of the forearm (because in real-life, the brach. muslce starts at the lower part of the humerus).

from here you create nulls and parent them on your wrist (the one that turns the wrist). these nulls will serve as targets (or goals, depending which you want) to that the two bones will twist along with the wrist while maintaining their position near the elbow.

you will lose less volume near the middle of the forearm using this method, but this isnt enough... at least it wasnt enough for me. i was losing volume near the wrist this time. so what i did was create a couple of 'support' bones to keep the shape of the portion near the wrists. i placed about six (two on top, one at the medial end of the radius, one at the medial end of the ulna, and another two at the bottom). these support bones were parented to the wrist as well and were restlength'd to about one-fourth the length of the forearm, staritng from the wrist.

i also found out that creating those support bones, with that restlength created a better looking twist at the middle of the arm, because those support bones were balancing the tendency of the radius bones to drop and sink as the forearm twists inwards (e.g. prone) since they are targeted to the wrist.

be sure to check for forearm bent rotation as well.. sometimes the placement of bones for twisting will not lead well when the forearm is rotated to flex towards the bicep. you may have to reposition alot of bones at the end.

anyway, i hope that's clear and it helps some.

faulknermano
01-12-2003, 05:31 AM
and one more suggestion: the wrist/ulna/radius can twist to about 90 degrees. for some reason i cant say right now, it's easier to supine (twist outward) a forearm than to prone it (twist inward). when i mean easier, i mean that the deformations seem easier to 'predict' or control. so make sure that your model's forearm is almost near the prone position (if you use that standard arm-high-by-the-side model then that's fine).

Mangled Poly
01-12-2003, 05:38 AM
Mike RB had a really good one....
check out:
http://www.cgtalk.com/showthread.php?s=&threadid=28922
its the arm 3 posts down

CGTalk Moderation
01-14-2006, 04:02 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.