Question about skeletal construction - arms
polycounter lvl 18
hey folks. i'm trying to do what XSI users might call setting up a counter-rotation null on an arm bone.
if you hold your forearm out in front of you, with your uper arm down, and rotate your upper arm so that your forearm swings out, you'll notice that your upper arm by your shoulder moves not at all, but your upper arm by your elbow moves 100%. this would be the upper arm's X axis.
if i was using xsi to rig, i'd bring in a null (in max, you'd call it a point,) match it up perfectly with the upper arm bone, and parrent it to that bone. i'd possition it so that it's neer the shoulder, and i then write an expression that says the X rotation of that point = the negative x rotation of the upper arm bone.
that way, the point will rotate on y and z with the upper arm bone, but it won't rotate on x-- that is, in the case where your forearm sticks out in front of you, and you rotate your arm out, the point at the shoulder will not rotate at all.
i then weight the arm so that the top of the arm neer the shoulder is weighted to that point, and the bottom of the upper arm neer the elbow is weighted to the actual arm bone.
then when the bone is rotated on x, you get a proper rotation.
does anyone have any idea how i'd get this effect in max?
thanks alot.
btw, i may write a tutorial on building a simple character rig in max, with nice pictures in a simple, easy to understand manner.
this is the only thing i dont know how to do when setting up a basic rig.
if you hold your forearm out in front of you, with your uper arm down, and rotate your upper arm so that your forearm swings out, you'll notice that your upper arm by your shoulder moves not at all, but your upper arm by your elbow moves 100%. this would be the upper arm's X axis.
if i was using xsi to rig, i'd bring in a null (in max, you'd call it a point,) match it up perfectly with the upper arm bone, and parrent it to that bone. i'd possition it so that it's neer the shoulder, and i then write an expression that says the X rotation of that point = the negative x rotation of the upper arm bone.
that way, the point will rotate on y and z with the upper arm bone, but it won't rotate on x-- that is, in the case where your forearm sticks out in front of you, and you rotate your arm out, the point at the shoulder will not rotate at all.
i then weight the arm so that the top of the arm neer the shoulder is weighted to that point, and the bottom of the upper arm neer the elbow is weighted to the actual arm bone.
then when the bone is rotated on x, you get a proper rotation.
does anyone have any idea how i'd get this effect in max?
thanks alot.
btw, i may write a tutorial on building a simple character rig in max, with nice pictures in a simple, easy to understand manner.
this is the only thing i dont know how to do when setting up a basic rig.
Replies
i make the bone a parent of the point.
i grab the point, right click, go to wire parametres, select the appropriet rotation axis, and then click on the bone, select it's rotation. in the window that pops up, i select the one way arrow thing pointing from the bone to the point, so that the bone's x axis should now drive the point's y axis. (the point and the bone's axis aren't aligned, simply because i drew the bone in the left viewport, so the point's y axis is the same as the bone's x asis)
now when i rotate the bone on only one axis at a time, it works ppppeerrfectly. when i rotate on one axis, and then a seccond one, however, the y axis of the point starts rotating.. grrrrr.
does this have anything to do with gimbal lock and the rotation order?