Rigging help

[Da_elf]

Has anyone ever rigged one of these? i need it to be able to still function properly even when the join angle changes. im assuming i need to use a rotation expression to keep one piece rotating the same angle as the other in the z-axis.

[kimgar]

A colleague of mine who is a great A-Ford enthusiast, made a quick sketch of your problem. i guess you already know how it works, but i could not resist posting his sketch



i'm no rigging expert, but seems that you could just set the axes at the middle 'X' thingy and translate the main z-rotation to the secondary with some wiring perhaps?

i remember rigging a truck a long time ago like this, think i solved it with a 1-bone system...

[ene.xis]

i surely have no idea...but he might help you out:
http://www.vrayelite.com/tractor.php

[Da_elf]

indeed i know how it works. ive got a degree in mechanical engineering but im trying to get it to work in 3d now. I couldnt see if the tractor had a working u-joint on it and the tutorial on that site was about the materials not the making of

[joconnell]

For anything like this you can add in extra nulls in the parent chain to stop stuff freaking out - I take it that the plate mounted on the cylinder rotates along the length of the cylinder, the first hinge is up and down as we're looking at the picture and the last part rotates in and out of the picture?

In my experience things will generally behave if they don't have to rotate too far off their parent. If you tried to rig this straight, I'd say having the disc rotated 270 degrees and then trying to hinge the next part will make it freak out so if you find that there's a section going mad, try and align a null to the hinge going mad, parent the hinge to the null and then the null to the hinges old parent so rather than this as your chain:

arm > disc > hinge 1 > hinge 2

You'd have:

Arm > null > disc > Null > Hinge 1 > Null > Hinge 2

This just means that you're isolating the amount each joint is rotating relative to it's parent each time which will give you less chances of it freaking out.

Another option would be to parent everything normally and then use freeze transforms to rest each objects rotation which will normally make things behave better - it's kind of doing the same thing as above except it's doing it by leaving the first rotation controller with the values as parented and then adding a list controller with a fresh rotation controller layered on top with a value of 0,0,0 which makes it a lot less likely to get freaked out at the further reaches of rotations.

[Da_elf]

one of the things i need is for the cross piece to be able to have two look at constraints. i need it to look at an object with only 1 of its axis and then the other look at axis is looking at another object. so far look at only lets you constrain all the axis...

EDIT...
Nevermind, i found a work around thats crude but efective

[kimgar]

hmm, i think i managed to do sort of something you are asking for, if you create a 1 bone system with 'assign to children' ticked and IKHI solver, link the bone to the rotating arm, the other arm to the bone, and the end effector to a path or whatever, it seems to rotate the way it should - but then again, with my kind of technical knowledge, who knows



anyway, a bit hard to explain, you can have a look at the scene here if you want:

http://www.indok.no/filetransfer/temp/aksling.max

max9 64bit, though...

[Da_elf]

ok. its finished. i just used look at constraints in the proper places and then faked the cross piece the same way kimgar did by using 2 pieces. i was trying to do it using 1 piece at first but that was proving to be difficult since i couldnt constrain one rotational axis to one object and another rotationalaxis to another object

http://www.elfpro3d.com/Turtles/Ujoint.avi

[kimgar]

hah, that is cool - faking is always good!

look at constraints was my first idea aswell, but i could not get the second arm to inherit any rotation as it was reset by the constraint...but of course, i guess you could fake that as well

nice job elf, keep it up!

[Da_elf]

all the arms are controlled via expressions. when the wheel of the jeep turns it in turn causes all of the linking arms to rotate

[posterus]

hmm interesting we all went about this in different ways. here is my version of the u-joint (this clip is different from the one on vrayelite): http://www.joepizzini.com/VRAY/Tractor/tractor.html the u-join animation is at the end of the clip. what i did was have the whole u-jount assembly and the attached arms laid out straight. from there i gave it some longitudinal rotation keys. if i needed to edit the longitudinal rotation speed of the arms i simply copy/edit the value of the key. the other rotations (at the u-joint pivots) were done with linked dummies...this is kind of hard to explain...i remember it took me awhile just to wrap my brain around the motion of it.
best
-joe