Hi,

Say you have two bones -- bone1 and bone2 -- and your in top view. Bone1 has its roll handle pointed forward, bone2 has its roll handle pointed back. I need an expression on bone2 so that, if I move bone1 forward, bone2 will move an equal distance backward.

I would have thought that I just create an expression on bone2's Y transformation and in that expression I would just place the Y transformation of bone1. But no, that's wrong, this doesn't work.

Does anyone know what type of expression I'd need?

Thanks!
Rusty

Is it possible to set up a constraint that has a negative enforcement percentage?

I'm not experienced with A:M expressions but I would have thought that if you had two bones, front_bone and back_bone, and you created an expression for the z position of back bone to be "=0-GetWorldPo(front_bone,z) that it would work but I just tried it and it doesn't work in 13t. This is more than likely because I don't understand what the corect synatx should be. Searching for info on expressions didn't turn up any clues either.

It's actually quite simple, add this expression to the TranslateY property of bone 2: -..|..|..|..|Bone1.Transform.Translate.Y
Or of course an other property...

Ooh! Thank you, Luuk!

Rusty
this sample has roll handles pointed opposite z directions and the points are in opposite y directions only the x positions are the same
so the expression would only have to be the bone1 postion in the y and z direction and the negative position in the x direction in the appropriate directions to move bone2. bone 1 is on top in this example


I set this up for all directions

Click to view attachment Click to view attachment



V14b project

Click to view attachment

Hey everyone... thanks for trying to help me out on this!

Okay, my expression was correct but nothing else was... I guess. I thought that you simply right clicked on the item you wished to put the formula on (i.e. bone1's Y translation)... IN THE MODELING WINDOW... IN THE BONE's Folder and selected 'Edit Expression' and then clicked on bone2's Y translation and, after that it was attached to the model and would work in actions and chors. This is simple enough to do but... I guess that's not the way it's done. Hm... how come AM lets you do it this way if it is meaningless???

Looking at John3D's (thanks John!!) example project... he created an off/on pose relationship and created the expressions in that (as you do with constraints and such). Okay, makes sense. However... when I right click on the bone and select edit expression... how or where do I click on bone2's Y translation??? I certainly don't want to type all that in (wouldn't know how to anyway). So... John can you make a video of you creating these expressions?

Thanks!
Rusty

Rusty

Not sure if you need a video. All I did was set up the a new pose went to the action area where you adjust the pose and opened the translate area for each bone. Then on bone 2 z translate I selected edit expression then clicked on the translate z section of bone 1 and what you see in the expression appeared. The same for each direction then because of how the bones were placed I added the *-1 to the x direction expression. If you still need a video I could do that my paypal....just ask

John

Well, I tried to do this but I could not get the translate z section of bone 1 to appear in the action to select it. ??? Maybe a few screen shots would let me see how you are doing this.

thanks,
Rusty

Okay here is the no sound demo. I did not change the x direction to be negative and you'll notice that in the first demo of the pose but the y and z work when I switch views

Click to view attachment

Does this help ?


john

Well, LOL you video starts off with the relationship open and everything you need visible! I guess its just a matter of placing key frames on the bones in the relationship (so they are visible), make your expressions and then remove the key frames. Except I tried this and the darn bone2 properties did not become visible. But I'll try again... can't be that hard.

Thanks,
Rusty

I started it after starting a new pose. then went to the relationship opened what bones would be effected and just added the expression. I set it up to be quick because of the size factor of the video. The bones only must be available in the pws in the action/relationwindow and the expression shows it the model relationship area above the action/relationship setup area. Hope this helps