# a person carries a book and puts it on a desk

I know how to group one object to another, but I just cannot imagine what would be the ideal way to organize the following animation:

A person walks through a room, and is wearing a book in his right hand.
When he reaches a desk, he throws the book on the desk and starts gesticulating with his hands.
How do I do this? As mentioned before, I know how to group two objects, but after the desk, they should be ungrouped, how would I do that? - I mean separate the connection between book and hand. Or is there a better method? Please tell me if you could help me or give me a hint!

What might be a nice way to do this is to setup a simple flat cube and the desk as a dynamic simulation. Record the physics simulation into keyframes. That way you can get a realisitc toss and fall to the desk for the book.

So to transfer the book from the character to the desk you need a CopyLocation constraint on the flat rectangle and one on the character as well. For the first part of the animation set the CopyLocation influences on the flat rectangle and the book to opposites. ie. Character 1.0 and flat rectangle 0.0. Then at the point where the book leaves the character’s hand, start cross-fading the influence values to their opposites to transfer control from the character to the flat rectangle. Because the flat rectangle already has keyframes from the simulation, once the CopyLocation influence reaches 1.0 the physcis simulation will be moving the book as well.

You can simplify that if you like. Just replace the physics simulation with a few keyframes.

I wouldn’t use physics, or CopyLocation myself, although you can do that. I’d use a ChildOf constraint on the book, animating it’s influence as you suggest, then hand animate its arc and crash onto the desk.

Thanx to both of you. Both answers sound difficult, but it is crucial to animation, so I guess I have to bite the sour apple and get started, I think Hankyman´s suggestion sounds less complicated, so I think I will start with that solution and see how it goes…

I’ve put up a full step-by-step on how to do this at harkyman.com.

Thanks for the terrific tutorial! Short and concise! That is how a good tutorial should be. And I must say that I am very happy with the result.

PS: I have got an issue though, but I am not sure whether it is related. It is when my character has fur/hair particles. He grabs a book, which is the object that has the constraint. When I click on the key button under the object´s constraint, and turn influence up to 100 for the book to follow the character´s hand, well, from that moment on, the character´s fur/hair particles disappear… If I keep influence on 0, the hair particles do not disappear.

That sounds like a bug, not anything you’re doing wrong. When you say that they disappear, have you tried a render while they’re gone? It could be that they still render, but the display is goofed up.

Well…actually it is the other way round. The particles are there in the object view, but when I render they aren´t. I was wondering if for some error typing I made the target adopt the material of the object with the constraint, but that is not the case, as the character keeps his material/texture, but without hair particles when rendered.

If your file’s not too large, could you attach it?

Thanks a lot:-) well, it was 1.35 mb, I´m struggling to get it smaller, then I will upload it here…

It is all yours… the problem occurs in around frames 155/156, i e. when he grabs the “book”, when he does that, Blender does not render the hair particles:eek: Thank you very much if you could solve this issue.:o

### Attachments

Grab_a_book2.blend (924 KB)

After looking at your file, all I can say is wow. You’ve found some kind of freaky bug. There’s nothing you did wrong in that setup to cause the behavior you’re describing. It’s just like you said. Delete the box object and everything renders fine. Truly strange. I’m going to see if this behavior persist in Blender 2.5. If so, I’ll file a bug report.

That’s definitely a glitch. It looks like it is being caused by the child of constraint… since the constraint is using the vertex group in the hand as it’s target.

@Jaqueline
To fix this in your file, set the child of constraint on the book to the hand bone instead of a vertex group.

@all
I’ve put together a file from scratch that demonstrates the bug. It’s very likely that no one has yet encountered this bug until now… because hair is typically applied to a character, a character typically has an armature, and the child of constraint would typically be applied to the armature (not the mesh).

### Attachments

childof_hair_glitch.blend (621 KB)

Thanks both of you, but how do I link it to the armature´s hand bone? there is no box for that in the constraints panel as far as I can see…

right now the child of constraint for the book reads “OB: Wolf, VG: hand.l” which refers to the vertex group you have created on the left hand. You need to change them to read “OB: Armature, BO: hand.l”. Since your hand bone is conveniently already named ‘hand.l’ you simply need to enter “Armature” in the OB: field. Notice that when you do the VG: field changed to BO:… which means it is now constrained to the hand.l bone in the armature, instead of the hand.l vertex group on the mesh

Alright, excellent. Thank you.