How to CONNECT an object to ANIMATION BONES in Blender

In this arti­cle we are going to con­nect ani­ma­tion bones to a 3D mod­el so that they can deform the mod­el and ani­ma­tions can be made using frames.

Starting situation

We start with a 3D mod­el and the Arma­ture object we want to con­nect to the mod­el, you can see how to cre­ate ani­ma­tion bones in this oth­er arti­cle.

3d model with animation skeleton in blender
Fig. 1: We start from a 3D mod­el togeth­er with an ani­ma­tion skeleton.
3d model with subdivisions and animation bones in blender
Fig. 2: The 3D mod­el has sub­di­vi­sions so that the ani­ma­tion bones can deform it.

Parent 3D model to animation bones

What we have to do now is to link the 3D mod­el to the Arma­ture object, this is done by par­ent­ing them, it is impor­tant to par­ent the 3D mod­el to the ani­ma­tion bones, that is the Arma­ture object has to be the par­ent object, note that in fig­ure 3 the objects have been select­ed incor­rect­ly, in this case, the cor­rect way to select them is as shown in fig­ure 4, in which the active selec­tion is the Arma­ture object. For more details see the arti­cle on how to par­ent and un-par­ent objects in Blender.

selection of two objects in Blender, the active selection in yellow color
Fig. 3: Both objects are select¬≠ed, the active selec¬≠tion is the 3D model.
selection of two objects in Blender, the active selection in yellow color
Fig. 4: Both objects are select­ed, the active selec­tion is the ani­ma­tion skeleton.

In the win¬≠dow to par¬≠ent the objects we select one of the options with¬≠in "Arma¬≠ture Deform", each one will have dif¬≠fer¬≠ent effects, in this case we are going to use the basic form that would be "With Emp¬≠ty Groups" (fig¬≠ure 5) in which groups of ver¬≠tices are cre¬≠at¬≠ed with¬≠in the 3D mod¬≠el with the names of the bones.

Window to parent objects in Blender.
Fig. 5: Win­dow to par­ent objects in Blender.

Once the 3D mod¬≠el is linked to the ani¬≠ma¬≠tion bones, select the object and go to the win¬≠dow where the ver¬≠tex groups are locat¬≠ed by click¬≠ing on the icon shown in fig¬≠ure 7.

3d model with animation skeleton in blender
Fig. 6: Once the rela­tion­ship has been estab­lished, the 3D mod­el is selected.
vertex tab of an object in Blender
Fig. 7: Ver­tex tab of the select­ed object.

In the "Ver¬≠tex Groups" sec¬≠tion we can see the ver¬≠tex groups that have been cre¬≠at¬≠ed by link¬≠ing the mod¬≠el to the Arma¬≠ture with the "Emp¬≠ty Groups" option, at this point these ver¬≠tex groups have not been assigned any ver¬≠tex of the mod¬≠el so we are going to start assign¬≠ing them.

vertex groups to animate 3d model with animation bones in blender
Fig. 8: Ver¬≠tex groups were cre¬≠at¬≠ed with the names of the ani¬≠ma¬≠tion bones.

Select the mod­el and enter the edit mode, notice in the "Ver­tex Groups" tab that the "Weight" field appeared, which was not there before, the Weight val­ue allows us to indi­cate what per­cent­age of influ­ence will have a par­tic­u­lar bone on each ver­tex, where the val­ue 1 indi­cates total con­trol by the bone and 0 indi­cates that the bone does not have any con­trol over the vertex.

3d model with animation skeleton in blender
Fig. 9: Enter the edit mode of the object relat­ed to the Armature.
vertex groups to animate 3d model with animation bones in blender
Fig. 10: The ver¬≠tex group win¬≠dow changes slight¬≠ly in Edit Mode.

Before assign¬≠ing the ver¬≠tices to each group I am going to show the names of the bones, for that I select the Arma¬≠ture object, go to the Arma¬≠ture prop¬≠er¬≠ties and in the View¬≠port Dis¬≠play win¬≠dow check the "Show Names" box as shown in fig¬≠ure 11.

option to display object names in the blender viewport
Fig. 11: Acti­vate this option to dis­play the names of the ani­ma­tion bones in the Viewport.

CHECK OUT THIS CRAZY EXPERIMENT

Assigning vertices to bones

We are going to select the ver¬≠tices at the top of the 3D mod¬≠el, those shown in Fig¬≠ure 12.


A set of vertices is selected to link to an animation bone in blender.
Fig. 12: A set of ver¬≠tices is select¬≠ed to link to an ani¬≠ma¬≠tion bone.

Con los v√©r¬≠tices selec¬≠ciona¬≠dos vamos a la ven¬≠tana "Ver¬≠tex Groups" y selec¬≠cionamos el grupo al cual asig¬≠nar los v√©r¬≠tices, en este caso el grupo "Bone.001" y acto segui¬≠do pul¬≠samos el bot√≥n "Assign" que se mues¬≠tra en la figu¬≠ra 14.

vertex groups to animate 3d model with animation bones in blender
Fig. 13: Select the group cor­re­spond­ing to the bone to which you want to assign these vertices.
assigning vertices to a group in Blender
Fig. 14: The select¬≠ed ver¬≠tices are assigned to the select¬≠ed group.

Test if the bone deforms the assigned vertices

Before assign¬≠ing more ver¬≠tices we can do a test to see if what we did worked, for that we select the Arma¬≠ture object and go to pose mode, as shown in fig¬≠ure 16.

animation skeleton in blender
Fig. 15: In object mode the ani­ma­tion skele­ton is selected.
pose mode in blender to animate bones
Fig. 16: Change to Pose mode to ani¬≠mate the bones.

In pose mode we select the bone and rotate it, if every¬≠thing went well we should see that the bone deforms the ver¬≠tices that were assigned to the group, as we can see in fig¬≠ure 17.

rotation of an animation bone producing deformations in a 3d model in blender
Fig. 17: When rotat­ing a bone in Pose mode, the linked ver­tices rotate together.

Assigning the remaining vertices to the animation bones

Now we are going to select the ver­tices of the low­er part of the mod­el which will be total­ly con­trolled by the bone at the bottom.

A set of vertices is selected to link to an animation bone in blender.
Fig. 18: The assign¬≠ment process is repeat¬≠ed for the ver¬≠tices below.

Vamos a la ven­tana "Ver­tex Groups", selec­cionamos el grupo cor­re­spon­di­ente y hace­mos clic en el botón asignar.

vertex groups to animate 3d model with animation bones in blender
Fig. 19: Now the group cor­re­spond­ing to the low­er bone is selected.
assigning vertices to a group in Blender
Fig. 20: The select¬≠ed ver¬≠tices are assigned to the select¬≠ed group.

Make two animation bones control a group of vertices

For the remain­ing ver­tex loop what we are going to do is that both bones can con­trol the ver­tices, for this we have to repeat the pre­vi­ous process but change the Weight para­me­ter. We start by select­ing the set of ver­tices, a quick way to select an Edge Loop is by press­ing ALT and click­ing on one of the edges of the loop we want to select.

A set of vertices is selected to link to an animation bone in blender.
Fig. 21: The ver­tices in the mid­dle that are at the same dis­tance from both bones are selected.

Then go to the "Ver­tex Groups" win­dow and change the Weight val­ue to 0.5.

field to select the weight or influence that an animation bone will have on a set of vertices in Blender.
Fig. 22: Change the weight with which the ver­tices are assigned.
field to select the weight or influence that an animation bone will have on a set of vertices in Blender.
Fig. 23: The weight is set to half.

Then we select the first group and assign the select¬≠ed ver¬≠tices to it.

vertex groups to animate 3d model with animation bones in blender
Fig. 24: The first group of ver­tices is selected.
assigning vertices to a group in Blender
Fig. 25: The select­ed ver­tices are assigned to the group with the pre­vi­ous­ly select­ed weight.

Then we select the sec¬≠ond group and also assign the select¬≠ed ver¬≠tices to that oth¬≠er group.

vertex groups to animate 3d model with animation bones in blender
Fig. 26: The sec­ond group of ver­tices is selected.
assigning vertices to a group in Blender
Fig. 27: The select­ed ver­tices are assigned to the group with the pre­vi­ous­ly select­ed weight.

As the ver¬≠tices were assigned to both groups in each of them with weight equal to 0.5 with this we have estab¬≠lished that each bone will have a 50% influ¬≠ence on these ver¬≠tices. In Fig¬≠ure 28 you can see the result of all this.

rotation of an animation bone producing deformations in a 3d model in blender
Fig. 28: The ver¬≠tices of the mid¬≠dle respond to both ani¬≠ma¬≠tion bones.

One thing that could have been done is to assign the inter¬≠me¬≠di¬≠ate ver¬≠tices weights of 0.25‚Äď0.75 in each cor¬≠re¬≠spond¬≠ing group.

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