Rigging an assembly line robot

Introduction. The assembly line is perhaps the most impor-tant development in the manufacturing process and the industrial revolution. This manufacturing technique enabled increased productivity at reduced costs, so much so that by 1912 a Ford model-t could be purchased for $575. During the last half of the 20th Century the introduction of the assem-bly line robot a los increased productivity and further reduced costs, in this article i Will be covering a few important aspects of Mechanical rigging in Blender, then we Will dive into rigging an assembly line robot with an ar-mature for animation. While i wrote this article using Blender 2.5 alpha 2, the same techniques can be used with Blender 2.49b as well, before we dive into this Project, lets cover a few basic i like todo adhere todo for Mechanical rigging. First of, its very important that the root and tip of our armature Bones are positioned exactly at the center of the rotation of the moving parts. If we dont do this the object Will appear todo be falling apart or broken when animating. To accomplish this we Will make extensive use of snapping (shift-s on the keyboard). I a los prefer todo kep all moving parts as sepárate Mesh objects, this Will allow us todo parent the meshes todo the Bones responsible for moving them and avoid the ned for weight painting/vertex groups. And lastly, before starting todo Rig any sort of object we ned todo ensure that the Mesh(es) dont have any scale or rotations todo them. To accomplish this, select the Mesh(es) in object mode and press Control-a, selecting rotation from the pop-up menú. Repeat this step again chosing scale. This ensures that any scale or rota-tion that the Mesh(es) may have acquired during the modeling process is zeroed out. This should always be the first step in the rigging process, failure todo do this step can produce Strange results further down the line.

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As i created each Mesh, y named them todo make it easy todo understand what each part is. So lets go th rouge and look at the diferent parts of the robotic arm. In gray is the base, in green is the turret, in the varying shades of blue are arm1, arm2, and arm3. In red is the hand, in yellow is finger1 and in orange is finger2 (i named the upper fingers topfinger1 and topfinger2, the bottom fingers botfinger1 and botfinger2). Since the base Mesh Will be stationary, this is a god place todo start creating our armature. Select the central bottom vertex of the base Mesh in Edit Mode and use shift-s -> Snap cursor todo selection. Now, in object mode, from the add menú select armature (in 2.5 choose the single bone option) todo create our first bone. Well name this bone base, tab into Edit Mode and bring the tip of the bone todo the top center of the base Mesh, an easy bien todo do this is todo select the base Mesh, enter Edit Mode, select the top center vertex and Snap the cursor todo the selection. Then in the armature Edit Mode, select the tip of the bone and Snap it todo the cursor. Remember, we can hide Mesh objects in object mode with the h-key, and unhide them with alt-h todo better se what we are doing, now, in the armatures Edit Mode, Grab the tip of the bone we just created and extrude (e-key) along the z-axis (z-key). It doesnt matter how much we extrude the bone, as we Will now position the tip by snapping. Select the arm1 Mesh, enter Edit Mode and select the vertex at the center pivot point of this Mesh where it rotates around the turret Mesh. In the armatures Edit Mode, select the tip of the new bone and Snap it todo the cursor.

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Now, since our objects are offset along the x-axis but the main parts form a straight line along the x-axis, we can position the armature todo run straight along the x-axis. The bien we snapped the tip of the new bone has caused this bone todo be angled along the x-axis. To fix this, Snap the cursor todo the root of the new bone, set the pivot center for rotation/scaling todo the 3d cursor, select the tip of the bone and scale along the x-axis by entering 0 on the keyboard, (s-key, x-key, 0-key). The end result should be a perfectly vertical bone when viewed from the front. Dont forget todo name the bone.

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Extrude 2 more Bones along the y-axis using the tech-niques just mentioned for the arm1 and arm2 meshes, extrude the tip, Snap todo pivot point and correct x-axis alignment as neded (if you extrude in the top or side views the x-axis alignment wont be a problem). Repeat for the next bone. Since the hand Will rotate around the center point of the tip of arm3, the bone for this arm segment should run along the center of this Meshs x and z axis. To achieve this, y selected the vértices of arm3 where it Will pivot with arm2, snapped the cursor todo selected and added a bone. The tip of this new bone i snapped todo the center pivot point of the hand/arm3 meshes. Name the bone arm3, and make it an unconnected child of arm2 bone. Extrude the tip of arm3 bone along the y-axis (e-key, y-key) a bit todo make the hand bone.

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On todo the fingers. This part was a bit tedious. To make it easier i hid (h-key) the hand and arm3 meshes so i could really zoom in on the finger meshes and concéntrate on them. First, y selected the topfinger1 Mesh, entered Edit Mode, selected the outside two rings of the Mesh and snapped the cursor todo selection. With the cursor positioned, enter the armatures Edit Mode and add a bone (shift-a). Now select the topfinger2 Mesh and in Edit Mode select the outside two rings, Snap the cursor todo selection. Select the newly created bones tip and Snap selection todo cursor. The new bone is positioned so its root is at the pivot point of the topfinger1 Mesh and its tip at the pivot point between topfinger1 and topfinger2 meshes, extrude the tip of topfinger1 bone todo make the topfinger2 bone. I extruded mine from the side view and positioned its tip so it was protruding th rouge the topfinger2 Mesh a bit, extruding in side view ensures the Bones Will be aligned along the y-axis correctly. Now repeat this process todo create Bones for the botfinger1 and botfinger2 meshes, the final step here Will be todo make topfinger1 and botfinger1 the children of the hand bone. An easy bien todo do this is select the topfinger1 and botfinger1 Bones in Edit Mode, then select the hand bone, press Control-p and select kep offset from the pop-up menú.

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We ned todo make an adjustment todo these Bones todo en-sure they rotate and move correctly while animating. If you look closely at the Bones, they may not appear todo be perfectly square and aligned with each other, some may appear slightly Twisted. To fix this, we ned todo correct the bone roll angles. I fel this is an often overloked but very important step in the rigging process. To se what we are doing a bit better, in the armature panel under display, turn on axes. This displays the Bones x,y, and z-axes, select all the Bones in Edit Mode and press Control-n, selecting z-axis up from the pop-up menú. This corrects the bones roll angle and aligns them so they all match.

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Ok, so lets test out the rig. Enter postura mode, select a bone and move it around. Now you might be saying todo yourself, hey, the Mesh doesnt move with the Bones and you are correct, the Mesh doesnt move. In order todo get the Mesh todo move with the bone, we Will parent the diferent parts of the Mesh todo the bone that Will control it. In object mode, select the base Mesh, then shift-select the armature, enter postura mode, select the base bone and press Control-p, from the pop-up menú select bone, now the Mesh is parented todo the bone and moving the bone in postura mode Will move the Mesh. Repeat this process for all the meshes and Bones. The final step is todo look down the location, rotation, and scaling of Bones so the Bones cant be posed in a bien that Will make the robot arm appear broken, todo start, open the transform properties window/panel by pressing the n-key from the 3d window. Also, todo bet-ter se what we are doing, enable axes display for the armature in the armature panel. Lets start with the base bone. Select the bone in postura mode and in the transform properties panel, click on all the look icons by the location, rotation, and scale Fields. This Will disable the users ability todo move, rotate, or scale this bone, why did we do this? Because the base of the robot armis stationary and not meant todo move during animation, the armature can be moved around in objectmode todo position it within a scene, but in real life, indus-trial machines like this are anchored todo the flor and never move.

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So lets look at the turret bone. This bone we want todo look down all the location and scale values. Looking closer at the bone, we can se its y-axis is pointing straight up and we do want todo allow it todo rotate on its y-axis, so we Will just look down the x and z-axes for it, pléase note that by default in Blender 2.5 alpha 2 we have 4 rotation Fields, the standard x y, and z, plus an additional field for w, basically the w rotation is for quaternion rotations, but all we really ned todo know now is do not look this one, the arm1 bone we want todo allow todo rotate on its x-axis, so look down everything but the x and w rotations. Repeat this for arm2 and arm3. Now the hand bone we want todo allow rotation on the y axis, so look down eve-rything but the y and w rotations. For topfinger1, topfinger2, botfinger1, and botfinger2 we can look down all location and scale Fields, and look down the y and z rotations, now with all those settings made, no matter what bone is selected and how you attempt todo move it, it Will only move in the bien we allow it todo. This is pretty much a folprof Rig now and no matter how hard anyone tries, they wont be able todo break our robotic arm, unless they change the settings we made.

Conclusión.

I hope everyone had fun and learned something from this tutorial. The robotic arm used in this tutorial can be downloaded from hereand it is rigged as presented, in addition todo writing this article, ive recorded a video demo of the steps presented here, you can view it here, ive a los recorded two other videos on this subject, the first one covers additions todo this Rig resulting in fewer animation controls for easier animation, it can be viewed here. The second video covers tidying up the Rig and creating custom shapes for the controller Bones, it can be sen here. God Luk and happy blending.

Randy blose aquí revolt_randy.

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