Blender Beginner for Beginner Tutorial: Mech Model Part 3: Rigging

20th June 2010 – Blender 2.47

After creating and texturing a mech model, the next step towards animating it is rigging. This is the process of setting up bones in the model such that when the bone is moved, the mech mesh deforms in an expected manner. The final set of bones to animate a walk cycle is shown in the image below. Once this step is complete, the model will be ready to animate.

Mech


  1. Before starting ensure the mech is positioned such that it straddles the X-axis – place a leg on each side of the origin with the average X location of the whole mech set to 0 (assuming the mech is symmetrical). This is so that some mirroring functions of rigging, which work only in the X-axis, can be applied.
  2. Go to a side view (NUMPAD3). Start by removing any transformations, (there shouldn’t be any, but just in case we don’t want them interfering with the bones). With the mech model selected in Object mode press CTRL-A and choose to set Scale and Rotation to ObData (as a result the model’s Rot values should go to 0 and the Scale values to 1 – look at the Transform Properties with the N KEY). Now add the armature (SPACE → Add → Armature). A little double-headed pyramid object will appear – this is the master bone, other bones will be connected to it such that when the master bone moves all other bones move the same way. Use the G KEY to position it behind the hips of the mech. Also the tip (narrow bit of the bone) should be facing away from the mech, while the root (thicker part of the bone) should be nearer the mech. The bone can be stretched or angled by selecting it in Object mode and then going to Editing mode (TAB) then grabbing the tip to move it – just like other objects. On the Armature subpanel of the Editing (F9) panel set Names on (so the names of the bones are shown on screen) and X-Ray on (so the bones can be seen through the model). With the bone in Edit mode change its name from the default Bone to Master, this is done on the Transform Properties box on bone. Also, disable the transformation manipulator, so the screen is less cluttered (CTRL-SPACE → Disable).
  3. Next the leg bones. Set X-Axis Mirror on the Armature subpanel (this is why the mech was positioned across the x-axis). Select the root of the master bone in edit mode and then press SHIFT-E. This will extrude two bones out from the master bone, although only one can be seen at the moment. The master bone will be the parent of these new bones . The parent relationship means that the bones move with each other. Move the end of the extruded bone to the centre of the knee.
  4. Go to front view (NUMPAD1) and grab one of the extruded bones. As you move it you will see another mirrored bone. One will be named Master_L and one Master_R, for left and right. Whichever you have grabbed, move it to the appropriate leg so that the root is in the centre of the hip and the tip in the centre of the knee. Shift back and forth between side and front views, moving the bone until it is properly positioned inside the upper leg of the mech (roughly positioned is good enough, pinpoint accuracy is not required). By positioning one of the bones, the other should also be in the correct position thanks to the X-Axis Mirroring. Then rename them Upper_Leg_L and Upper_Leg_R.
  5. Select the tip of one of the upper leg bones and press SHIFT-E again. Two more bones are extruded this time with their roots attached to the tip of the upper leg bones. Because we extruded from the tip rather than the root this means this bone is a connected child of the upper leg bone (extruding from the root makes the child bone unconnected). Move them so that they go from the knee to the foot (again switching views). Rename them Lower_Leg_L and Lower_Leg_R.
  6. Next create the ankle by selecting the tip of lower leg and CTRL_RMB click behind the base of the leg (this works like extrude, the resulting bone is a child of the first bone). Position the ankles so that they extrude horizontally from the tip of the lower legs. Rename them as ankles and remove their parent bone by blanking the “child of” box on the Armature Bones subpanel when the bone is selected. It might help to change from viewing the bones as octahedrons to sticks, as the former will fill up too much of the screen for the fine detail work to come.
  7. Create the feet by selecting the tip of the lower leg again and CTRL_RMB click in the centre of foot. Position them and rename them as feet. The feet should be children of the ankles – select one of the feet then SHIFT select the appropriate ankle, press CTRL-P to create the parent relationship (select Keep Offset). This wasn’t done by extruding from the ankle so that everything is in the right position.
  8. Make the toes children of the feet. They should not be connected to the feet and should be positioned at the edge of the mesh’s toes so the toes won’t roll strangely as the side toes are off-axis compared to the of the rest of the legs.
  9. Select all bones (press A KEY until all bones are selected). Press CTRL-N and accept the option presented – this will remove any roll applied to the bone and will make predicting the way they move easier. Next the legs should act as a chain, so moving the lower leg moves the upper leg too. This is called an IK chain. The ankles will be the controllers for the legs – moving them will move the entire leg. Go to Pose mode (CTRL-TAB until the mode selector says Pose, or just select it from the dropdown), select the ankle and SHIFT select the lower leg. Press CTRL-I and accept the To Active Bone option. This makes the ankle the target bone of the IK chain bones in the legs. IK means Blender will move the chain bones (lower leg) to keep the end bones (upper leg) in place despite movement of the target (ankles). The IK target can’t be a child of one of the bones in the chain (this causes a cyclic dependency), so this is why the ankles are not children of the lower legs. Try grabbing the ankle (you know which one is selected as it will be highlighted in blue) and moving or rotating it to see how the IK chain works, but make sure you return it to the original location when done.
  10. The toes should only be able to move up or down, not from side to side. To prevent this, click the little lock icon next to the Loc values and Rot values on the Transform Properties panel, except for the LocZ value.
  11. To make the ankles move with the mech as a whole, set them to have the master bone as their parent, keeping the offset.
  12. Now the legs are setup, bones for the body are required so that it too will move with the mech. Create a bone for the spine running from the hips up to the top of the body, with the master bone as its parent. Create another bone as a child of the spine, which runs along the body horizontally (or nearly so). Create a bone running along the hips as a child of the spine.

    Make the upper legs children of the hips. Since we don’t want the IK chain to affect the hips, the length of the chain needs to be set to 2, so it just affects the lower and upper legs (2 being the number of bones in the chain). By default an IK chain will affect all the bones up a chain. With one of the leg bones selected in Pose mode, set the ChainLen value to 2 on the IK constraints config on the Constraints subpanel.

  13. So far when the bones are moved the mech mesh does not move too. With the armature complete we can make it deform the mech. Go to Object mode and select the whole armature, then SHIFT select the mech model and press CTRL-P, selecting Object from the options displayed. With the mech selected in Object mode, go to the Modifiers subpanel of the Editing panel. Click Add Modifier and choose Armature from the available options. Deselect the Vert Group option on the new modifier’s config and enter the name of the armature (probably “Armature”) in the Ob field.
  14. Select the armature and go into Pose mode. Select an ankle and try moving it. The mech mesh underneath moves as well. Unfortunately, you will probably find too much of the mesh moves. This is because each bone is affecting too much of the mesh. In the image below you will see that when a leg is moved, some of the body and toes also move in a strange way.

    The parts of the mesh affected by each bone need to be changed. This can be done in in pose mode, turn on Envelope option on the Armature subpanel (the shaded bit around the bone shows the area of influence of the bone), select a bone and then use ALT-S to change the size of the envelope. This doesn’t work for this mesh – there is too much fine detail and the mesh vertices need to be assigned individually to bones. To do this, turn off Envelopes on the mesh’s Armature constraint on the Modifier subpanel and turn on Vert Groups. Select the armature, enter Pose mode, and select the all bones. Select the mech model and enter Weight Paint mode (CTRL-TAB until the mode selector displays Weight Paint), press W and confirm “Apply Bones Envelopes to Vertex Groups”. Now Blender is using vertex groups rather than envelopes to determine what is affected, and you have converted the previous envelopes to vertex groups. Selecting a bone now will show a weight map of what is affected by that bone. The below image shows the vertices affected by the upper leg.

    Red represents those parts of the mesh greatly affected by the selected bone, blue shows those parts not affected. So you can see above that moving the upper leg will also affect part of the body (the non-blue bit). The Weight Paint mode allows “painting” on the model to choose which vertices are affected by the selected bone. The Paint subpanel on the Editing panel allows control of the painting. Turn on the All Face, Wire and Soft options. The Sub option will remove vertices, so use this with the upper leg selected and remove any non-blue vertices other than the upper leg and knee. Do the same on the other side. It should look like the below.
    Do the same with all the bones using Sub or Add, with various brush sizes to have the bones affect the mesh as you expect (to get back to Paint mode from Pose mode perform the same process of selecting all the bones in Pose mode, then selecting the mesh, then going to Weight Paint mode – although don’t press W after the first time).

And it is done. Try moving the mech around using the master, spine and ankle bones – this should provide all the movement required. You can download the blend file here. The next stage is to animate a walk cycle

Creative Commons License
Mech Rigged Blender Model by Charles Cordingley is licensed under a Creative Commons Attribution 2.0 UK: England & Wales License.