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Building A Car Rig

5 January 2012 105,543 views 2 Comments

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Stage Three: Constructing the main rig

Tech Tip

Always try to have your rig and 3D mesh as separate models. You can link them by constraints later. In production, this is an essential technique for separating workflow inside a large team. It means that modelling, rigging, and animation can be worked on independently, and it’s easier to make changes later. Another great tip is to realise that the schematic view is a rigger’s best friend. When constructing complex rigs, it is an extremely helpful tool for visualising how your rig is organised. For all the steps in this tutorial, I strongly recommend that you have this view open, as many of the steps are written with that in mind.

  1. First, we need to connect the wheel rig to the ground detection system. In the schematic view, select the orange Wheel_Base object and go to Constrain > Surface (param), then pick the yellow Ground_Detect object. In the parameter page for the newly created constraint, set the U Location of the constraint to one and leave the V Location at zero. You can ignore the Tangent and Normal tabs.

  2. Middle click on the WheelFL model and press [CTRL]+[d] three times. In the schematic view, press [CTRL]+[r] to rearrange the objects. Note that you can press [m] to rearrange nodes manually. Using the middle mouse button will move a whole hierarchy at once. Rename the new models WheelFL1, WheelFL2, WheelFL3 to WheelFR, WheelBL, and WheelBR. Access the name by double clicking the node, or by selecting and pressing [Enter].

  3. In the schematic view, find the Wheel_Base object under the WheelFR model, drag select over its Surface constraint. Press [Enter] to edit the settings of the selected constraint and set the U Location to zero. This will move the front right wheel rig to its correct location. Similarly for WheelBL, set U to one and V to one, and for WheelBR set U to zero and V to one.

  4. From the main control panel, enable snapping by pressing the ON button under snap. Right click on the first snap type icon (which looks like a dot) and enable just the "center" option. In the main viewport press [n] and click at the top of each suspension arm to create a single rectangular polygon between the tops of the wheel rigs (see screen shot). Press [Space] to finish.

  5. With the new polygon object selected, press [Enter] and rename it to SuspensionLink. Turn snapping off. We now need to link this new object to the suspension. Before proceeding, verify that each wheel rig is in the correct location. For example, middle click WheelFL to highlight it in the viewport and make sure that it is at the front left (FL) of your rig.

  6. Make sure the SuspensionLink object is selected. Press [t] to enter point selection mode. Select the front left point of the mesh. Go to Model > Deform > Cluster Center, and then select the Body_Attach object under the WheelFL model. Select the front right point and do the same for the Body_Attach object under WheelFR. Do the same for the back left (BL) and back right (BR) points.

  7. The SuspensionLink object is what drives the rolling motion of the body as the suspension reacts to the ground. Each point on the SuspensionLink object should now be constrained to its own Body_Attach object. To move this object into the car rig hierarchy, select the CarRig model, click on the Parent button, and then select the SuspensionLink with left mouse button and right click.

  8. This is a good time to check our work, but save a copy of the scene first. In the playback control, set your scene frame range to something large like 10000 and press play. If you move the PathFollower in the XZ plane over the bumpy terrain, the suspension should bounce nicely in response. If the suspension goes out of alignment, read the following tip to fix it.


Tech Tip

Note that the start scene had already set key frames on local position and rotation for the suspension rigid objects to define their initial state. This makes it easier to adjust the rig when setting up shots. If at any stage the Suspension_Top objects become incorrectly positioned, select them and go to Simulate > Modify > Rigid Body > Use Animation As Initial State. This will reset their positions. To locate these rigid bodies quickly, open XSI Explorer (press [8]), switch to "Environments" view, and expand the group called "RigidBodies". Alternatively, you can temporarily disable the simulation by going to Simulate > Modify > Rigid Body > Edit Simulation Properties, and turning off the Active flag.

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  • Bubba said:


  • Francesco said:

    XSI 9.5?

    Thanks for this tutorial