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Building A Car Rig

5 January 2012 131,976 views 2 Comments

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Stage Seven: Animation and Automatic Steering

Tech Tip

If you have a lot of objects loaded, the schematic view can get overrun with objects. There are ways to cope with this. Firstly, you can select a parent node in the schematic view and press [n]. This will collapse all child objects into the selected node. Press [n] to expand the nodes again when you need to. This way, you can make sure you only view objects that you want. You can also turn on Show > Links on Selected Nodes Only which helps to hide much of the clutter. Finally, you can distribute objects between different layers by pressing [6] to open the layer dialog. You can then view just the current layer in the schematic view by pressing [y].

  1. Select the PathFollower object, and go to Constrain > Curve (Path), then select the VehiclePath NURBS curve. On the constraint’s Path Percentage parameter, set a keyframe at frame one with a value of zero. This is the animation curve that you can use to animate the motion of the Hummer. Go to the Tangency tab and enable the Active switch. Press the Z button to align the vehicle correctly.

  2. Create a new null object by going to Model > Primitive > Null and parent it under the PathFollower object. Rename it to SteerControl. Constrain it to the path by going to Constrain > Curve (Path). Enable just Tangency and press the Z button for this new constraint. Set the following expression on the Path Percentage parameter: "this_model.PathFollower.kine.pathcns.perc + 4"

  3. To make the wheels steer in the correct direction, select the Wheel_Steer object under the WheelFL model (it looks like a green arrow in the viewport). Open the Local Transform property. Set the following expression on the Y Rotation parameter: "CarRig.SteerControl.kine.local.roty". Repeat these steps for the WheelFR model.

  4. Turn on 3D objects again and animate the Path Percentage parameter of the constraint on the PathFollower object. To access it, select the PathFollower object and press the Selection button on the main control panel. Expand the Constraints folder and click on the icon of the PathCns item. To add body roll, you will need to animate the local Z rotation of the CarHandle object. For added realism, you can also animate the parameters of the wheel turn operators to add skidding and wheel spin. To find the wheel turn operators, select the appropriate Wheel_Rot object and press the Selection button on the main control panel. Expand the tree underneath Local Transform until you see the WheelTurnOp entry. Click the S shaped icon to edit it.

    Don’t forget to check out the vehiclerig_final scene file for an example animation.


So that’s it! Congratulations if you managed to work your way through all those steps. Please let me know in the comments below if you find any problems with any of the steps, or if you just need clarification.

Thanks for reading,

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  • Bubba said:


  • Francesco said:

    XSI 9.5?

    Thanks for this tutorial