Home » Featured, JScript, XSI

Building A Car Rig

5 January 2012 131,970 views 2 Comments

Back to previous page.

Stage Two: Setting up suspension dynamics

  1. Press [9] for schematic view. Select the yellow object called GroundDetect. Go to Model > Modify > Deform > Shrinkwrap and pick the black object called Ground, then right click. Set Projection to "Parallel to Axes", Reference to "Deformed object", and enable the Along Y checkbox. Enable Show > Operator Links in the schematic view and disable Show > Links On Selected Nodes Only to see the new connection.

  2. Now that we’ve set up the wheel / ground collision detection, we’ll set up the suspension simulation. Select the black Suspension_Base object and go to Simulate > Create > Rigid Body > Passive Rigid Body. Now select the Suspension_Top object and go to Simulate > Create > Rigid Body > Active Rigid Body.

  3. Select the Suspension_Base object and go to Simulate > Create > Rigid Body > Rigid Constraint > Slider, then pick Suspension_Top. In the slider parameters, set the Spring to 80, Damping to 6 and Rest Length to 9. To place the slider into the wheel rig hierarchy, select the Wheel_Base object, click on the Parent button, and then select the slider with left mouse button and right click.


Tech Tip

Due to inaccuracies in the simulation, the top of each suspension arm will tend to wobble from side to side. To avoid this, we use an extra object called Body_Attach which we constrain to follow only the vertical movement of the suspension arms (see following steps). It is possible to reduce inaccuracies by increasing the number of sub-steps performed in the simulation. To do this, close all open windows and go to Simulate > Modify > Rigid Body > Edit Simulation Properties. Increasing the Substeps parameter will improve accuracy at the expense of performance, and you will find that you have to set this to a very high value to eliminate wobble altogether. Around 30 is a good value.

  1. In the schematic view, select the Body_Attach object. From the main control panel on the right hand side of the screen press the Selection button to examine its contents. Click on the icon of the Local Transform entry to open a property page (PPG) of its settings.

  2. Right click on the green divot of the Position Y parameter, and select Set Expression from the popup menu. In the expression editor, type "this_model.Suspension_Top.kine.local.posy" (no quotes) and press Apply. This will match the Body_Attach object to the height of the suspension. Since we have used the keyword "this_model" in the expression, it will automatically work for the other wheel rigs.


Move on to the next page to continue.

1 Star2 Stars3 Stars4 Stars5 Stars (3 votes, average: 5.00 out of 5)


  • Bubba said:


  • Francesco said:

    XSI 9.5?

    Thanks for this tutorial