Article Number: 93 | VC6 | VC5 | VC4 | VC3 | Post Date: January 20, 2020 | Updated: November 16, 2024
How can I keep my motorcycle/bicycle and rider upright and at rest before impact?
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Motorcycles and bicycles are two-wheeled systems. With an arbitrary rider + vehicle lateral weight distribution, we expect inherent gravitation instability without a wide base of support to counter gravitationally induced roll-torques. This is why such systems simply fall over when the simulation starts. This can be countered in Virtual CRASH by using either the Kinematics Tool or the Path Animation Tool. This is explained below.
Method 1: Use Kinematics | VC6 | VC5 | VC4 | VC3
If you’re not familiar with the Kinematics tool, we recommend to first read the various posts on the tool here: https://www.vcrashusa.com/vcrash-academy-kinematics-tool
Start your simulation near the moment of impact, with bicycle and rider beginning with an initial speed of 0. This reduces the amount of fall time for the bicycle and rider before impact. Next, select the bicycle and rider and left-click on Create > Physics > Add Kinematics To Selection. You will only need one sequence entry in the sequences menu. Set distance to 0 ft. Because kinematics is used for the bicycle and rider, you must also use it for the bullet vehicle. Assign a kinematics path for the bullet vehicle as you normally would. You should now see the bicycle and rider remain upright until time = 0, followed by a simulated collision.
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Method 2: Use Path Animation | VC6 | VC5 | VC4
If you’re not familiar with the Path Animation tool, we strongly recommend you read the various posts on the tool here: https://www.vcrashusa.com/vcrash-academy-path-animations. In particular, see https://www.vcrashusa.com/blog/2018/6/27/new-possibilities-with-the-path-animation-tool for detailed discussions on complex joint controls of multibodies. It’s also recommended to read: https://www.vcrashusa.com/blog/2018/6/7/building-complex-systems-with-joint-tools to better understand joint tools.
In our example, rather than using kinematics, we can also simply attach the bicycle to a forward evaluate animation path. Only a “reaction” sequence entry is used here. The time input value is set such that the “off” sequence entry, which releases the bicycle from animation path control to simulation control, occurs just prior to impact. A multibody, which is converted to a rigid body object, is placed on the bicycle and held in place by 3 spherical joints. The joint connections are made to break just prior to impact. The multibody’s joint stiffness values are set to large values, then to 0 just prior to impact by using the rectangular pulse option. The bullet vehicle is simply simulated from pre-impact to post-impact as usual.
The video below walks the view through the workflow of attaching a multibody to a bicycle which is controlled by an animation path.
Method 3: Linking | VC6 | VC5
If you don’t need your rider to a independent simulated object, but instead simply want a representation of a rider on bicycle or motorcycle (or driver in a car or truck), in may be preferrable to follow the steps below.
(1) Create a multibody, pose, and position on or inside of vehicle as needed (see Guides (VC6 | VC5 | VC4 | VC3)).
(2) Convert multibody to mesh using tools > convert > “to mesh”. This will “freeze” the multibody into the desired pose. Recall, this pose cannot be changed after “to mesh” is used. The mesh is converted to a passive object (non-rigid body), and therefore will not interact with other objects via physics.
(3) Go to the converted multibody’s mesh menu. Left-click on “Link.” Next, hover the mouse over the vehicle (it will change to a light blue color), then left-click on the vehicle. This will link the multibody to the vehicle, such that as the vehicle moves through your scene, the linked object will move in the exact same manner. Linked objects can be freely translated and rotated with respect to the parent to which they are linked at any time after the linking process is completed. Note, neither the multibody nor the vehicle or object to which the multibody is to be linked can be frozen when trying to use the link feature.
Remember, linked objects do not participate in physics interactions and are complete passive.
Tags: motorcycle, bicycle, upright, stability, bicycle falls over, falling over.
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