Knowledge Base

Article Number: 21 | Post Date: November 17, 2016 | Last Updated: October 6, 2017

## Is it possible to attach a rider to a bicycle or motorcycle? Can I make a pedestrian follow an arbitrary path?

It is now possible to attach a multibody to vehicle objects and create multibody mesh objects in Virtual CRASH 4. Please see Chapter 20 of the User's Guide to learn more (http://www.vcrashusa.com/guide-chapter20/#Multibody).

In Virtual CRASH 3, it is not possible to attach a rider to a bicycle or motorcycle using the current user interface, but continue reading below. In Chapter 14 of the User’s Guide, the process of staging bicycle and motorcycle accidents is explained. Since two-wheeled vehicle systems are inherently unstable, simply placing a multibody object atop a two-wheeled vehicle will cause the vehicle to fall over in short time. One way to counteract this issue is to set up your simulation just prior to the moment of impact, since typically the vertical distance the rider will fall would be very small over a small time interval from time=0 to impact.

Since you will generally want to create an animation which includes some portion of the pre-impact motion, Virtual CRASH 3 allows you to set up a kinematic pre-impact trajectory for your simulated objects. The kinematics tool allows you to propagate your objects through the scene, and once the objects reach the end of their kinematic paths, the physics simulation begins at time = 0. Although the kinematics tool is a reasonable solution to the probably of multibody freefall, it has some limitations; for example, the kinematic path does not use the vehicle dynamics simulation to propagate objects through the scene. This means for an object to follow an arbitrary surface terrain, the user must specify various z positions along the kinematic path.

Though it is not possible to rigidly attach a rider onto a two-wheeled vehicle via the user interface, below we provide custom made models for rider+bicycle and rider+motorcycle systems. In these systems, the riders are fixed to their two-wheeled vehicles. The cg position is moved to z=0 in the local frame to ensure the models remain upright.

These will behave as any other vehicle model, so you can control them using the fast control icons, and you can utilize the auto-driver system. If you intend on using these stable models in an impact simulation sequence, you will need to split up the simulation into two parts: the pre-impact sequence using one of the stable models below, and the impact sequence using the standard vehicle+multibody combination, where the vehicle+multibody combination is carefully placed at the exact same configuration just prior to impact as the stable model. Save the animations for each part, and then merge them together in your favorite 3rd party video editor.

The stable bicycle+rider and motorcycle+rider models are provided below.

## Stable Pedestrian Models

Below we also provide you with male and female runner and male and female walker models that are stabilized by four very small wheels. These are also controlled as any vehicle is controlled, and can be very useful for creating background pedestrians in a busy environment such as a city. You can also use these to guide a pedestrian along a complex path; however, if you intend on simulating a pedestrian impact, you will need to split the sequence into pre-impact and impact segments, where you carefully position the standard multibody model at the position of your stable model just at at the moment of impact. Create two animations, and merge them together in a 3rd party application. Each of the models has very small wheels attached. The track width of each axle can be adjusted if needed for better stabilization.

The stable pedestrian models are provided below.

Tags: Bicycle, motorcycle, riders, bicyclist, motorcyclist, attach rider to bicycle, attach rider to motorcycle, pedestrian following path.