Keywords: symbolic, multibody, recursive, contact, real-time.

In this paper we use recently developed state of the art symbolic multibody methods for the development of an accurate multibody model of a locomotive. This is a complex multibody model with 21 bodies and 8 contact points (one per wheel). The model is generated through the direct application of the virtual power principle, with contact forces modeled using the standard linear Kalker model, and contact enforced through constraint equations. No simplifications as order or base parameter reduction, partial-linearization or precalculated tables for contact kinematics are used.

In order to show the performance of our approach an implicit trapezoidal rule is used for the direct numerical simulation of the locomotive. The method of independent coordinates is used for the direct solution of the dynamic and constraint projection equations. The time required for the evaluation of the model functions including the Kalker model is less than or approximately 1ms, with a stable 1ms time step used in the integration. Soft real-time performance can therefore beachieved with this time step, although hard real-time performance is not achieved because for a relatively small number of time steps the simulation can be three times slower than real-time.

It should be noted that no special optimizations are introduced in the equation solution procedures nor in the integrator implementation. That's why it suggested in this paper that there is room to greatly improve these results just using some well known techniques for the solution of the dynamics and projection equations generated.

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