.. _agxModel_twobodytire:

===============
AGX Model: Tire
===============

**agxModel::TwoBodyTireModel** is an implementation of a tire model with two separate rigid bodies; the tire and the rim. The user has control over the deformation of the different degrees of freedom by setting stiffness and damping:


.. image:: images/agxmodel_1.png


Creating a TwoBodyTireModel requires two bodies, one for the rim and one for the rigid body. It is assumed that the two bodies are positioned and added to the simulation before or after the creation of the TwoBodyTireModel

.. code-block:: c++

  agx::Real tireRadius = 1;  // Not important, but can give information of
  agx::Real rimRadius = 0.5; // amount of deformation of tire.
  agx::Real stiffness = 2E6;

  agxModel::TwoBodyTireModelRef tire =
  	new agxModel::TwoBodyTireModel(tireBody, tireRadius, rimBody, rimRadius );


^^^^^^^^^
Stiffness
^^^^^^^^^

The stiffness of the tire will control the amount of deformation for the tire. There are four degrees of freedom for which the stiffness can be specified.

The unit for translational stiffness is **force/displacement** (if using SI: N/m). The unit for rotational stiffness is **torque/angular displacement** (if using SI: Nm/rad)

.. code-block:: c++

  // Configure the deformation stiffness for all DOF of the tire
  tire->setStiffness(stiffness*2, agxModel::TwoBodyTire::RADIAL)
  tire->setStiffness(stiffness*10, agxModel::TwoBodyTire::LATERAL)
  tire->setStiffness(stiffness*4, agxModel::TwoBodyTire::BENDING)
  tire->setStiffness(stiffness*0.1, agxModel::TwoBodyTire::TORSIONAL)


^^^^^^^
Damping
^^^^^^^

The damping corresponds to the rate of which the deformation should be restored. It has the same degrees of freedom as the stiffness.

The unit for translational damping is **force * time/displacement** (if using SI: Ns/m). The unit for the rotational damping coefficient is **torque * time/angular displacement** (if using SI: Nms/rad)

.. code-block:: python

  dampingCoefficient = 70000

  tire.setDamping(dampingCoefficient*2, agxModel.TwoBodyTire.RADIAL)
  tire.setDamping(stiffness*10, agxModel.TwoBodyTire.LATERAL)
  tire.setDamping(stiffness*4, agxModel.TwoBodyTire.BENDING)
  tire.setDamping(stiffness*0.1, agxModel.TwoBodyTire.TORSIONAL)