Modifying the Model in Code

RaiSim allows users to modify most of the robot parameters freely in code. This allows users to create randomized robot models, which might be useful for AI applications (i.e., dynamic randomization). Note that a random model might be kinematically and dynamically unrealistic. For example, joints can be locked by collision bodies. In such cases, simulation cannot be performed reliably and it is advised to carefully check randomly generated robot models.

Here is a list of modifiable kinematic/dynamic parameters.

  • Joint Position (relative to the parent joint) Expressed in the Parent Frame

getJointPos_P method returns (a non-const reference to) a std::vector of position vectors from the parent joint to the child joint expressed in the respective parent joint frames. This should be changed with care since it can result in unrealistic collision geometry. This method does not change the position of the end-effector with respect to its parent as the position of the last link is defined by the collision body position, not by the joint position. The elements are ordered by the joint indices.

  • Joint Axis in the Parent Frame

getJointAxis_P method returns (a non-const reference to) a std::vector of joint axes expressed in the respective parent joint frame. This method should also be changed with care. The elements are ordered by the joint indices.

  • Mass of the Links

getMass method returns (a non-const reference to) a std::vector of link masses. IMPORTANT! You must call updateMassInfo() after changing mass values. The elements are ordered by the body indices (which is the same as the joint indices in RaiSim).

  • Center of Mass Position

getBodyCOM_B method returns (a non-const reference to) a std::vector of the COM of the bodies. The elements are ordered by the body indices.

  • Link Inertia

getInertia method returns (a non-const reference to) a std::vector of link inertia. The elements are ordered by the body indices.

  • Collision Bodies

getCollisionBodies method returns (a non-const reference to) a raisim::CollisionSet, a std::vector of raisim::CollisionDefinition. This vector contains all collision bodies associated with the articulated system.

getCollisionBody method returns a specific collision body instead. All collision bodies are named “LINK_NAME” + “/INDEX”. For example, the 2nd collision body of a link named “FOOT” is named “FOOT/1” (1 because the index starts from 0).

A CollisionDefinition holds the position and orientation offset from the body frame (posOffset, rotOffset), the body index (localIdx), the shape and its parameters, and the collision body handle (getCollisionBody()). To change the shape or the offsets of a collision body, use setCollisionBodyShapeParameters() (primitive shapes only), setCollisionBodyPositionOffset() and setCollisionBodyOrientationOffset() of the articulated system with the index of the collision body in getCollisionBodies(). Users can also change the material of a collision body with setMaterial(), which affects the contact dynamics, and its collision group and mask with setCollisionGroup() and setCollisionMask().

Collision

Apart from the collision mask and collision group, users can also disable a collision between a certain pair of bodies with ignoreCollisionBetween(bodyIdx1, bodyIdx2). If the system is already in a world, call updateSelfCollisionCache(world) afterwards.