Building the RoKi Plugin¶

Installing RoKi ¶

To use the RoKi Plugin, you need to install RoKi (Robot Kinetics library) beforehand. RoKi is only supported on Linux.

First, install CURE.

Navigate to the CURE page from the RoKi homepage, download cure-1.0.0-beta5.tgz and extract it.

There is a file called README, so basically follow the instructions in it for installation.

Note

The default installation destination is home/usr. The following explanation is for installing to this location. If you want to change the installation destination, edit the config file and modify the following content accordingly.

It seems better to create the installation destination folder in advance, and also create bin and lib folders within it. Start a terminal and in the home directory, do the following:

mkdir usr
cd usr
mkdir bin
mkdir lib

Add this directory to the environment variables PATH and LD_LIBRARY_PATH. Open the .profile file in the home directory with an editor. Paste the following content at the end of the file and save it.

export PATH=$PATH:$HOME/usr/bin
export LD_LIBRARY_PATH=$HOME/usr/lib:$LD_LIBRARY_PATH

To apply this setting, execute:

source .profile

Move to the directory where you extracted the Cure source and execute the following:

make
make install

If successful, a file called cure-config should be created under home/usr/bin, and libcure.so should be created under home/usr/lib.

Next, navigate to the ZM page, download the file, and extract it. Move to the extracted directory and perform make, make install.

Install Zeo and Roki in the same manner in that order.

Building the Plugin ¶

When building choreonoid, set the BUILD_ROKI_PLUGIN item to “ON” in the CMake configuration, and specify the RoKi installation destination in ROKI_DIR.

Running Simulations ¶

Simulations using the RoKi Plugin are performed in the same way as using other physics simulators. You can execute simulations by creating a simulator item “RoKiSimulator” and placing it as a child item of the world item.

Properties of RoKiSimulator Item ¶

The RoKiSimulator item has the following properties.

RoKi Plugin Properties¶
Property	Description
staticfriction	Static friction
kineticfriction	Kinetic friction
contactType	Type when objects contact: select rigid or elastic
solverType	Select Vert or Volume
compensation	Contact parameter, effective when contactType is rigid and useContactFile is false
relaxation	Contact parameter, effective when contactType is rigid and useContactFile is false
elasticity	Contact parameter, effective when contactType is elastic and useContactFile is false
viscosity	Contact parameter, effective when contactType is elastic and useContactFile is false
useContactFile	Whether to load contact parameter settings from a file
contactFileName	Contact parameter setting file name, effective when useContactFile is true

For details about the parameters, please refer to the RoKi homepage.

Joint Dynamics Simulation ¶

RoKi enables joint dynamics simulation. The sample project for this is RokiArm2Dof.cnoid.

The joint dynamics parameters are described in the model file arm_2dof.body. Since this model applies the same parameters to two joints, it uses import in the Link Node. For information about the alias feature, see Using Aliases. When setting different parameters for each joint, write them directly in the Link node.

actuator1: &actuator1
  rotorInertia: 1.65e-6
  gearRatio: 120.0
  gearInertia: 5.38e-6
  motorAdmittance: 0.42373
  motorConstant: 2.58e-2
  motorMinVoltage: -24.0
  motorMaxVoltage: 24.0
  jointStiffness: 0.0
  jointViscosity: 2.2
  jointFriction: 4.32
  jointStaticFriction: 4.92

links:
   .......
  -
    name: Joint1
     .......
    import: *actuator1
     .......
  -
    name: Joint2
     .......
    import: *actuator1
     .......

The joint parameters are as follows.

Parameter	Description
motorconstant	Motor constant (torque constant)
admitance	Terminal admittance (reciprocal of terminal resistance)
minvoltage	Minimum input voltage
maxvoltage	Maximum input voltage
inertia	Motor rotor moment of inertia
gearinertia	Gear reducer moment of inertia
ratio	Reduction ratio
stiff	Joint stiffness coefficient
viscos	Joint viscosity coefficient
coulomb	Joint dry coefficient (kinetic friction torque)
staticfriction	Maximum static friction torque

Fracture Simulation ¶

RoKi enables fracture simulation by describing the locations where fractures occur as joints in the model file. The sample project for this is RokiBreakWall.cnoid.

The fracturing model is described in breakWall.body. Define the locations where fractures occur as joints, and set the joint type to free. Then, describe the force and torque norm thresholds at which fractures occur in the break parameter, in the order of force and torque.

links :
  -
   name: BASE
   jointType: fixed
    ................
   elements:
     Shape:
       geometry: { type: Box, size: [ 0.099, 0.049, 0.099 ] }
  -
   name: link1
   parent: BASE
   translation : [ 0, 0, 0.05 ]
   jointType: free
     .............
   break: [ 200.0, 200.0 ]
     .............
   elements:
     Shape:
       geometry: { type: Box, size: [ 0.099, 0.049, 0.099 ] }
 -
   name: link2
   parent: link1
   translation : [ 0, 0, 0.1 ]
   jointType: free
     .............
   break: [ 10.0, 10.0 ]
     .............

To prevent the fractured objects from passing through each other, the self-collision detection property of the breakWall model item must be set to true. However, this would cause self-collision even before fracturing. To avoid this, the breakWall model sets the geometric shapes of the links so that there are slight gaps between the links.

Set the all link position and orientation output property of the RoKiSimulation item to true.

Building the RoKi Plugin¶

Installing RoKi¶

Building the Plugin¶

Running Simulations¶

Properties of RoKiSimulator Item¶

Joint Dynamics Simulation¶

Fracture Simulation¶