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Robotiq 2F 85 gripper
For this gripper, the following Github repo can be used as a reference: https://github.com/Shreeyak/robotiq.git
mimic tag in URDF
This gripper is developed for ROS and uses the mimic
tag within the URDF files to make the gripper move. From our research mimic
tag within URDF is not supported by pybullet. To overcome this, one can use the createConstraint
function. Please refer to this example from the bullet3 repo to see how to replicate a mimic
joint:
#a mimic joint can act as a gear between two joints
#you can control the gear ratio in magnitude and sign (>0 reverses direction)
import pybullet as p
import time
p.connect(p.GUI)
p.loadURDF("plane.urdf",0,0,-2)
wheelA = p.loadURDF("differential/diff_ring.urdf",[0,0,0])
for i in range(p.getNumJoints(wheelA)):
print(p.getJointInfo(wheelA,i))
p.setJointMotorControl2(wheelA,i,p.VELOCITY_CONTROL,targetVelocity=0,force=0)
c = p.createConstraint(wheelA,1,wheelA,3,jointType=p.JOINT_GEAR,jointAxis =[0,1,0],parentFramePosition=[0,0,0],childFramePosition=[0,0,0])
p.changeConstraint(c,gearRatio=1, maxForce=10000)
c = p.createConstraint(wheelA,2,wheelA,4,jointType=p.JOINT_GEAR,jointAxis =[0,1,0],parentFramePosition=[0,0,0],childFramePosition=[0,0,0])
p.changeConstraint(c,gearRatio=-1, maxForce=10000)
c = p.createConstraint(wheelA,1,wheelA,4,jointType=p.JOINT_GEAR,jointAxis =[0,1,0],parentFramePosition=[0,0,0],childFramePosition=[0,0,0])
p.changeConstraint(c,gearRatio=-1, maxForce=10000)
p.setRealTimeSimulation(1)
while(1):
p.setGravity(0,0,-10)
time.sleep(0.01)
#p.removeConstraint(c)
Details on createConstraint
can be found in the pybullet getting started guide.
Files in folder
Since parameters like gear ratio and direction are required, one can find the robotiq_2f_85_mimic_joints.urdf
which contains the mimic tags as in original URDF, which can be used as a reference. It was generated from robotiq/robotiq_2f_robot/robot/simple_rq2f85_pybullet.urdf.xacro
as so:
rosrun xacro xacro --inorder simple_rq2f85_pybullet.urdf.xacro
adaptive_transmission:="true" > robotiq_2f_85_mimic_joints.urdf
The URDF meant for use in pybullet is robotiq_2f_85.urdf
and it is generated in a similar manner as above by running:
rosrun xacro xacro --inorder simple_rq2f85_pybullet.urdf.xacro > robotiq_2f_85.urdf