test.py

import pybullet as p
import pybullet_data

def getJointStates(robot):
  joint_states = p.getJointStates(robot, range(p.getNumJoints(robot)))
  joint_positions = [state[0] for state in joint_states]
  joint_velocities = [state[1] for state in joint_states]
  joint_torques = [state[3] for state in joint_states]
  return joint_positions, joint_velocities, joint_torques


def getMotorJointStates(robot):
  joint_states = p.getJointStates(robot, range(p.getNumJoints(robot)))
  joint_infos = [p.getJointInfo(robot, i) for i in range(p.getNumJoints(robot))]
  joint_states = [j for j, i in zip(joint_states, joint_infos) if i[3] > -1]
  joint_positions = [state[0] for state in joint_states]
  joint_velocities = [state[1] for state in joint_states]
  joint_torques = [state[3] for state in joint_states]
  return joint_positions, joint_velocities, joint_torques


def setJointPosition(robot, position, kp=1.0, kv=0.3):
  num_joints = p.getNumJoints(robot)
  zero_vec = [0.0] * num_joints
  if len(position) == num_joints:
    p.setJointMotorControlArray(robot,
                                range(num_joints),
                                p.POSITION_CONTROL,
                                targetPositions=position,
                                targetVelocities=zero_vec,
                                positionGains=[kp] * num_joints,
                                velocityGains=[kv] * num_joints)
  else:
    print("Not setting torque. "
          "Expected torque vector of "
          "length {}, got {}".format(num_joints, len(torque)))


def multiplyJacobian(robot, jacobian, vector):
  result = [0.0, 0.0, 0.0]
  i = 0
  for c in range(len(vector)):
    if p.getJointInfo(robot, c)[3] > -1:
      for r in range(3):
        result[r] += jacobian[r][i] * vector[c]
      i += 1
  return result


clid = p.connect(p.SHARED_MEMORY)
if (clid < 0):
  p.connect(p.DIRECT)

time_step = 0.001
gravity_constant = -9.81
p.resetSimulation()
p.setTimeStep(time_step)
p.setGravity(0.0, 0.0, gravity_constant)

p.loadURDF("plane.urdf")

kukaId = p.loadURDF("TwoJointRobot_w_fixedJoints.urdf", useFixedBase=True)

p.resetBasePositionAndOrientation(kukaId, [0, 0, 0], [0, 0, 0, 1])
numJoints = p.getNumJoints(kukaId)
kukaEndEffectorIndex = numJoints - 1

# Set a joint target for the position control and step the sim.
setJointPosition(kukaId, [0.1] * numJoints)
p.stepSimulation()

# Get the joint and link state directly from Bullet.
pos, vel, torq = getJointStates(kukaId)
mpos, mvel, mtorq = getMotorJointStates(kukaId)

result = p.getLinkState(kukaId,
                        kukaEndEffectorIndex,
                        computeLinkVelocity=1,
                        computeForwardKinematics=1)
link_trn, link_rot, com_trn, com_rot, frame_pos, frame_rot, link_vt, link_vr = result
# Get the Jacobians for the CoM of the end-effector link.
# Note that in this example com_rot = identity, and we would need to use com_rot.T * com_trn.
# The localPosition is always defined in terms of the link frame coordinates.

zero_vec = [0.0] * len(mpos)
jac_t, jac_r = p.calculateJacobian(kukaId, kukaEndEffectorIndex, com_trn, mpos, zero_vec, zero_vec)

print("Link linear velocity of CoM from getLinkState:")
print(link_vt)
print("Link linear velocity of CoM from linearJacobian * q_dot:")
print(multiplyJacobian(kukaId, jac_t, vel))
print("Link angular velocity of CoM from getLinkState:")
print(link_vr)
print("Link angular velocity of CoM from angularJacobian * q_dot:")
print(multiplyJacobian(kukaId, jac_r, vel))