Real-Time Physics Simulation Forum

Re: calculateMassMatrix inconsistent with RBDL

2020-05-09T01:26:15+00:00

http://www.doc88.com/p-9833547094235.html
not sure if you can access this link, also wanted to attach the pdf for your reference but it is too large about 32M for this web. i can email to you if you need.

Statistics: Posted by steven — Sat May 09, 2020 1:26 am

Re: calculateMassMatrix inconsistent with RBDL

2020-05-08T18:32:13+00:00

Thanks Steven!

I've confirmed this works. You've helped us simplify our infrastructure significantly. If you don't mind, could you please link the original paper for bullet as well?

-rohun

Statistics: Posted by rohun — Fri May 08, 2020 6:32 pm

Re: calculateMassMatrix inconsistent with RBDL

2020-05-08T11:10:40+00:00

adding this 'flags=pb.URDF_USE_INERTIA_FROM_FILE' when loading the urdf can fix this.

Statistics: Posted by steven — Fri May 08, 2020 11:10 am

Re: calculateMassMatrix inconsistent with RBDL

2020-05-07T13:59:41+00:00

thanks for your reply, i have found the orignal paper for bullet and i will check it and try to find the cause.

Statistics: Posted by steven — Thu May 07, 2020 1:59 pm

Re: calculateMassMatrix inconsistent with RBDL

2020-05-05T17:59:56+00:00

Hi Steven,

No updates at the moment. We're trying to use the python wrapper for RBDL directly as a short term solution.

For our research we'd like to use similar controllers for both similar robots and real robots for experimentation. We've used an internal physics simulator (that uses RBDL) for real robot control and wanted to verify that pybullet produces the same mass matrix for the same robot state.

I'd appreciate it if anyone else can try running the scripts I've attached to verify the issue.

-Rohun

Statistics: Posted by rohun — Tue May 05, 2020 5:59 pm

Re: calculateMassMatrix inconsistent with RBDL

2020-04-29T01:54:42+00:00

Do you have any progress? Could you tell me why did you compare the MassMatrix between them? thanks.

Statistics: Posted by steven — Wed Apr 29, 2020 1:54 am

calculateMassMatrix inconsistent with RBDL

2020-04-21T01:19:33+00:00

Hi Erwin,

I use pybullet for operational space control on 7-dof manipulators. I've noticed some inconsistencies with the mass matrix calculated by pybullet compared to other simulation environments. I've written two small scripts that demonstrate this issue by comparing pybullet and RBDL.

To help recreate the error, I've used the panda.urdf found in bullet3 (commit f40a200) at the following filepath:
bullet3/examples/pybullet/gym/pybullet_data/franka_panda

I use pybullet 2.7.1 in a python3.5 virtual environment. I'd appreciate any help you can offer for this issue.

Pybullet

Code:

import pybullet as pbimport numpy as npphysics_id = pb.connect(pb.DIRECT)arm_id = pb.loadURDF(    fileName='/home/rohunk-local/bullet3/examples/pybullet/gym/pybullet_data/franka_panda/panda.urdf',    basePosition=[0,0,0],    baseOrientation=[0,0,0,1],    useFixedBase=True,    physicsClientId=physics_id)pb.setGravity(0, 0, -9.8, physicsClientId=physics_id)neutral_joint_angles= [0., -0.3135, 0., -2.515, 0., 2.226, 0.87]for index, angle in enumerate(neutral_joint_angles):    pb.resetJointState(        bodyUniqueId=arm_id,         jointIndex=index,         targetValue=angle,         physicsClientId=physics_id)pb.stepSimulation(physics_id)joint_positions = []for joint_index in range(7):    joint_positions.append(pb.getJointState(        arm_id,         joint_index,         physics_id)[0])print("joint positions")print(joint_positions)mass_matrix = pb.calculateMassMatrix(            bodyUniqueId=arm_id,            objPositions=joint_positions,            physicsClientId=physics_id)print("Mass Matrix")print(mass_matrix)

RBDL

Code:

#!/usr/bin/python# # rbdl mass matriximport rbdlimport numpy as npimport csvmdl = rbdl.loadModel(b'/home/rohunk-local/bullet3/examples/pybullet/gym/pybullet_data/franka_panda/panda.urdf')mass_matrix = np.zeros((9, 9 ), dtype=np.double)neutral_joint_angles= [0., -0.3135, 0., -2.515, 0., 2.226, 0.87]rbdl.CompositeRigidBodyAlgorithm(mdl, np.asarray(neutral_joint_angles, dtype=np.double),mass_matrix)

rbdl_mass_matrix.csv

pb_mass_matrix.csv

Statistics: Posted by rohun — Tue Apr 21, 2020 1:19 am