Real-Time Physics Simulation Forum 2019-02-19T00:08:29+00:00 https://pybullet.org/Bullet/phpBB3/app.php/feed/topic/12611 2019-02-19T00:08:29+00:00 2019-02-19T00:08:29+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=41873#p41873 <![CDATA[Re: Undesired behaviour when dropping cube]]> p.changeDynamics(boxId,-1,linearDamping=0, angularDamping=0)

In addition, there is a maximum velocity of 100 units (m/s for linear velocity and radians/sec for angular velocity).
If this is an issue, you can compile PyBullet from source, and increase m_maxCoordinateVelocity in Bullet/src/BulletDynamics/Featherstone/btMultiBody.cpp

Statistics: Posted by Erwin Coumans — Tue Feb 19, 2019 12:08 am

]]> 2019-02-18T13:09:21+00:00 2019-02-18T13:09:21+00:00 https://pybullet.org/Bullet/phpBB3/viewtopic.php?p=41872#p41872 <![CDATA[Undesired behaviour when dropping cube]]>
I recently started using PyBullet and want to thank you for this awesome piece of software. However, during some trials I found some weird behavior when dropping a simple cube from 100 meters: The velocity seems to stall asymptotically. This probably has to do with some stabilization of the simulation, but I could not find any information on this in the documentation. Could you give me a hint please? I attached the code and a plot.

Thank you in advance.

Best regards
Image

Code: 

import pybullet as pimport pybullet_dataimport numpy as npimport matplotlib.pyplot as plttimestep = 1 / 240g = -10physicsClient = p.connect(p.DIRECT)p.setAdditionalSearchPath(pybullet_data.getDataPath())p.setGravity(0, 0, g)planeId = p.loadURDF("plane.urdf")cubeStartPos = [0, 0, 100]cubeStartOrientation = p.getQuaternionFromEuler([0, 0, 0])boxId = p.loadURDF("cube.urdf", cubeStartPos, cubeStartOrientation)p.setTimeStep(timestep)simulated_velocity_list = []physical_velocity_list = []time = []i = 0while True:    time.append(i * timestep)    physical_velocity_list.append(g * i * timestep)    simulated_velocity_list.append(p.getBaseVelocity(boxId)[0][2])    if (p.getBasePositionAndOrientation(boxId)[0][2] <= 0.05):        print(i * timestep)        break    p.stepSimulation()    i += 1plt.plot(time, simulated_velocity_list)plt.plot(time, physical_velocity_list)plt.grid()plt.xlabel("Time [s]")plt.ylabel("Velocity [mps]")plt.legend(["PyBullet", "v=a t"])plt.show()p.disconnect()

Statistics: Posted by robotguy — Mon Feb 18, 2019 1:09 pm

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