Problem with changing the friction coefficient between robot's feet and ground

[raisimtech]

Problem with changing the friction coefficient between robot's feet and ground

[edward9503]

Hi @jhwangbo ,

suddenly I have a second question: how can we draw a point, a line or a polygon in raisimOgre?

Thanks in advance.

Best

[jhwangbo]

1. what you did looks correct. Can you change the friction coefficient to 0.001 and check if it slips?
2. https://github.com/raisimTech/raisimOgre/blob/master/examples/src/visualObjects/visualObjects.cpp

[edward9503]

Thanks for the reply.

For the friction coefficient, it still didn't slip even I changed it to 0.001. It seems weird to me because I just followed the tutorial from the website. I am using the world.integrate1() and world.integrate2() for the simulation, could they be the problem?

Best

[edward9503]

Hi, any update on this? @jhwangbo

[edward9503]

@jhwangbo After that, I also changed the bouncy coefficient in raisimOgre, this also didn't work. Any feedback?
Thanks!

[jhwangbo]

Can you share a minimal code to reproduce the error?

[edward9503]

So the code looks like this:

void setupCallback() {
    auto vis = raisim::OgreVis::get();

    /// light
    vis->getLight()->setDiffuseColour(1, 1, 1);
    vis->getLight()->setCastShadows(true);
    Ogre::Vector3 lightdir(1., 1, -1);
    lightdir.normalise();
    vis->getLight()->setDirection(lightdir);
    vis->setContactVisObjectSize(0.04, 0.3);

    /// load  textures
    vis->addResourceDirectory(vis->getResourceDir() + "/material/checkerboard");
    vis->loadMaterialFile("checkerboard.material");

    /// shadow setting
    vis->getSceneManager()->setShadowTechnique(Ogre::SHADOWTYPE_TEXTURE_ADDITIVE);
    vis->getSceneManager()->setShadowTextureSettings(2048, 3);

    // beyond this distance, shadow disappears
    vis->getSceneManager()->setShadowFarDistance(10);
    // size of contact points and contact forces
    vis->setContactVisObjectSize(0.01, 0.4);
    // speed of camera motion in freelook mode
    vis->getCameraMan()->setTopSpeed(5);
}

// The visualizer we want to execute on the new thread.
void raisimOgre_visualizer()
{
    auto vis = raisim::OgreVis::get();
    
    /// these method must be called before initApp
    vis->setWorld(&world);
    vis->setWindowSize(1800, 1200);
    vis->setImguiSetupCallback(imguiSetupCallback);
    vis->setImguiRenderCallback(imguiRenderCallBack);
    vis->setSetUpCallback(setupCallback);
    vis->setAntiAliasing(8);
    raisim::gui::manualStepping = false;

    /// starts visualizer thread
    vis->initApp();  

    /// create raisim objects
    auto ground = world.addGround(0, "checkerboard_green");    

    /// create visualizer objects
    vis->createGraphicalObject(ground, 20, "floor", "checkerboard_green");   

    anymal_visual.push_back(vis->createGraphicalObject(anymal.back(), "ANYmal_kinova"));

    while(ros::ok()){
        vis->renderOneFrame();
}
}

int main(int argc, char **argv) {
    anymal.push_back(world.addArticulatedSystem(raisim::loadResource("anymal_modified.urdf")));

    // Run the visualizer thread
    std::thread t1(raisimOgre_visualizer);

    anymal.back()->setGeneralizedCoordinate({0,0,0.57,......});
    anymal.back()->setGeneralizedForce(Eigen::VectorXd::Zero(anymal.back()->getDOF()));
    anymal.back()->setControlMode(raisim::ControlMode::PD_PLUS_FEEDFORWARD_TORQUE);
    anymal.back()->setPdGains(jointPgain, jointDgain);
    anymal.back()->setPdTarget(jointNominalConfig, jointVelocityTarget);

    // Set friction coefficient
    anymal.back()->getCollisionBody("LF_FOOT/0").setMaterial("LF_FOOT");
    anymal.back()->getCollisionBody("RF_FOOT/0").setMaterial("RF_FOOT");
    anymal.back()->getCollisionBody("LH_FOOT/0").setMaterial("LH_FOOT");
    anymal.back()->getCollisionBody("RH_FOOT/0").setMaterial("RH_FOOT");
    world.setMaterialPairProp("checkerboard_green", "LF_FOOT", 0.8, 0, 0);
    world.setMaterialPairProp("checkerboard_green", "RF_FOOT", 0.8, 0, 0);
    world.setMaterialPairProp("checkerboard_green", "LH_FOOT", 0.8, 0, 0);
    world.setMaterialPairProp("checkerboard_green", "RH_FOOT", 0.8, 0, 0);

    while (ros::ok()){
        // Set the world time and do the integration 1
        ros::Time begin = ros::Time::now();
        ros::Time current_t = begin;
        auto dt = (current_t - lastTimeStampt).toSec(); 
        world.setTimeStep(dt);

        world.integrate1();

        // Here always calculates my commanded torque
       torque = some_tracking_controller();

       anymal.back()->setPdGains(jointPgain, jointDgain);  
       anymal.back()->setPdTarget(jointsPTarget, jointVelocityTarget);
       anymal.back()->setGeneralizedForce(torque);

       world.integrate2();
}

        ros::spinOnce();
        loop_rate.sleep();

}

Thanks a lot for any feedback!

Best

[jhwangbo]

This code works for me. I see clear differences when I change the friction coefficient. Do you have the latest version?

[edward9503]

Something weird happed. After I cloned the latest version of raisimLib and merge my local raisimLib (actually I didn't change this repo before from the original one) into the newest raisimLib, there is an error occurring during initializing the PD gains: "p gains should have the same dimension as the degrees of freedom". I went into the ArticulatedSystem.hpp and printed the dof dimension out. It sometimes became 0, sometimes became a very large number. I don't know what happens since I didn't change my code and just get the latest raisimLib from git. Any tipps for this problem?

Best

[jhwangbo]

This happens if you have multiple versions of raisim in your system

[edward9503]

Thanks, you are right, I have installed an old version raisim locally in some other directories. After updating it to the latest one, problem's solved.

However, when I change the friction coefficient again, I still cannot see the clear differences. Any tipps?

[jhwangbo]

Change only one foot. Then you should see the difference.

[edward9503]

Nope. It still walks fine without any slip. Really confusing.

[edward9503]

Change only one foot. Then you should see the difference.

I also changed the bouncy coefficient to a larger value, like 2, but I also didn't see the contact becoming bouncier.

[jhwangbo]

Can you change only one foot to 0.01 and share the code and video?

[jhwangbo]

I added an example here. https://github.com/raisimTech/raisimLib/blob/7bad35165b7fb91bc4401bcefe22244c97551afd/examples/src/server/anymals.cpp#L48
This seems to work fine on my machine. Let me know if this example doesn't work for you

[jhwangbo]

you have to uncomment the two lines to see the effect

[edward9503]

Hi @jhwangbo
Sorry for the late reply. I did what you suggested, but still, it didn't affect the results that much.

Here are the codes before setting the friction coefficient to 0.01:

void setupCallback() {
    auto vis = raisim::OgreVis::get();

    /// light
    vis->getLight()->setDiffuseColour(1, 1, 1);
    vis->getLight()->setCastShadows(true);
    Ogre::Vector3 lightdir(1., 1, -1);
    lightdir.normalise();
    vis->getLight()->setDirection(lightdir);
    vis->setContactVisObjectSize(0.04, 0.3);

    /// load  textures
    vis->addResourceDirectory(vis->getResourceDir() + "/material/checkerboard");
    vis->loadMaterialFile("checkerboard.material");

    /// shadow setting
    vis->getSceneManager()->setShadowTechnique(Ogre::SHADOWTYPE_TEXTURE_ADDITIVE);
    vis->getSceneManager()->setShadowTextureSettings(2048, 3);

    // beyond this distance, shadow disappears
    vis->getSceneManager()->setShadowFarDistance(10);
    // size of contact points and contact forces
    vis->setContactVisObjectSize(0.01, 0.4);
    // speed of camera motion in freelook mode
    vis->getCameraMan()->setTopSpeed(5);
}

// The visualizer we want to execute on the new thread.
void raisimOgre_visualizer()
{
    auto vis = raisim::OgreVis::get();
    
    /// these method must be called before initApp
    vis->setWorld(&world);
    vis->setWindowSize(1800, 1200);
    vis->setImguiSetupCallback(imguiSetupCallback);
    vis->setImguiRenderCallback(imguiRenderCallBack);
    vis->setSetUpCallback(setupCallback);
    vis->setAntiAliasing(8);
    raisim::gui::manualStepping = false;

    /// starts visualizer thread
    vis->initApp();  

    /// create raisim objects
    auto ground = world.addGround(0, "checkerboard_green");    

    /// create visualizer objects
    vis->createGraphicalObject(ground, 20, "floor", "checkerboard_green");   

    anymal_visual.push_back(vis->createGraphicalObject(anymal.back(), "ANYmal_kinova"));

    while(ros::ok()){
        vis->renderOneFrame();
}
}

int main(int argc, char **argv) {
    anymal.push_back(world.addArticulatedSystem(raisim::loadResource("anymal_modified.urdf")));

    // Run the visualizer thread
    std::thread t1(raisimOgre_visualizer);

    anymal.back()->setGeneralizedCoordinate({0,0,0.57,......});
    anymal.back()->setGeneralizedForce(Eigen::VectorXd::Zero(anymal.back()->getDOF()));
    anymal.back()->setControlMode(raisim::ControlMode::PD_PLUS_FEEDFORWARD_TORQUE);
    anymal.back()->setPdGains(jointPgain, jointDgain);
    anymal.back()->setPdTarget(jointNominalConfig, jointVelocityTarget);

    // Set friction coefficient
    // anymal.back()->getCollisionBody("LH_FOOT/0").setMaterial("LH_FOOT");
    // world.setMaterialPairProp("checkerboard_green", "LH_FOOT", 0.01, 0, 0);

    while (ros::ok()){
        // Set the world time and do the integration 1
        ros::Time begin = ros::Time::now();
        ros::Time current_t = begin;
        auto dt = (current_t - lastTimeStampt).toSec(); 
        world.setTimeStep(dt);

        world.integrate1();

        // Here always calculates my commanded torque
       torque = some_tracking_controller();

       anymal.back()->setPdGains(jointPgain, jointDgain);  
       anymal.back()->setPdTarget(jointsPTarget, jointVelocityTarget);
       anymal.back()->setGeneralizedForce(torque);

       world.integrate2();
}

        ros::spinOnce();
        loop_rate.sleep();

}

The LH_FOOT means this:

For the experiment, I did backward walking, then sideways walking. And the video is attached here:
https://user-images.githubusercontent.com/39060488/152913049-8867b727-f2f8-43bf-9123-596af5f10c31.mp4

After that, I set the friction coefficient to 0.01, here are the codes:

void setupCallback() {
    auto vis = raisim::OgreVis::get();

    /// light
    vis->getLight()->setDiffuseColour(1, 1, 1);
    vis->getLight()->setCastShadows(true);
    Ogre::Vector3 lightdir(1., 1, -1);
    lightdir.normalise();
    vis->getLight()->setDirection(lightdir);
    vis->setContactVisObjectSize(0.04, 0.3);

    /// load  textures
    vis->addResourceDirectory(vis->getResourceDir() + "/material/checkerboard");
    vis->loadMaterialFile("checkerboard.material");

    /// shadow setting
    vis->getSceneManager()->setShadowTechnique(Ogre::SHADOWTYPE_TEXTURE_ADDITIVE);
    vis->getSceneManager()->setShadowTextureSettings(2048, 3);

    // beyond this distance, shadow disappears
    vis->getSceneManager()->setShadowFarDistance(10);
    // size of contact points and contact forces
    vis->setContactVisObjectSize(0.01, 0.4);
    // speed of camera motion in freelook mode
    vis->getCameraMan()->setTopSpeed(5);
}

// The visualizer we want to execute on the new thread.
void raisimOgre_visualizer()
{
    auto vis = raisim::OgreVis::get();
    
    /// these method must be called before initApp
    vis->setWorld(&world);
    vis->setWindowSize(1800, 1200);
    vis->setImguiSetupCallback(imguiSetupCallback);
    vis->setImguiRenderCallback(imguiRenderCallBack);
    vis->setSetUpCallback(setupCallback);
    vis->setAntiAliasing(8);
    raisim::gui::manualStepping = false;

    /// starts visualizer thread
    vis->initApp();  

    /// create raisim objects
    auto ground = world.addGround(0, "checkerboard_green");    

    /// create visualizer objects
    vis->createGraphicalObject(ground, 20, "floor", "checkerboard_green");   

    anymal_visual.push_back(vis->createGraphicalObject(anymal.back(), "ANYmal_kinova"));

    while(ros::ok()){
        vis->renderOneFrame();
}
}

int main(int argc, char **argv) {
    anymal.push_back(world.addArticulatedSystem(raisim::loadResource("anymal_modified.urdf")));

    // Run the visualizer thread
    std::thread t1(raisimOgre_visualizer);

    anymal.back()->setGeneralizedCoordinate({0,0,0.57,......});
    anymal.back()->setGeneralizedForce(Eigen::VectorXd::Zero(anymal.back()->getDOF()));
    anymal.back()->setControlMode(raisim::ControlMode::PD_PLUS_FEEDFORWARD_TORQUE);
    anymal.back()->setPdGains(jointPgain, jointDgain);
    anymal.back()->setPdTarget(jointNominalConfig, jointVelocityTarget);

    // Set friction coefficient
    anymal.back()->getCollisionBody("LH_FOOT/0").setMaterial("LH_FOOT");
    world.setMaterialPairProp("checkerboard_green", "LH_FOOT", 0.01, 0, 0);

    while (ros::ok()){
        // Set the world time and do the integration 1
        ros::Time begin = ros::Time::now();
        ros::Time current_t = begin;
        auto dt = (current_t - lastTimeStampt).toSec(); 
        world.setTimeStep(dt);

        world.integrate1();

        // Here always calculates my commanded torque
       torque = some_tracking_controller();

       anymal.back()->setPdGains(jointPgain, jointDgain);  
       anymal.back()->setPdTarget(jointsPTarget, jointVelocityTarget);
       anymal.back()->setGeneralizedForce(torque);

       world.integrate2();
}

        ros::spinOnce();
        loop_rate.sleep();

}

And the result looks like this:
https://user-images.githubusercontent.com/39060488/152915448-410e579d-e1f3-4776-b516-e9c1cb38f38c.mp4

From my point of view, I didn't see any clear difference. So I think changing the coefficient like this may not work.

P.S. I have noticed one thing: in your example code, you are using the raisim server. And after setting the coefficient, you directly send this change to the server. But in my case, I am using the world.integrate 1 and 2 for simulating the result. Perhaps, the integrator didn't involve these coefficient changes? There are only the differences between my codes and yours. Any suggestion?

Thanks.

[jhwangbo]

"LH_FOOT/0" for the ANYmalC robot is the shank, not the foot. Please check your URDF

[edward9503]

Thanks for the reply.

Since "LH_FOOT/0" means the first collision body of the link “LH_FOOT”, it is indeed the "LH_shank_fixed" if I understand correctly from urdf. Right?

Following questions come up to my mind:

1. Then for changing the friction coefficient in ANYmal C, should I use "LH_FOOT" instead of "LH_FOOT/0" (i.e., set "anymal.back()->getCollisionBody("LH_FOOT").setMaterial("LH_FOOT");")?
2. If not, how should I do to select the foot?
3. Moreover, why does the LH_FOOT link of ANYmal C have two collision properties (i.e., one for the adapter and another for the foot), where these properties are separated into link "LH_FOOT" and "LH_ADAPTER" respectively?
4. In ANYmal B, "LH_FOOT/0" should be the link “ LH_ADAPTER” right? But I checked the collision body of this link, it is also the adapter, which causes the internal collision. So I was confused why "LH_FOOT/0" can be used in ANYmal B and cannot be used in C?

Thanks.

[jhwangbo]

Can you post this question to raisimLib repo? I'll write a detailed answer but this is not the right repo to share.

[edward9503]

Sure. I will find a time to write a question there. Thanks!