Simulation of spinning top collision

[kuwt]

Hello project chrono community,

I want to simulate the collision of two spinning top using project chrono. However, I encounter a weird problem that the two spinning top goes towards each other. v0.mp4 is a video showing how they go towards each other.. v1.mp4 is a video showing another viewing angle. I release the two spinning top mid air with some angular velocity and let them drop to the floor. I expect they will go towards each other after they hit the floor but not during initially mid air. I inserted the object as shown in the following code script(whole minimal script attached as spinningtop2.cpp. The resources are attached too. I made the floor myself. The spinning tops are from github as mentioned in the code.):

auto falling = chrono_types::make_shared<ChBodyEasyMesh>(

"../resource/spinningTop1.obj",7000,true,true,true,contact_mat,0.005);

falling->SetRot(QuatFromAngleY(180 * CH_DEG_TO_RAD));

falling->SetPos(ChVector3d(3, 0, 0));

falling->SetAngVelLocal(ChVector3d(0,0, 5));

sys.Add(falling);

auto falling2 = chrono_types::make_shared<ChBodyEasyMesh>(

"../resource/spinningTop2.obj",7000,true,true,true,contact_mat,0.005);

falling2->SetRot(QuatFromAngleY(180 * CH_DEG_TO_RAD));

falling2->SetPos(ChVector3d(-3, 0, 0));

falling2->SetAngVelLocal(ChVector3d(0,0, 5));

sys.Add(falling2);

auto floor = chrono_types::make_shared<ChBodyEasyMesh>(

"../resource/floor.obj",7000,true,true,true,contact_mat,0.005);

floor->SetPos(ChVector3d(0, 0, -3));

floor->SetFixed(true);

sys.Add(floor);

Does anybody know what I have misunderstood? Thank you.

[kuwt]

Interestingly if I change the object from mesh to simple ChBodyEasyBox(as shown below). The weird attraction disappears(video a.mp4). I am not sure if I misunderstand

anything for ChBodyEasyMesh. Forgot to mention that i'm using version release 9.0.

// auto falling = chrono_types::make_shared<ChBodyEasyMesh>("../resource/spinningTop1.obj",7000,true,true,true,contact_mat,0.005);

auto falling = chrono_types::make_shared<ChBodyEasyBox>(2,2,2,7000,true,true,contact_mat);

falling->SetRot(QuatFromAngleY(180 * CH_DEG_TO_RAD));

falling->SetPos(ChVector3d(3, 0, 0));

falling->SetAngVelLocal(ChVector3d(0,0, 5));

sys.Add(falling);

// auto falling2 = chrono_types::make_shared<ChBodyEasyMesh>( "../resource/spinningTop2.obj",7000,true,true,true,contact_mat,0.005);

auto falling2 = chrono_types::make_shared<ChBodyEasyBox>(2,2,2,7000,true,true,contact_mat);

[Radu Serban]

This is a cute simulation.

 

From the code you provided, I take it that you are using an older version of Chrono. I just tried your code with the latest Chrono from the main git branch, and I cannot reproduce the issue.

 

Regarding your question about ChBodyEasMesh, note that this creates under the hood a ChBodyAuxRef (and not a ChBody).  In that case, you probably want to control the pose of the reference frame with respect to the global frame. However, SetPos and SetRot actually affect the pose of the centroidal frame (relative to the global frame).

I know that this is *very* confusing and it’s something I intend to change throughout Chrono whenever I will find the time.

 

In the meantime, I suggest you

• Use the latest code in the Chrono main branch
• Switch to using Chrono::VSG for run-time visualization (better than Irrlicht)

 

I attached a modification of your code where I

• Changed the way the initial body poses are set
• Used Chrono::VSG for run-time visualization
• Flipped one of the spinning tops
• Increased the initial angular velocities to 50 rad/s

 

Let me know what you get.

 

Radu

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