title: Bullet physics mass center and weird object reaction
body: <p>I am new in bullet, and i have probably a basic problem.
  I try to simulate bowing pin falling, but they after falling down, getting up by themselves without any force added. </p>
  
  <p>I wonder where is my mistake, can anyone of you help, i would be grateful. </p>
  
  <p>here is a video showing what happens: 
  <a href="https://www.sendspace.com/file/78tncr" rel="nofollow">https://www.sendspace.com/file/78tncr</a></p>
  
  <p>and here is how I added floor :</p>
  
  <pre><code>tTransform l;
  l.setIdentity();
  l.setOrigin(btVector3(0,0,0));
  btStaticPlaneShape* plane=new btStaticPlaneShape(btVector3(0,1,0),0);
  btMotionState* motion=new btDefaultMotionState(l);
  btRigidBody::btRigidBodyConstructionInfo info(0.0,motion,plane);
  btRigidBody* body=new btRigidBody(info);
  world-&gt;addRigidBody(body);
  bodies.push_back(body);
  </code></pre>
  
  <p>and this is how I added bolwing pin : </p>
  
  <pre><code>btRigidbodyaddBolw (float x, float y , float z,float mass)
  {
  btTransform t;  
  t.setIdentity();
  t.setOrigin(btVector3(x,y,z));
  btTriangleMesh * tmptri= new btTriangleMesh();
  //this is simply reading from std::vector, where I have vertex of a shape
  for(int i=0;i&lt;=faces.size()-3;i=i+3)
  {
      if(faces[i].wektor==-100)
      {
          i=i-2;
          continue;
      }
      btVector3 vertex1(vertexy[faces[i].wektor].GetX(), vertexy[faces[i].wektor].GetY(), vertexy[faces[i].wektor].GetZ());
      btVector3 vertex2(vertexy[faces[i+1].wektor].GetX(), vertexy[faces[i+1].wektor].GetY(), vertexy[faces[i+1].wektor].GetZ());
      btVector3 vertex3(vertexy[faces[i+2].wektor].GetX(), vertexy[faces[i+2].wektor].GetY(), vertexy[faces[i+2].wektor].GetZ());
  
      tmptri-&gt;addTriangle(vertex1, vertex2, vertex3);
  }
  btConvexShape *tmpshape = new btConvexTriangleMeshShape(tmptri);
  btShapeHull *hull = new btShapeHull(tmpshape);
  btScalar margin = tmpshape-&gt;getMargin();
  hull-&gt;buildHull(margin);
  btConvexHullShape* simplifiedConvexShape = new btConvexHullShape();
  for (int i=0;i&lt;hull-&gt;numVertices();i++)
  {
      simplifiedConvexShape-&gt;addPoint(hull-&gt;getVertexPointer()[i]);   
  }
  delete tmpshape;
  delete hull;
  btMotionState * motion = new btDefaultMotionState(t);
  btVector3 inertia(0,0,0);
  if(mass!=0.0)
      simplifiedConvexShape-&gt;calculateLocalInertia(mass,inertia); 
  btRigidBody::btRigidBodyConstructionInfo info(mass,motion,simplifiedConvexShape,inertia);
  btRigidBody* body=new btRigidBody(info);
  world-&gt;addRigidBody(body);  //and let the world know about it
  bodies.push_back(body); //to be easier to clean, I store them a vector
  return body;
  }
  </code></pre>
  
  <p>I tried change shape of pin, mass, friction and restitution but nothing hepl, is there any way to change center of mass, maybe it would help?</p>