Enquiry abt sixDoFRigidBodyMotionConstraint for 2 axes

quarkz · December 5, 2021, 21:30

Hi,

I am trying to simulate a body in 6dof which is fixed in location (sixDoFRigidBodyMotionConstraint point) but allow to rotate along the x and y axis.

I use:

Code:

fixedAxis
        {
            sixDoFRigidBodyMotionConstraint axis;
            axis (1 1 0);
        }

Is this correct? It's running and my results show that z axis is almost fixed:

Angular velocity: (0.0160949 0.0150073 5.55402e-12)

Or is it actually constrained to rotate along the (1 1 0) axis, which seems to be a bit different

Hope someone can help. Thanks.

quarkz · May 20, 2022, 03:13

Hi all,

I realised that if I use (1 1 0) axis, it will restrict motion along a line (1 1 0) axis.

Since what I wanted is dof along x and y, I should restrict along the xy plane:

NameofPlaneConstraint
{
sixDoFRigidBodyMotionConstraint plane;
normal (0 0 1);
}

quarkz · January 11, 2023, 03:36

I need to clarify that using the plane constraint allows x,y translation along the plane. However, allowing rotation along only x and y axes doesn't seem possible.

It's either rotations along x,y,z using point constraint, or only 1 axis using axis constraint.

Please correct me if I'm wrong.

December 5, 2021, 21:30	Enquiry abt sixDoFRigidBodyMotionConstraint for 2 axes	#1
quarkz Senior Member TWB Join Date: Mar 2009 Posts: 414 Rep Power: 19	Hi, I am trying to simulate a body in 6dof which is fixed in location (sixDoFRigidBodyMotionConstraint point) but allow to rotate along the x and y axis. I use: Code: fixedAxis { sixDoFRigidBodyMotionConstraint axis; axis (1 1 0); } Is this correct? It's running and my results show that z axis is almost fixed: Angular velocity: (0.0160949 0.0150073 5.55402e-12) Or is it actually constrained to rotate along the (1 1 0) axis, which seems to be a bit different Hope someone can help. Thanks.

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May 20, 2022, 03:13		#2
quarkz Senior Member TWB Join Date: Mar 2009 Posts: 414 Rep Power: 19	Hi all, I realised that if I use (1 1 0) axis, it will restrict motion along a line (1 1 0) axis. Since what I wanted is dof along x and y, I should restrict along the xy plane: NameofPlaneConstraint { sixDoFRigidBodyMotionConstraint plane; normal (0 0 1); }

January 11, 2023, 03:36		#3
quarkz Senior Member TWB Join Date: Mar 2009 Posts: 414 Rep Power: 19	I need to clarify that using the plane constraint allows x,y translation along the plane. However, allowing rotation along only x and y axes doesn't seem possible. It's either rotations along x,y,z using point constraint, or only 1 axis using axis constraint. Please correct me if I'm wrong.