Hi,
as per the documentation
<https://api.projectchrono.org/classchrono_1_1_ch_link_motor_rotation_speed.html>,
ChLinkMotorRotationSpeed's member functions Get_react_force() and
Get_react_torque() return the respective values in link coordinates.
As I understand, the link coordinate system is the 'master' body system
(Body2).
In the example below a body rotates around the absolute z axis using
ChLinkMotorRotationSpeed (the 'master' body is fixed here). As expected,
the link reaction force consists of a the constant body weight in z
direction and the rotating centrifugal load in the x-y plane. However, the
reaction torque (due to gravity) is constant despite the link's rotation.
Shouldn't the torque vector also rotate or do I misunderstand something?
Thanks in advance!
Simon
*Code: *
ChSystemNSC system{};
auto fixed_body{chrono_types::make_shared<ChBody>()};
fixed_body->SetBodyFixed(true);
auto rotating_body{chrono_types::make_shared<ChBody>()};
rotating_body->SetPos({1.0, 0.0, 0.0});
auto rotation_link{chrono_types::make_shared<ChLinkMotorRotationSpeed>()};
rotation_link->Initialize(rotating_body, fixed_body, ChFrame{});
rotation_link->SetSpeedFunction(chrono_types::make_shared<ChFunction_Const>(1.0));
system.Add(fixed_body);
system.Add(rotating_body);
system.Add(rotation_link);
system.Set_G_acc({0.0, 0.0, 10.0});
for (double time{}; time < 1.0; time += 0.01)
{
system.DoFrameDynamics(time);
std::cout << std::fixed << std::setprecision(3) << "Time: " <<
system.GetChTime()
<< " *** Force: " << rotation_link->Get_react_force()
<< " *** Moment: " << rotation_link->Get_react_torque() <<
"\n";
}
*Output: ...*
Time: 0.810 *** Force: 0.697 0.717 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.820 *** Force: 0.690 0.724 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.830 *** Force: 0.682 0.731 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.840 *** Force: 0.675 0.738 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.850 *** Force: 0.667 0.745 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.860 *** Force: 0.660 0.751 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.870 *** Force: 0.652 0.758 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.880 *** Force: 0.645 0.764 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.890 *** Force: 0.637 0.771 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.900 *** Force: 0.629 0.777 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.910 *** Force: 0.622 0.783 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.920 *** Force: 0.614 0.790 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.930 *** Force: 0.606 0.796 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.940 *** Force: 0.598 0.802 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.950 *** Force: 0.590 0.808 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.960 *** Force: 0.582 0.813 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.970 *** Force: 0.574 0.819 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.980 *** Force: 0.565 0.825 10.000 *** Moment: 0.000 -10.000
-0.000
Time: 0.990 *** Force: 0.557 0.831 10.000 *** Moment: 0.000 -10.000
-0.000
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