Dear everyone,
We corrected the bugs reported here.
Please refer to the commit [d7193ef] on 17th April.
Welcome to feedback your test result.
在2023年3月13日星期一 UTC+1 09:14:49<Simon> 写道：
> Hi Luning,
>
> thanks for your reply. I agree on the cause of the force and torque
> components, but to my understanding the constant torque vector [0.000,
> -10.000, -0.000] would be correct only in the rotating frame, not in the
> link frame (which is fixed here).
>
> I modified my example, now using ChLinkLockLock to create the same
> rotating body setup (see below). The torque vector seems to rotate
> correctly when using ChLinkLockLock, in contrast to the
> ChLinkMotorRotationSpeed case.
>
> Thank you,
> 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});
>
> // Option 1: ChLinkMotorRotationSpeed
> // 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));
>
> // Option 2: ChLinkLockLock
> auto rotation_link{chrono_types::make_shared<ChLinkLockLock>()};
> rotation_link->Initialize(rotating_body, fixed_body, {});
> rotation_link->Set_angleset(chrono::AngleSet::ANGLE_AXIS);
> rotation_link->SetMotion_axis({0.0, 0.0, 1.0});
> rotation_link->SetMotion_ang(chrono_types::make_shared<ChFunction_Ramp>(0.0,
> 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()
> << " *** Torque: " << rotation_link->Get_react_torque()
> << " *** Link Absolute Coords: " <<
> rotation_link->GetLinkAbsoluteCoords() << "\n";
> }
>
> *Output using ChLinkMotorRotationSpeed:*
> ...
> Time: 0.970 *** Force: 0.574 0.819 10.000 *** Torque: 0.000 -10.000
> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
> 0.000
> Time: 0.980 *** Force: 0.565 0.825 10.000 *** Torque: 0.000 -10.000
> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
> 0.000
> Time: 0.990 *** Force: 0.557 0.831 10.000 *** Torque: 0.000 -10.000
> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
> 0.000
>
> *Output using ChLinkLockLock:*
> ...
> Time: 0.970 *** Force: 0.574 0.819 10.000 *** Torque: 4.662 -8.847
> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
> 0.000
> Time: 0.980 *** Force: 0.565 0.825 10.000 *** Torque: 4.707 -8.824
> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
> 0.000
> Time: 0.990 *** Force: 0.557 0.831 10.000 *** Torque: 4.751 -8.800
> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
> 0.000
>
> On Friday, March 10, 2023 at 6:27:12 PM UTC+1 [email protected] wrote:
>
>> The object is traveling in a circular motion at a constant angular
>> velocity, 1, with respect to the global z coordinate, gravity pointing
>> downward z. Therefore, link force in xy plane is a centrifugal force, F =
>> mw^2R, pointing towards origin, z component balance out gravitational
>> force. With zero angular acceleration, z-component of link torque is zero,
>> y-component balance out the torque from gravity, since rotation around y
>> and z axis are constrained.
>>
>> Thank you,
>> Luning
>>
>> On Friday, March 10, 2023 at 12:10:53 AM UTC-6 Simon wrote:
>>
>>> Hi Luning,
>>>
>>> thanks for the clarification about the link coordinate system.
>>> In my example I added the link coordinate system output to verify that
>>> it is indeed fixed to the global reference frame (see below).
>>>
>>> Unfortunately my question remains: Why does the link force vector rotate
>>> and the torque vector does not ?
>>>
>>> Thank you,
>>> 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()
>>> << " *** Torque: " << rotation_link->Get_react_torque()
>>> << " *** Link Absolute Coords: " <<
>>> rotation_link->GetLinkAbsoluteCoords() << "\n";
>>> }
>>>
>>>
>>> *Output:*
>>> ...
>>> Time: 0.830 *** Force: 0.682 0.731 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.840 *** Force: 0.675 0.738 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.850 *** Force: 0.667 0.745 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.860 *** Force: 0.660 0.751 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.870 *** Force: 0.652 0.758 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.880 *** Force: 0.645 0.764 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.890 *** Force: 0.637 0.771 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.900 *** Force: 0.629 0.777 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.910 *** Force: 0.622 0.783 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.920 *** Force: 0.614 0.790 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.930 *** Force: 0.606 0.796 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.940 *** Force: 0.598 0.802 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.950 *** Force: 0.590 0.808 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.960 *** Force: 0.582 0.813 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.970 *** Force: 0.574 0.819 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.980 *** Force: 0.565 0.825 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>> Time: 0.990 *** Force: 0.557 0.831 10.000 *** Torque: 0.000 -10.000
>>> -0.000 *** Link Absolute Coords: 0.000 0.000 0.000 1.000 0.000 0.000
>>> 0.000
>>>
>>>
>>> On Thursday, March 9, 2023 at 4:59:13 PM UTC+1 [email protected] wrote:
>>>
>>>> Hello Simon,
>>>>
>>>> "As I understand, the link coordinate system is the 'master' body
>>>> system (Body2)."
>>>> This is not correct. Your link coordinate system is defined here,
>>>>
>>>> rotation_link->Initialize(rotating_body, fixed_body, ChFrame{});
>>>>
>>>> ChFrame{} initialize a reference frame coincide with the global
>>>> reference frame. Because your Body2 (fixed_body) has the same orientation
>>>> as the GRF, and it is fixed, it just so happens that your link coordinate
>>>> system is the same as the 'master' body system.
>>>>
>>>> You can check the orientation of the link coordinate system using
>>>> this:
>>>> auto quat = rotation_link->GetLinkAbsoluteCoords().rot
>>>>
>>>> Thank you,
>>>> Luning
>>>>
>>>> On Tuesday, March 7, 2023 at 9:45:38 AM UTC-6 Simon wrote:
>>>>
>>>> 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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