Hi,
thank you for the updated implementation. I re-ran my test case with chrono
at commit 841781d6e0e4b09c68cd431e1f7381b402f17ad1.
The reaction torque vector does now rotate as expected with
ChLinkMotorRotationSpeed. As shown in my example below there is now a
constant angle difference of 90° between force and torque in the x-y plane.
However, with the ChLinkLockLock implementation I noticed that the angle of
the torque vector seems to change only at half the speed of the body
rotation. This leads to a constantly changing difference between force and
torque direction in the x-y plane.
So perhaps there is also something wrong with the ChLinkLockLock's reaction
torque direction (see example with output below).
Sorry for being naggy, your support is highly appreciated!
Best regards,
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);
const auto body_position{rotating_body->GetPos()};
const double body_angle{std::atan2(body_position[1], body_position[0])};
const auto reaction_force{rotation_link->Get_react_force()};
const double force_angle{std::atan2(reaction_force[1],
reaction_force[0])};
const auto reaction_torque{rotation_link->Get_react_torque()};
const double torque_angle{std::atan2(reaction_torque[1],
reaction_torque[0])};
std::cout << std::fixed << std::setprecision(3) << "Time: " <<
system.GetChTime()
<< " *** Body Angle: " << body_angle << " *** Force Angle: "
<< force_angle
<< " *** Torque Angle: " << torque_angle
<< " *** Angle Difference: " << force_angle - torque_angle <<
"\n";
}
*Output using ChLinkMotorRotationSpeed:*
...
Time: 0.950 *** Body Angle: 0.950 *** Force Angle: 0.940 *** Torque Angle:
-0.631 *** Angle Difference: 1.571
Time: 0.960 *** Body Angle: 0.960 *** Force Angle: 0.950 *** Torque Angle:
-0.621 *** Angle Difference: 1.571
Time: 0.970 *** Body Angle: 0.970 *** Force Angle: 0.960 *** Torque Angle:
-0.611 *** Angle Difference: 1.571
Time: 0.980 *** Body Angle: 0.980 *** Force Angle: 0.970 *** Torque Angle:
-0.601 *** Angle Difference: 1.571
Time: 0.990 *** Body Angle: 0.990 *** Force Angle: 0.980 *** Torque Angle:
-0.591 *** Angle Difference: 1.571
*Output using ChLinkLockLock:*
...
Time: 0.950 *** Body Angle: 0.950 *** Force Angle: 0.940 *** Torque Angle:
-1.096 *** Angle Difference: 2.036
Time: 0.960 *** Body Angle: 0.960 *** Force Angle: 0.950 *** Torque Angle:
-1.091 *** Angle Difference: 2.041
Time: 0.970 *** Body Angle: 0.970 *** Force Angle: 0.960 *** Torque Angle:
-1.086 *** Angle Difference: 2.046
Time: 0.980 *** Body Angle: 0.980 *** Force Angle: 0.970 *** Torque Angle:
-1.081 *** Angle Difference: 2.051
Time: 0.990 *** Body Angle: 0.990 *** Force Angle: 0.980 *** Torque Angle:
-1.076 *** Angle Difference: 2.056
On Monday, April 17, 2023 at 4:48:39 PM UTC+2 [email protected] wrote:
> 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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