Hi Mohammad, Then it's hard to say. I can only say the tracker reports what the solver sees; indeed, in the solver, X of the mesh is not modified, while Y and Z are. I don't know why it does not translate to the rendering. What I thought was since the X of the CoM truly did not change, then the X-translation you see has to be the contribution of the rotation, and that means the CoM is in fact somewhere away from the center axis of the mesh. But I cannot be sure with the given information.
Can you render a movie and share with us? If you are going to generate the movie: since you are already outputting vtk files, can you please render the mesh as, well, a mesh, instead of some points? You can load the vtk time series directly into Paraview. And if you can share the mesh file, I can probably run it myself to understand what happened. Ruochun On Tue, Jan 17, 2023 at 12:40 AM Mohammad Wasfi <[email protected]> wrote: > Hi, > > This is a picture of my mass properties page in Solidworks. I also > included a picture of the module. > > Thank you, > Mohammad > > On Monday, January 16, 2023 at 11:01:37 PM UTC-7 Ruochun Zhang wrote: > >> Are you sure the mesh you loaded from the file is centered (i.e. its MOI >> is at (0,0,0) in the mesh file)? Can you show a rendering of the >> *screw.obj* file you used in some CAD tool for us to understand? >> >> Thank you, >> Ruochun >> >> On Monday, January 16, 2023 at 10:36:03 PM UTC-6 [email protected] >> wrote: >> >>> Hi Ruochun, >>> >>> Thank you so much for your reply. I have tried to implement these >>> methods and I am experiencing something not expected. I apply the following >>> methods to my cylindrical mesh: >>> DEMSim.SetFamilyPrescribedLinVel(3, "0","none", "none", false); >>> DEMSim.SetFamilyPrescribedAngVel(3, "0", >>> to_string_with_precision(w_r), "0", false); >>> >>> my purpose is to have my cylindrical wheel spin about its axis (y-axis) >>> while disallowing linear motion in the axis perpendicular to the cylinder >>> axis (x-axis). For some reason, when I animate my simulation, my wheel is >>> spinning about its axis (which is what I want) but it is allowed to move >>> linearly in the X-direction while it is restricted to move in the >>> y-direction. However, when I obtain my mesh position through the tracker, >>> the simulation reports a change in the Y-axis but not in the x-axis. In >>> other words, my simulation animation is not consistent with my position >>> vector obtained from the simulation at each time step. For example, from >>> the simulation, my tracker returns the following values for the position: >>> Frame: 91 of 206 >>> mesh position: -0.1, -0.00142017, -0.111681 >>> >>> Frame: 92 of 206 >>> mesh position: -0.1, -0.00152285, -0.113109 >>> >>> However, in the simulation, the animation shows a movement in the >>> x-direction. I attached some pictures to demonstrate this change. >>> >>> The weird thing is when I change the SetFamilyPrescribedLinVel to >>> restrict the y-axis instead I still see the same result. I attached my >>> simulation file for your reference. >>> >>> Thank you so much, >>> >>> >>> >>> >>> >>> On Friday, January 6, 2023 at 2:48:34 PM UTC-7 Ruochun Zhang wrote: >>> >>>> Hi Mohammad, >>>> >>>> I assume you meant "restrict the motion in one direction and *disallow* >>>> it into other directions". You can do it. In fact, you can prescribe the >>>> motion in one direction while allowing free movements in other directions, >>>> too. >>>> >>>> The methods you should use are the following: >>>> >>>> *SetFamilyPrescribedLinVel* >>>> >>>> *SetFamilyPrescribedAngVel* >>>> >>>> *AddFamilyPrescribedAcc* >>>> *AddFamilyPrescribedAngAcc* >>>> >>>> A better example is DEMdemo_WheelDP.cpp >>>> <https://github.com/projectchrono/DEM-Engine/blob/main/src/demo/DEMdemo_WheelDP.cpp>. >>>> There, *DEMSim.SetFamilyPrescribedAngVel(2, "0", >>>> to_string_with_precision(w_r), "0", false)* means Family 2 will always >>>> have 0 angular velocity in X, *w_r *angular velocity in Y, and 0 >>>> angular velocity in Z. Other simulation entities cannot change the angular >>>> velocities of the entities that are in Family 2. And, >>>> *DEMSim.SetFamilyPrescribedLinVel(2, >>>> to_string_with_precision(v_ref * (1. - TR)), "0", "none", false)* >>>> further specifies that Family 2 will always be moving linearly along X at >>>> *v_ref >>>> * (1. - TR)* velocity, not moving linearly along Y, and the linear >>>> motion is not prescribed along Z, meaning if the contact/environmental >>>> forces make the entities to move along Z, it will accept these changes, >>>> unlike in X or Y directions which are prescribed. >>>> >>>> You should keep the last argument to be *false *in your case. If it is >>>> *false*, then angular/linear velocity directions/components that are >>>> not specified *or* specified with "none", will just go with the >>>> "simulation physics" (instead of any user prescription). If it is >>>> *true*, then this family's angular/linear velocity becomes prescribed >>>> unconditionally (the solver does not attempt to change them), and any >>>> unspecified components will stay at the current value (0 as default). >>>> >>>> That is for the velocities. For the 2 acceleration-related methods, you >>>> can only "add" extra accelerations to a family; you cannot prescribe the >>>> acceleration that an entity experiences, because a contact is a contact, >>>> and you cannot wipe it out. (And if you do wish to manipulate contacts, >>>> custom contact models are your friends.) You can prescribe the consequence >>>> of these forces though, and that is the velocity. >>>> >>>> The string arguments in these methods can be a number or some >>>> expressions that may involve "t", the simulation time. So you can write >>>> something like "*5 / 10*" or "*sin(3.14 * 2 * t)*" as the argument, >>>> too. More such "user-referrable variables" might be added in future >>>> versions. But if it is some super complex motion that cannot be described >>>> with a simple expression, then you are better off just fixing the family ( >>>> *SetFamilyFixed*), then using a tracker class to manually set the >>>> positions and velocities of the entity in question, step by step. >>>> >>>> Thank you, >>>> Ruochun >>>> >>>> On Thursday, January 5, 2023 at 3:28:28 PM UTC-6 [email protected] >>>> wrote: >>>> >>>>> Hi, >>>>> This is DEME related question >>>>> >>>>> Is it possible to restrict the motion in one direction and allow it >>>>> into other directions? For example, is it possible to apply some force to >>>>> an object (A) through an interaction with another object (B) and only >>>>> allow it (A) to move in the X direction when responding to that force but >>>>> not the Y and Z directions? An example code will be much appreciated. >>>>> >>>>> Thank you so much, >>>>> >>>> -- > You received this message because you are subscribed to the Google Groups > "ProjectChrono" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/projectchrono/91f6ec2b-f5b8-4014-8176-0cbd87010984n%40googlegroups.com > <https://groups.google.com/d/msgid/projectchrono/91f6ec2b-f5b8-4014-8176-0cbd87010984n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- Ruochun Zhang Email: [email protected] Email: [email protected] <[email protected]> Tel: 832-353-5111 -- You received this message because you are subscribed to the Google Groups "ProjectChrono" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. 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