4 Replies Latest reply on Dec 19, 2013 3:54 PM by Jerry Steiger

    Questions/New to SolidWorks

    Jonathan Couture



      I am fairly new to CAD and the SolidWorks community so I apologize if my questions seem simple or elementary. I am using SolidWorks 3D CAD 2013. I am familiar with making parts and  basic assemblies. I am working on a project in which I am redesigning an RC helicopter frame.  It is based on another helicopter but I want to change the power train and placement of add-on components.


      First: The helicopter is based on some currently existing parts and I am designing some new ones. I need to build/design the model around the center of gravity of the heli. In order to get the correct placement of all the components can I build basically  mock ups of the components and give them a specific weight in order to model for CG, or do I have to build each component as accurately as possible as a subassembly giving them real properties? Or will I get an accurate model if I simply make all the components from the same material? If I can assign a part a specific weight how do I do that?


      Second: Is COM in SW the same as CG? If so how do I go about testing for it in my model? I have read forum posts regarding COM so maybe I'm missing something. Part of the model is fixed because of mechanical geometry but the rest of the model can be somewhat "fluid" as need be to get proper CG. Does COM reflect current COM or does it represent where you want COM to be in an assembly?


      Thank you for your time and assitiance.




        • Re: Questions/New to SolidWorks
          Jerry Brian

          Each part can be made the correct weight by selecting material on the feature tree.

          The COM and CG will not be the same in the assembly since different parts are made of different materials.  Example. A Metal tail box vs plastic.


          It is a good idea to get the cg correct in the design but usually there is a battery pack that can be moved a little to fine tune the cg too.



          • Re: Questions/New to SolidWorks
            Matt Martens

            The answers you are looking for are all contained within the mass properties function.


            On the evaluate toolbar or tab of the command manager is the button I circled called Mass properties. It will pop up the dialog box shown. For any individual model, you can override the mass properties by the circled button. You can override any mass property (actual weight, where the CG is located, moments of inertia, etc.).  If you know those values for the detail parts I would use this to set the mass properties for those items. If you check the box "Create Center of Mass feature", you will get an icon in your feature tree and in the model window showing you where the COM or CG (they are the same thing) is. And yes, all of these functions are available in both the part and assembly environments.

              • Re: Questions/New to SolidWorks
                Jonathan Couture

                Thank you both for your advice, it was very helpful. I did notice though, when I open mass properties and override mass properties, sometimes it doesn't give me the option to insert COM point. I'm not sure why that is.


                I do know there will be a battery pack (or two) that will affect final CG of the complete model. Thanks again for your assistance.

                  • Re: Questions/New to SolidWorks
                    Jerry Steiger



                    I'm not sure how the new COM works, but in older versions you could assign a mass to a part, but that broke the ability to get the COM and moments of inertia. So it was much safer in the older versions to assign a density to your part that would give you the correct mass. If your geometry was correct and your part had a uniform density, you would get the correct values for the COM and moments of inertia.


                    Jerry S.