How to simulate rolling with CATIA DMU Kinematics?

A reader recently asked if I could put together a tutorial for the kinematics rolling simulation that I created. This may not be extremely detailed but should give you a pretty good idea of the steps to take when trying to simulate rolling in CATIA. This was one of the preliminary tests I ran before attempting to simulate my entire roller coaster model.


(Download the rolling in kinematocs tutorial here)

Every time you use kinematics something needs to be fixed, so the rest of the assembly moves in relation to the fixed part. In this case, the track will be fixed. Set the assembly up in assembly design then switch to the DMU Kinematics workbench when you are ready to begin simulating. You can see the constraints I used in the screen shot. It is very important to pay attention to the degrees of freedom of the system. When dealing with large assemblies, I often fully constrain the entire assembly and then go back in later and delete the constraints where I want a part to be able to move, in order to not be confused. 

Here are the joints I used to create the connected wheel rolling kinematics simulation.  To create these constraints, click “Assembly Constraints Conversion” wizard.  Create a new mechanism then click “Auto Create” and it will automatically create joints based on the constraints in the assembly. Next, you need to manually create the roll curve joints between the wheels and the track.

 

In order to create a roll curve joint you must have two curves that are tangent to one another. Here, you can see the sketch on the wheels is tangent to the sketch on the corner of the track. Double click on one of the roll curve joints and toggle the “Length Driven” option. This is your input. After you click ok you should get a message that reads “The machanism can now be simulated” and the degrees of freedom of the system  (DOF) should be zero.

In order to apply gravity to your simulation you need to create a sketch  called a “trace law.” This is essentially a graph of distance which respect to time, with the horizontal axis being time and the vertical axis being distance. A straight line gives a linear relationship, or a constant speed. Change the graph to an exponential curve and you now have acceleration.

Now you should be able to simulate two connected wheels rolling down a hill with gravity. Any questions?

Steel Roller Coaster Modeled in CATIA V5

As you can see from many of my previous posts, I spend quite a bit of time modeling roller coasters in CATIA. Well, it looks like I'm not the only one. Yunus Alapan, a student at Yildiz Technical University in Istanbul, Turkey, recently submitted a few pictures of a roller coaster he created with CATIA V5. I know from experience how hard and time consuming  it is to model a complete roller coaster by yourself, piece by piece. Hopefully, one day we will see some cars running around the track. Good job Yunus!

And since we are on the topic of CAD coasters, check out my latest simulation of the Cantilevered Roller Coaster. This time I show case the “side knocker” effect! More kinematics experimentation on the CRC model with a mismatch of new and old parts.

New 3D XML Model Uploaded to 3D Via

Today, I uploaded a new CAD model to 3D Via in 3D XML format. This is the current state of my next generation version of the cantilevered roller coaster. The main difference has been the change from a cantilevered I beam to a beefier truss configuration.

CATIA Kinematics Simulation from Manikin's POV

I am modeling a new type of roller coaster in CATIA. In order to test this new coaster concept I need to run the simulation from the viewpoint of the manikin riding in the car. Whether you are modeling a roller coaster or a sports car, here is how it is done:

First, make sure this option under Tools > Options>Ergonomics is set:

For the line of sight, create a camera in View - Named View and  then position it close to your manikin head.

 Next, attach the camera to the head of the manikin with the "attach/detach" function and change the property to perspective.

You can open a camera view window while in DMU Nav by using the Window Menu, you can open the Camera window:

Use this Camera window for recording.

 The only downside is when I simulate in the camera view it automatically switches the geometry to "shading with edges" instead of what I want to see, which is "shading with material." Anyone know if there is an option somewhere to change this?

Cantilevered Coaster Catia Kinematics Trial #5

Steam Train Piston Assembly Kinematics Simulation in CATIA

Check out the train simulation I did in CATIA V5 with the DMU Kinematics workbench! Your assembly literally has to be perfect before you can even begin to attempt kinematic simulations. Which is why I often times assemble a few pieces and then simulate a small portion of whatever it is I am building just to make sure it is working, then I add on a little more and repeat. It takes longer but is easier to diagnosis problems this way. I use an Excel spreadsheet to help me keep track of the number of degrees of freedom of each part that is not fully constrained during assembly. This seems to help me a lot. What are your strategies?

How do you write a CATIA CATScript Macro?

A question I often get asked is "how do you create vba macros in Catia?" One solution is to write a script. No, not a script for a movie, a CATScript file! To create a CATScript macro for CATIA open Notepad and write your code, then save the file with whatever name you want and type extension .CATScript instead of .txt. Here is a simple CATScript you can use as an example. This CATScript will tell you which version of Catia you are currently using, including the service pack number. Copy and paste the code into Notepad then save as CatiaVersion.CATScript.


 
Sub CATMain()

Set SystemConfiguration1 = CATIA.SystemConfiguration

Msgbox "CATIA V" & SystemConfiguration1.Version & " R " & SystemConfiguration1.Release & " sp " & SystemConfiguration1.ServicePack

End Sub


Now you are on your way to writing your own CATScript macros and automating simple and repetitive processes!

Learn how to write CATScript macros Lesson 1.

Learn how to write CATIA CATSCRIPT MACROS