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For engineers who already know the math—but still lose projects. For the last few years, I’ve been sharing technical guides here on Mechanical Design Handbook —how to size a motor, how to calculate fits, and (as you recently read) how to choose between timing belts and ball screws. But after 25 years in industrial automation, I realized something uncomfortable: Projects rarely fail because the math was wrong. They fail because: The client changed the scope three times in one week. A critical vendor lied about a shipping date (and no one verified it). The installation technician couldn’t fit a wrench into the gap we designed. University taught us the physics. It didn’t teach us the reality. That gap is why I wrote my new book, The Sheet Mechanic . This is not a textbook. It is a field manual for the messy, political, and chaotic space between the CAD model and the factory floor. It captures the systems I’ve used to survive industrial projec...
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Dynamic Simulation Tutorial: Setting up 3D Contact in UG NX4 Motion

Which software are you using in your mechanical design project?

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I have been using Solid Edge 3D CAD software for 1-2 years for my mechanical design projects in the past. But now, according to the standardization in my design organization, I have to switch to use Unigraphics software instead, or we call it in short as "UG NX4" (the latest versions are simply called NX).

To be honest, at first, I still liked Solid Edge because I think I can make modeling and assembly in Solid Edge faster and easier than in UG. But one of the good things for UG is the Motion Simulation module that helps me simulate the movement of mechanical assemblies before releasing for manufacturing. I know that Solid Edge also has this kind of simulation module, but I didn't have a chance to use it (no license). So in this post, I would like to share how easy it is to set up motion simulation in UG NX4.

Let's start with a very simple modeling.

I would like to see how the cylinder moves when it is pushed by the rotating lever. So I start by making UG modeling as shown above. Those parts can be "features" in a single UG file or the assembly of several UG files.

Once the assembly is ready, I can then start "Motion Simulation".

At Motion Navigator, right-click and select "New Simulation".

UG NX4 will show the pop-up Motion Joint Wizard window for automatic setting of joints for simulation. For this example, I just click the cancel button in order to set the links and joints manually.

Next, what I have to do is to set necessary links and joints for motion simulation. I have to start with the creation of links. Parts or features that cannot be moved and have no contact with other parts can be excluded from the link setting. In the example, the fixed column can be excluded from link setting. I can leave it as it is, just for showing purposes only.

First, I would set the lever as a link in motion simulation by clicking at the "link" icon and selecting the lever and renaming it as "lever".

Do the same thing for the cylinder and the block.
Why do I need to set the block as a link?

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I have to set the block as a link even though it is not moving because I would like to set the 3D contact between the cylinder and the block, otherwise, the cylinder will fall down during simulation! I have to also select "fix the link" for the block in order to prevent falling down when the simulation starts.

At Motion Navigator, I can see the links and joints I've created. We can see that though I don't set the joint for each link yet, there is a "J001" joint at the Motion Navigator pane because UG NX4 creates a "fixed joint" automatically when we select "fix the link" during the creation of the link.

Next, I create a revolute joint and set the motion driver for the lever. This step is very important. The point and direction of the joint must be correct i.e. Z-axis should be the axis of rotation.

Then I create the 3D Contact between the cylinder and the block and also between the lever and the cylinder.

Then we're ready to start simulation. But we have to make sure that the solver environment is "Dynamics" not "Kinematics" because I would like to see the effect of 3D contact. (Click at the calculator icon).

Next, start motion simulation by clicking at "Animation" and set time = 1 and step = 100 and see the result.

Watch the following video for the result.

Recommended articles related to Unigraphics NX Motion Simulation

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