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How to do a Motion Analysis in SolidWorks?

Motion Analysis is one of the 3 types of motion studies that you can perform in SolidWorks. It is the most powerful, sophisticated, and computationally strong of the other types of Motion Studies. It is used to accurately simulate and analyze the motion of an assembly while taking the effects of Motion Study elements such as forces, inertias, springs, dampers, and friction into consideration. Motion Analysis is only available with the SolidWorks Motion add-in from SolidWorks Premium.

Before you start creating a Motion Analysis, there are some things that you need to check in order to get a successful study:

1. Motion Analysis takes account of material properties as well as mass and inertia of the components in the computations. So make sure you have applied materials to all of your parts. Go to Tools -> Evaluate -> Mass properties to check mass, density, and inertia values.

2. Make sure that you do not have redundant mates in your assembly. For Motion Analysis studies, having redundant mates is the equivalent of over-defining a model. Redundant constraints can provide inaccurate motion calculations. If working with linkages, removing redundancies improves the accuracy of the force results. To address this problem, try one or more of the following, in the given order, as appropriate for your model:

  • Create rigid subassemblies and rigid groups for components that are fixed with respect to the assembly motion.
  • Redefine the model such that there are no redundant mates or as few as possible.
  • Identify all the redundant mates and manually change those mates into bushings on the Analysis tab in the Mate PropertyManager.
  • Replace redundant mate pairs that form a hinge with hinge mates. A hinge mate limits the movement between two components to one rotational degree of freedom. It has the same effect as adding a concentric mate plus a coincident mate. You can also limit the angular movement between the two components.
  • Replace redundant mates with mate primitives.
  • Select Replace redundant mates with bushings in the Motion Study Properties PropertyManager. This option significantly slows down the simulation time and may yield erroneous results, so try this only after exhausting other options.

3. Not all mates are supported in Motion Analysis. Make sure that these mates are not present in your assembly:

  • Width mates are not supported.
  • Coincident mates of coordinate systems are not supported.
  • Symmetry mates are supported only if there are only two geometries.

4. Before you can start a Motion Analysis on an Assembly, you need to enable the SolidWorks Motion Add-In. To do that click on the SolidWorks Motion tool present in the SolidWorks Add-Ins toolbar. You can also enable it by clicking on the drop-down icon present alongside the SolidWorks Option icon in the Standard toolbar, then clicking on Add-Ins.

In the Add-Ins dialog box, check SolidWorks Motion and click Ok.

With the above steps performed, you can start the Motion Study by clicking on the Motion Study tab present at the bottom of the screen. After that select the type of simulation you want to perform. There are 3 types of motion simulations available in SolidWorks including Animation, Basic Motion, and Motion Analysis.

This tutorial is focused on Motion Analysis but parts of it can be used when performing Animation or Basic Motion. Change the Motion Type to Motion Analysis. Then, click on the Motion Study Properties icon.

In the PropertyManager, under the Motion Analysis menu, change Frames per second to a low value of 8-10 if you don’t have a high-end processor. (Even if you have a high-end processor we recommend you to keep it down as Solidworks is a single-core software and Motion Analysis requires high computational power.) Check Replace redundant mates with bushings if your model still has redundant mates. Click the Green Checkmark to apply the settings.

Now set how long your motion is gonna last (let’s say 4 seconds). To do that, click and drag the Key-point present along with the name of your assembly to the 4-sec mark. You can change this anytime you want.

Note: If your MotionManager window is not visible as shown in the above images, you may need to expand the MotionManager using the up arrow present in the lower right corner of your screen.

Now let’s set up our Orientation and Camera Views. Orient your model to the position with which you want to start your motion analysis. Now right-click on the Orientation and Camera Views Key-point and click Replace Key.

Now, press Ctrl on your keyboard and click and drag that Key-point to make a copy of that. You can now orient your model in a different way and then right-click on this new key point and select Replace key to replace it with a new view. You will notice that these two key points will now be joined with a solid line. This indicates that there is a transition happening between these key points. SolidWorks will make a smooth transition between these key points.

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Now let’s make a transition to lights. Expand the Lights, Cameras, and Scene to access individual lights. Make sure that the time bar is at 0 sec. (The solid dark gray vertical line on the timeline is the time bar. It represents the current time. See arrow in below image.)  We want to turn all the lights off and then gradually turn them back on. So we are turning all the lights off by right-clicking on each light and selecting Off in SolidWorks. Now we move the time bar to 1 sec and then turn all the lights on.

You can edit your lights as you wish. Instead of turning them off, you can change their color, intensity, position, etc. by right-clicking on them and selecting Properties.

We will stop and show you what the resulting animation looks like as of now, based on the timeline you see in the above image.

Now that you know how to set up and transition the camera views and lights, you can use the same key-point method to do many more things in your motion video such as hide/unhide, move and explode any component, change transparency and appearances, suppress/un-suppress mates and so on. This Key-Point based method can be used in Animation as well as Basic Motion. But what makes Motion analysis different is the various elements that you can use to actually simulate real-world conditions. So let’s dive into the elements of motion analysis.

You can continue with the previous motion study or you can create a new one. To create a new motion study, click on the New Motion Study tool present in the Assembly toolbar or go to Insert -> New Motion Study, or right-click on the Motion Study tab at the bottom and select Create New Motion Study.

Again, don’t forget to set the motion type from Animation to Motion Analysis.

Use the Motion Study elements to model the motion of a component or assembly. There are 6 types of Motion elements available in Motion Analysis.

1. Motors

Motors are used to apply motion (linear/rotary) to a component without consideration of mass or inertia. They move components in a selected direction, but they are not forces. Motor strength does not vary based on component size or mass.

Motion due to motors supersedes motion due to any other motion study element. Any element that tends to resist motor motion increases the power consumption of the motor but does not slow down the motor motion. i.e. if you have a motor moving a component to the left, and a force pulling the component to the right, the component moves to the left, while the power consumption of the motor increases.

So, let’s add a motor to our motion study by clicking on the Motor icon to access more options.

In the Motor Type, select Rotary Motor if you want rotational motion, Linear Motor if you want a linear motion or Path Mate Motor to move a component along a path (you should have a Path mate in the assembly to use this type of motor).

Under the Component/Direction menu, for Rotary motor, select the cylindrical face/axis/circular edge along which the component will rotate, for Linear motor, select a face/edge/line along which the component will move, for Path mate motor, select your path mate that defines the path of motion. A red arrow will appear indicating the motor direction. If required click on the Reverse Direction button to reverse motor direction.

Now define the Motion of the motor.

  • The Constant speed type is used when you want your motor to move at a constant speed.
  • Distance type is used when you want the motor to operate for a set distance and time frame.
  • Oscillating type allows you to specify an oscillating motor profile such as that of a pendulum.

Note: Do not add more than one motor of the same type to the same component.

Click Ok and you will find that a Rotary Motor feature has been added to the Feature Tree of the MotionManager. Again you can use the Key-Point method to turn the motor off/on or increase/decrease its speed. You can right-click on the Rotary Motor feature and select Edit Feature to edit the motor definition.

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Note: When you use Edit Feature, pay extra attention to the time bar because if the time bar is not at 0 sec time and you change your motor properties, SolidWorks will automatically create a new key-point where the time bar is. If there already is a key-point present on the time bar, it gets overwritten with the new one. You can also edit the values of a key point by double-clicking on it.

Below is an example of the Motor element of the Motion Analysis with some camera orientation changes and hiding/unhiding of components to show internal working parts.

Springs

Springs are used to move components around an assembly by simulating the effects of various types of springs. A component with a smaller mass moves faster than a component with a larger mass when acted upon by an equal strength spring. There are 2 types of springs available, linear spring and torsional spring.

Under Spring Type, select Linear Spring if you want to apply a force between two components in a particular direction, or select Torsional Spring if you want to apply a rotational force between two components.

Under the Spring Parameters menu, select the endpoints of the spring and then define the Exponent of Spring Force Expression, Spring Constant (a spring with a higher spring constant moves a component faster than a spring with a lower spring constant), and the Free Length (the spring does not exert any force when its length is equal to its free length) of the spring.

Select Damper to dampen the effects of the spring. Set the Exponent of Damper Force Expression and then define the Damping Constant to apply a damper to the spring.

The Display menu allows you to change coil diameter, wire diameter, and the number of coils for the spring preview. Spring Preview is only visible when Spring PropertyManager is open, or when you calculate/play the study.

Tip: If the Springs (or any of the Motion symbols) are not visible in the motion study, make sure to turn on the Motion Symbol icon present in the Visibility tool of the heads-up display or go to View-> Hide/Show -> Motion Symbols.

Damper

A damper is used to dampen the effects of spring. The Spring element has an inbuilt option for a damper but you can also apply the damper separately using the Damper tool.

Under the Damper Parameters menu, select the endpoints of the damper and then define the Exponent of Damper Force Expression, and then enter the value of Damper Constant (a damper with a lower damper constant moves a component faster than a damper with a higher damper constant).

Force

Using the Force element of Motion Analysis you can apply a linear force or a torque on any component in your assembly.

Select Type depending on whether you want the force or torque to use for the study.

Under the Direction menu, you can select Action Only if you don’t want your component to generate the action force/torque (i.e action-only force/torque acts on a body but is not generated from a body) or select the Action & Reaction in which the reaction body responds with an equal and opposite force/torque.

Next, specify the point of application of the force/torque (it can be a face, edge, or vertex) and then define the direction of the force/torque if needed.

Under the Force function, define the kind of force you need for the motion study. Click Ok and a Force feature will be added to the Motion Manager FeatureTree.

In the below video, all the masses have a constant force of 30N pulling them downwards for 1 second (the blue arrows show the force). All the springs are similar to each other. The only difference is the damper. The first spring does not have a damper so it keeps on oscillating for a long time, the second spring has a higher damper constant than the third one so it retracts more slowly.

Contact

Contact is used to prevent parts from penetrating each other during motion. Normally contact between components is ignored (i.e. components will pass through each other) unless you configure Contact in the motion study.

In the Contact Type, select Solid Bodies if you want to add 3-dimensional contact between moving components or select Curves if you want to add two-dimensional contact between two touching curves.

Check Use contact groups to enable contact group selection. When enabled contact between parts in the group is ignored but contact between all combinations of pairs of components across two groups is considered.

Select the Material checkbox to enable material selection for each contact pair or group of pairs. The material properties that you select are applicable to touching faces during actual contact. It overrides the material properties assigned to each part.

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Deselect the Material checkbox to get access to the Friction menu where you can define custom values for friction. It also allows you to edit the values of Elastic properties.

Tip: If your simulation does not perform as expected, try modifying elastic properties.

Gravity

It is used to add gravity to your assembly. Gravity moves components of an assembly by inserting a simulated gravitational force like in the real world. All components accelerate at the same rate under the effect of gravity regardless of their mass. You can use only one definition of gravity for an assembly.

Under the Gravity Parameters menu, select the direction of gravity. A Green arrow depicting the direction of gravity will be shown at the bottom-right corner in the graphics area. Select Reverse Direction if needed. Then set the desired numeric value of gravity and click Ok.

Tip: Make sure that there is at least one fixed component in your assembly, otherwise, your assembly will keep on going down and down and down…

After setting up all the elements that you require for your Motion Analysis, click on the Calculate button present in the MotionManager Tools.

Note that SolidWorks being a single core application may take some time to calculate the results. If Animate During Simulation is checked in the Motion Study Properties, you can see how your study is going on.

After the calculation is done, click on the Play From Start button to play the assembly from the beginning or click on the Play button to start playing from where the time bar is located. Use the Stop button to stop the playback.

You can also change the playback speed by clicking on the 1x and inputting your custom speed value or just selecting one from the predefined list provided alongside. If needed, use the Playback Mode icon to change the playback mode to Loop or Reciprocate depending on what kind of playback you want.

You can also save your playback to an external file with help of the Save Animation button.

Generally, Mkv or Mp4 is preferred in Save as type to ensure better compatibility and smaller file sizes. Under Image Size and Aspect Ratio you can manually enter the resolution of your video file and also specify the aspect ratio. In the Frames per second box, enter 30 for smooth playback of video or you can enter a higher value for a buttery smooth video. (Since most of the display screens only offer 60Hz, meaning they can only display 60 fps (frames per second), you may not want to save the video with a higher fps than 60.)

The below video uses the Contact and Gravity element of the Motion Analysis to find out which ball reaches the other end first on different types of the ramp.

You can also use Motion Analysis to plot simulation results for further analysis. Click on the Results and Plots button to proceed.

Just for an example, we are going to plot a graph between the x-component of the linear velocity of the ball that completed the race first. So under the Result menu, in the first box, we selected Displacement/Velocity/Acceleration because we want to find the velocity of the ball. In the second box, we selected Linear Velocity, and in the third box, we selected X component. Then select the entity you want to measure the velocity of, it can be a point, edge, or face. In the Component box, select the component to define XYZ directions or you can also leave it empty if not required.

Click Ok and you will be greeted with your graph. If you click on the Play button, you will find a red line moving through the graph to help you better understand the results.

The better your understanding of the physics of the motion you require, the better your results. Having a rough idea of the expected animation and magnitude results is required as this helps validate simulation results for the design.

You can use Motion Analysis to run impact analysis studies to understand the component responses to different types of forces too. But we will leave that for the next tutorial.