Simple motion study with SolidWorks

Jack K

7 Nov, 2018 06:00 PM

This tutorial introduces a quick and easy way to do a motion study. It just takes a few minutes to draw a stick diagram and add a few dimensions and mates, and then animate the diagram to show how the parts move and interact with each other.

(Of course we could make an assembly of fully detailed parts for a motion study, but that takes more time and more work)

I first learned this technique with CATIA sketches, and it's just as useful with SolidWorks.

1. Step 1: before we start

   
   

   This technique works with 2D mechanisms only. Things like cranks, 4-bar linkages, etc.

   

   

   
   

   But this only works for rigid parts, so no springs!

   
   

   And, this is only motion study. No forces! No friction! No gravity!

2. Step 2: Vice Grip (Locking Pliers)

   

   
   

   
   

   1. Make a new SolidWorks drawing. (you could do this with a sketch instead, but a drawing works a little better) 
   2. Use the sketching tools to draw 4 points (A, B, C, and D) just like the points above
   3. Draw 4 lines between the points, similar to the dashed lines in the picture above. Each line represents a part of the pliers.
   4. Delete line AB, and draw a new, longer line like the one below.
   5. Mate point A coincident to the long line, and mate point B coincident to the long line

   
   

   Here's the drawing so far:

   

   
   

   This is called a "4-Bar Link Mechanism, because there are 4 parts: 

   

   
   

3. Step 3: Add dimensions

   1. Add dimensions to define the lengths of lines BC, CD, and DA.
   2. Add a dimension between points A and B
   3. Make sure the all the dimensions define the true lengths of each line (not the vertical or horizontal lengths)

   

4. Step 4: Add mates

   
   

   
   

   
   

   
   

   1. right-click on point A and make it fixed. 
   2. right-click on point B and make it fixed also. This should also make the top line fixed
   3. verify there are Coincident mates at points C and D by selecting each point individually to see the mate symbols.
   4. check your drawing to verify there are no other mates - just the Fixed and Coincident mates. Delete any other mates you find.

5. Step 5: Put the diagram in motion

   1. Use the mouse to drag point D left and right. This will rotate line AD (lower jaw) about point A
   2. If the line doesn't rotate, there is a mate that is preventing it from moving. Check all the mates and delete the ones that are not needed.
   3.  Drag point C up and down. This will rotate line BC (the link) about point B. Notice the motion is limited based on the lengths of the lines
   4. Modify the lengths of some of the lines. Then drag the points again to see the difference it makes to the motion.

6. Step 6: Add more detail

   To help better understand the mechanism, we can add more detail to our pliers diagram

   
   

   
   

   
   

   1.  Drag point D to the left almost as far as it will go
   2.  Add two lines to form a triangle, and dimension the length of both lines. Be careful to dimension these lines back to points A and D

   
   

   1.  Drag point C to see how the tip of the lower jaw moves
   2.  Add a few more lines and dimensions to represent the teeth on the lower jaw. Check the mates that are added automatically and delete the ones that are not needed

   

   
   

   3. add a line) to represent the lower handle. Dimension this relative to the line CD.

   

   
   

   
   

7. Step 7: Finish the Vice Grip study

   Hide all the dimensions to clean-up the diagram

   Drag the end of the lower handle to see the motion of the pliers

   

   
   

   

   
   

   
   

8. Step 8: the end?

   Hopefully you learned something and can do a simple motion study of another mechanism.

   
   

   Please leave a comment on what you thought of this tutorial. Good?  Difficult to follow?Something you might use in the future? etc. 

   
   

   And click the Thumbs Up if you like it!

   
   

   (I plan to add a crank to this tutorial soon)