E5 Lab 3
Testing with SolidWorks

Seating Arrangement:

To facilitate teamwork later in the lab, start with the following seating arrangements

Fα - Dulin            
Fα - Emery Early - FΩ Gα - Karol Lee - GΩ Hα - Thielstrom Robinson - HΩ Gα - Noomah
Fα - Holcomb Brown - FΩ Gα - Landis McGuire - GΩ Hα - Wilson  Pekerti - HΩ Hα - Sacks
Door Front of Room


Jα - Chen            
Jα - Bledsoe  Gelles - JΩ Kα - Ortiz  Alto - KΩ Lα - Thum  Garibay - LΩ
Jα - Gluck Rigell - JΩ Kα - Pitts Liebert - KΩ Lα - Quevedo Redelmeier - LΩ  
Door Front of Room

Pα - Drubin            
Pα - Barron Alhessi - PΩ Qα - Lin Guarini - QΩ Rα - Swartz  Norling-Ruggle - RΩ Rα - Thompson
Pα - Lu Hirsch - PΩ Qα - Heppe Ranshous - QΩ Rα - Friske   Sun - RΩ  
Door Front of Room



The goal of this lab is to use SolidWorks to design (and test) a part that will later be used as an arm for a robot so that it is strong but light.  As you iterate on your design, you will use the results of the SolidWorks tests to figure out  where you should take away or add material to make your arm stronger, while minimizing weight.

  1. This first step in this lab is to be done individually.  Follow directions (details below) to construct (with SolidWorks) and test a robot arm.  Use the results to determine the score for the arm.  You have 40 minutes for this.
    1. First lab period should work individually until 9:10.
    2. Second lab period should work individually until 10:35.
    3. Third lab period should work individually until 12:00.
  2. The next step is to join up in small "squads" of two or three members.  To find what squad you are on, look at the seating chart above.  Your name has two letters next to it, one latin (this indicates your team, F-R) and one greek (this indicates your squad within the group either alpha (α) or omega (Ω)).  The people in your squad have both letters the same as yours (e.g., FΩ or Qα).

    As a squad, look at the results from step 1 and quickly explain your designs to one another.   From your experience working alone, try to come up with a set of guidelines for optimizing your design.  Next start from a clean slate and make a new design, hopefully obtaining a better score than the arm from part one.  Discuss before diving in to the work - try to get input from everybody in the squad.  You have at least 25 minutes to do this, so you will be able to iterate on your design once or twice.  Before getting together as a team, record your squad's best score.
    Important: Save this design and score you will need it for the writeup.
    1. First lab period should work as squads until 9:35
    2. Second lab period should work as squads until 11:00.
    3. Third lab period should work as squads until 12:25.
  3. Important: Make sure each squad saves their best design and score from the previous part as you will need it for the writeup.
    After your squad has come up with its design, get together as a whole team (teams listed on wiki) to discuss the two designs (that of  α-squad and that of Ω-squad) and discuss what approach you will take, as a team, for your final design - try to get input from everybody on the team.  Develop a set of guidelines to use as you iterate to achieve an optimal design.  You have until next Thursday to submit your best design to me - expect to work for one or two hours as a team during the week.  The goal is to get the best design from the team - there should not be one or two individuals dominating..

    As your design improves, record your best score on the wiki in the "Scores" section.  Since teams will be working simultaneously, make sure you save the wiki page, so others can edit it.  This will allow teams to see how good their design is.

    Important: As a group don't forget to put the letter on the circular disk at the end of the arm.  This will be used to distinguish the arms from the different groups after manufacture.

Don't worry too much about having the best score.  The goal of this lab (in addition to a good design) is to be deliberate about your process of figuring out how to optimize your design while working effectively as a group.

To turn in:

(via moodle)

Due next Thursday, 9/24.


Designing, Testing and Scoring a Robot Arm Design

Design a robot arm

Let's design a robot arm according to the guidelines.

Start by downloading the file "RobotArmTemplate.SLDPRT," then "Save As" to your student folder with a unique file name (make sure you don't save it on the local machine, or the file may be deleted after you log off).  Your SolidWorks window should look similar to the one below.   Note the large pink block; this is the material you are allowed to remove.  There are two notches cut into the block that will require you to be more creative in your solution.

The first thing to do is to identify the design with your group.  Edit the image associated with the "GroupLetter" feature, then right-click the text (the pointer changes to  when it is over the sketch text) as shown below.


Now select Properties and change the letter associated with your group.  In this example I will change it to "Z."

Now let's cut away part of the face.  Choose "Top" view, and then click on the face of the template (it should turn dark green).  To add a circular cutaway centered vertically on the face first draw a centerline (select  from the from the sketch menu) and draw a centerline horizontally from one edge of the block to another.  An orange dot will appear when you are at the midpoint of the drawing:

Now use the circle tool from the sketch menu to add a circle whose center is at the midpoint of the centerline you just drew (again, a red marker appears when you are at the midpoint) - the exact size isn't important.  Hit the green check mark to accept the circle as drawn.


Now select cut-extrude from the features menu and for direction 1, choose "Through All."  Hit the green check mark to perform the cut.

Let's now add a few more features, but lets have them symmetric around the center.  Again, select the front face and draw a centerline up through the middle.  Select this centerline and then go to Tools→Sketch Tools→Dynamic Mirror.  Now everything we draw will be symmetric about the centerline.

Draw a circle centered on the large circle.  When it is drawn, its symmetric partner should appear.  Hit the green check mark to accept the circles. 

Note, it is also possible to do this after the fact by selecting an object, and going to Tools->Sketch Tools->Mirror and choosing a sketch and a mirror line.

Before quitting, let's get rid of some of the material to the sides of the centerline.  Choose the line tools and draw a contour like the one below.  Make sure that the last point ends up at exactly the same spot as the first point so you get a closed contour.  Exact measurements aren't important. Next, perform an extruded cut.


Now, do an Extruded Cut through all.

Before continuing, measure the volume of the arm.  Go to Tools→Mass Properties.


 In this case the design has a volume of 0.92 in³ (this is in the allowable range of 0.98 and 0.20 in³).  This will be used to calculate the score.

Important: As a group don't forget to put the letter on the circular disk at the end of the arm.  This will be used to distinguish the arms from the different groups after printing.

Test the robot arm

Now let's test the arm to see how much it deflects under load.  Go to Tools→SimulationXpress.  A toolbar should appear on the right.  On the "Welcome" page, select "Start Over" and then "Next."  The "Fixtures" tag should be highlighted. We must now specify how the arm is to be restrained. Click "Add a fixture" and select the inside of the hub attachment (the piece on the left with your group letter on it) - this fixes that element in space. It is easiest to select them from a trimetric view. The small green arrows indicate that the surface is constrained from motion.  Hit the check mark in the left pane to accept the constraint. It is important that you select this particular surface as the constraint so that all groups' results can be compared to each other.

Hit "Next" and then "Add a force".  Select the feature labeled "Divot1" neat the hexagonal hole at the end.  Note: this is on the same side as the deeper notch in the side of the original arm (and the text on the disk at the other end should be upright).  Make sure the force is 1 Newton (in the left pane of the window) and then hit the green arrow to accept the load.  Right click on the image below and select "View image" or "Open image in new tab" to see a full sized image.

Hit "Next" and then for a material pick the "Plastics" folder and then select "ABS" as the plastic type.  Hit "Apply" to select the material.  This is important:  If you don't pick the correct material your results will be meaningless.

Hit "Next" again, and then "Run Simulation."   After a few seconds a simulation of your arm bending will result.  Under the question "Does the part deform as you expected?", select "Yes, continue".

Now select "Show von Mises stress"

Stress is a measure of the localized forces in the design.  In this image, the maximum stress is shown in red around the large notch and the disk.  Relatively high stresses exist in the lower part of the arm near the disk, and low stresses exist near the top edge and the end of the arm with the hexagonal hole.  The maximum stress is shown at the top of the scale (1,658,373 N/m²).

You can also hit "Show Displacement" to get an image like the one below.

This shows that the greatest displacements (or movements) are near the applied force (which seems obvious, but is a good sanity check).  Looking at the scale on the right, you can see that the greatest displacement is 0.28 mm.  This will be use to calculate the score (below).  Note that the displacements in the diagram are exaggerated by a factor of 53.4 to make them easier to see.

Scoring the robot arm

To score the arm we will multiply the volume by the maximum deflection.  The surface area was 0.92  in³, and the deflection was 0.2821 mm, so the score for this robot arm is 0.259 mm-in³.  (Don't worry about the units) You should  be able to get a better score.

You should stop here and try some designs of your own.  When you get together in larger groups you might want to consider some of the techniques listed below.

Other things to try:

Here are some methods for defining sketches and entities that you may find useful.  Three are described briefly below.

Offset entities

You can create a sketch that follows the contours of another sketch.  As an example consider the design from above.  Create a new sketch (using the sketch menu at the top of the screen), choose the front face of the bar, and then select a segment of the edge of the bar.


Right click on the selected segment and choose "Select Loop."  This should select the outer edge of the body (it may take several seconds).

Now select "Offset Entities" from the sketch menu.  The result is shown below for a distance of 0.03 inches.  I also had to "Reverse" the direction of the offset.  A new sketch has been created that is offset by 0.03 inches from the outline chosen.

An extruded cut of 0.1" will make the bar thinner except around the edge.

I made a similar cut on the other side of the arm.


You can make a complicated shape by overlapping simpler shapes and then trimming the parts you don't want.  For instance, to draw an eye shape, start with three circles:

Now pick "Trim Entities" from the sketch menu and select the parts of the sketch that you want to remove.  Here's the result after an extruded cut.

Thin Sections

You can also create a shape from a closed curve (this is like making the curve and doing the offset, but it is done in one step.  For instance to make a hexagonal donut shape you can create a hexagon (using the polygon tool in the sketch menu).

and then from the features menu choose "Extruded Boss/Base" and select "Thin Feature"


In this case there is an offset of 0.03 in inside the hexagon, and 0.05" outside the hexagon and extruded it 0.1".  Note that since there was already an extruded cut of 0.1" an extrusion simply brings the object to its original thickness and so is OK for this project.  An extrusion of more than 0.1" would extend beyond the original thickness of the robot arm and is disallowed by the design rules.

The final design

The other side is the mirror image, with the exception of the hexagonal shape.

Maximum stress is about three times higher than before.

Maximum displacement is 0.62 mm (scale not shown), higher than before.

Volume= in³ is less than half of the original mode.  But score is calculated with volume = 0.43, displacement = 0.62, score = 0.27 (worse than before)