Designing a Robot Arm

See bottom of document for a description of what needs to be turned in for this lab.

Seating Arrangement:

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

Windows Lab Section A (8:30-9:45) Lobby
Front of Classroom
Hernandez Aisle Barry Blakeslee Aisle Luciano - Aisle - Jobson Aisle Meyer-Lee
Arth Veron Kyaw Miller - - Oh Wojciehowski
Gilchrist Nguyen
Back of Classroom


Windows Lab Section B (9:55-11:10) Lobby
Front of Classroom
Dwass Aisle Thompson - Aisle - - Aisle - Norling-Ruggles Aisle Wilson
Johnston Pangelinan - - - - Wang Namjilsuren
Back of Classroom
Windows Lab Section C (11:20-12:35) Lobby
Front of Classroom
Bley Aisle Rittenhouse - Aisle - Luo Aisle Yang Smith Aisle Roberts
Hilburn Lomelli - - Shmoys Watson Small Vik
Back of Classroom


Some Review and Some New Ideas


This toolbar is at the top of the window and allows you to change the view of the part.
Tip! Hold down the scroll button on the mouse to change the orientation of your part.

Features Tab

The Features tab has all the tools that will build on to your part

Raising Features

These features will add raised components to your part. Extruded Boss/Base is what was used to create the cylinder that was the base for the Neopixel Shield.

Cutting Features

These features will cut away from your part


The Fillet feature creates curved edges.



The Chamfer feature can be found under the Fillet pulldown menu and it also alters edges but it is less smooth.

This can be used to Create references (planes, points, lines) to add features


Sketch Tab

The Sketch tab has the tools that will add sketches (2D) to your part, which are used to build features


Often you will use some sort of shape to create your sketches. Check the pull down menus associated with each shape to get the one you want.


Smart Dimension

Smart Dimension can be used to change dimensions after you have created shapes or features. If the feature has already been built, you may have to use the "rebuild" option

Rebuild button, found on the very top toolbar

Designing the Robot Arm

You are to design a Robot that will hold a laser pointer, and also withstand an applied force. The goal of this design is to use SolidWorks to create the strongest arm possible with minimized weight. You will use the SolidWorks platform to simulate the arms response to an applied force, and then the model will be printed out and tested. The force be applied to the divot on the opposite side of the part from the the pink square for your letter. To start, Download laser.SLDPRT and open it in SolidWorks.

Only edit the part of the rectangular arm (joining the circular disk at the right to the cylinder at the left) that is magenta. The part is designed to connect to a motor on one (the disk) side and hold the laser on the other side (the laser fits into the cylinder). You can take away from the magenta arm, and you will add your group letter to the magenta square.

Add Text

The first thing you should do it add your group letter to the square. To do this, Click on Extruded Cut then select the pink surface of the square. You can select the Normal to view option to see the surface easier. You should see the Sketch tab open, waiting for you to create a sketch to be extruded.

Select the Text sketch feature (a capital "A" next to the shape options) and type your letter into the text box. You can change the font size by unchecking the box that says "Use document text", then click on the Font button. Under "Height", select Points and choose the font size that will best fill the square with the letter. The image above uses size 26. Click Okay to view your changes, and when you have placed it correctly, click on the green check mark then select Exit Sketch.

Choose a depth of 0.05 inches and click on the green check mark to see your extrusion.

Cut from the Arm

You can make an extrusion from the arm by clicking on the surface from which you want to cut from, and clicking again on Extruded Cut. If you want to cut a circle from the center of the device, you can first add a Center Line (under Line→CenterLine in Shapes) and hover over the center of one side of the arm. Your cursor will light up orange when you are at the center, and you can click and drag the mouse to create the line.

Then select the Circle shape, and hover your mouse near the center of the line, until an orange point shows up to show the midway point. Use this as your circle's origin to create the circle exactly in the center. Then click on the green check mark and Exit Sketch to create your extrusion.

Under Direction 1 can select Through All to cut through the whole arm, or Blind to only cut to a certain distance.

Add Symmetric Features

You may have to add a centerline like you did before. Go to Tools→Sketch Tools→Dynamic Mirror and then select the center line. Now everything we draw will be symmetric about the centerline. You can Exit the Sketch and click on Extruded Cut in the Features toolbar. Then select the shapes that you just drew to cut out.

You can add as many features as you like, by right clicking on the Feature in the feature tree on the left and choosing Edit Feature, then Edit Sketch.

Measure the Volume of the Arm

Before Continuing, measure the volume of the Arm ( Tools→Mass Properties ).

So far, the piece has a volume of 0.59 cubic inches, which will be used to calculate the score.

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 Next, and you will be directed to choose a fixture. The wheel-like disk at the opposite end of the arm from the letter has a circular divot in the middle and four holes for screws. This is where the arm will be fixed and the other side will receive the force. Click on Add a fixture and select the face of the circle. (You can open image to expand it).

The green arrows indicate the direction in which the part is fixed. You can zoom in to see that they are fixed in three directions across the face of the . Hit the green check mark and then Next. Now select Add a force. Add the force to the divot on the opposite side of the laser-holder from the letter that you added. Click on the center of the small circle to add the force. Make sure the force is added as shown below, and that the value is 1 Newton.

Click the green check mark to continue. 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 and then close. This is important: If you don't pick the correct material your results will be meaningless because they won't be comparable to those of others in the class.


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

If your simulation doesn't run it may be because SolidWorks is trying to write the results of the simulation to a folder to which you don't have access. In that case go to Tools→Xpress Products→SimulationXpress. Now on the panel on the right side of the screen pick Options and change "Results Location" to a folder you can write to (the Desktop works).

Now select Show von Mises stress

Stress is a measure of the localized forces in the design. The maximum stress is shown at the top of the scale (3.9mPa = 3,900,00 N/m²), but the corresponding bright red color is not visible from this angle. However, you can see that stresses are high near the corners of the small square cutouts and the outside edges of the circles, and low in the middle of the beam on the side with no cutouts.

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 0.0285 mm. This will be used 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.

Calculate the Score

Rules about calculating the score.. below are copied from previous E5 lab
To score the arm we will multiply the volume by the maximum deflection. The volume was 0.92 in³, and the deflection was 0.0285 mm, so the score for this robot arm is 0.0262 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

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.

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.

Now you can Exit Sketch and create an Extruded cut to the inner line. Here, I chose a distance of 0.1 in.


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, then Trim to Closest 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. I had to reverse the direction of the feature by clicking the arrows under Thin Feature. Note that this element of the design is actually illegal under the rules because we are adding material outside of the original rectangular arm. However, you could follow the same process to make a thin feature using an extruded cut.

Removing More Material

You can also remove more weight by creating extrusions from the other side (the side with the "eye" shown above).To do this, select the plane from which you will be making the cut. Then click Extruded Cut . You will be prompted to create a sketch. Here I chose to make a rectangle.

Click on Exit Sketch. Under "Direction 1" select Through All and then click the green check mark. I also cut out some circles and the center hexagon.

Test the Arm Again

Now try testing the arm again to see how this cut changed your score. Follow the steps above to test your arm. The von Mises stress is shown below. Compared to the last test, there are larger stresses with this design. Note that in these images that the fixtures have been changed to the holes in the circular flange - you should not make this change: keep the fixture as the face of the flange as was done in all of the examples above.

Shown below are the displacements (these displacements are also larger than before due to the material taken away)..

To turn in (next Thursday):