15-394 Assignment 1: Model A Complex Mechanism

Instructions

In this assignment you will choose a complex mechanism to model, producing both a SolidWorks simulation and a physical embodiment.

Visit the 507 Movements web site. A good collection of suitable mechanisms can be found between numbers 90 and 140. Here's a direct link to the start of the good stuff.

You don't have to stop at number 140; there are some good mechanisms further along as well, e.g., 222 and 223.

You can also find an extensive collection of mechanism animations at Thang's Best Animations. Pick a mechanism that's not too simple (numbers 138 and 164 are example of ones that are too simple).

Model the mechanism in SolidWorks and produce a rendering and a Motion Study animation. To save an animation, To click on the Save Animation button which is in the same row as the Motor, Damper, and Solid Body Contact buttons, but further to the left. Use the MP4 file format. Turn off "fixed aspect ratio" and set the resolution to something modest like 500x500. Note: Use the Intel codec for file compression, not the default Microsoft codec. Be careful not to make the file size too big; keep it below 40 MB.

Simulate

  • Simulate your automaton in SolidWorks. Remember to turn on SolidWorks Motion in the SolidWorks Add-Ins tab, and then change the animation type from "Animation" to "Motion Study".
  • Save an animation file from your simulation. To do this, click on the Save Animation button which is in the same row as the Motor, Damper, and Solid Body Contact buttons, but further to the left. Use the AVI file format.

Make a Drawing

  1. Do File New and create a new Drawing (not Part or Assembly) document.

  2. Make sure the units (bottom left corner of the screen) are IPS (inches/pounds/seconds) and not MMGS or Custom.

  3. Set the sheet size to "custom" and enter 12 inches by 12 inches as the width and height, then click "OK".

  4. Insert a part onto your drawing. Remember to hit Escape to cancel insertion of additional views of the part. In the properties manager, set the part to use sheet scaling, not custom scaling.

  5. If your part has circular holes that show up with centerlines (cross shapes) in the drawing, click on and delete the centerlines.

  6. In the Feature Manager Tree, right click on Sheet1 and select Properties. Verify that the sheet scaling is 1:1; somtimes it defaults to 2:1.

  7. Lay out all your pieces on this one sheet.

  8. Save your file as a SolidWorks drawing file. This is important in case you want to go back and edit any of the individual parts; the drawing file will automatically update, but a DXF file will not.

Make a DXF File

  1. Once you've created your drawing file, choose "Save As" and save the file again as a DXF file.

  2. Run Inkscape, set the file type to DXF (it always defaults to DWG), and open the DXF file. Turn off the "Use A4 scaling" and set the scale factor to 25.4 to convert from inches to mm. Zoom out and you may see a "SolidWorks Educational Edition" banner in the bottom left corner. Click on the banner lines and hit Delete to remove them. (If running on a MacBook you will need to press function-Delete.) Then type control-A to select everything, and set the color to blue.

  3. Hit Escape to deselect everything. Then click and drag to select any internal shapes that should be cut first (such as the little holes in your gears), and set their color to red. If nesting one gear inside another, choose another color, such as green, for that. The idea is to be able to cut shapes from the innermost outward, because when a piece of plastic is separated from the sheet it can drop slightly and thus fall out of alignment with the laser.

  4. Select "Save As" in InkScape and set the file type to "Desktop Cutting Plotter (AutoCAD DXF R14)". Click "Save", then set the base units to "mm" and click "OK".

Fabricate and Assemble

  • Laser cut your parts using some combination of Masonite/hardboard and carddboard.

  • Use the brass round-headed fasteners to attach the components.
  • For the artistically inclined: color your components by painting them, drawing on them, applying stickers or decals, etc.
How to render your assembly:

  1. Assign materials to your parts. To do this, open each part file and, in the feature manager tree, right click on Materials. You can either choose one of the popular materials listed in the pop-up menu, or choose Edit Material for a wider range of choices.

  2. Go back the assembly and verify that your parts are colored correctly. You may need to remove an existing appearance attribute in order to see the material's color. To do that, click on the part, click on the beach ball (Appearances icon), and click on the red X to remove any unwanted appearance attributes. For materials such as plastic you may want to assign a color if the default color is not what you want.

  3. Go to the View pulldown menu and select the Display menu; turn on RealView Graphics.

  4. To eliminate floor reflections and shadows, select the Appearances tab in the task pane along the left edge of the display (this is the same pane where the Feature Manager tree or Configuration Manager tree appears), select the "Screen, Lights, and Cameras" submenu, right click on the Scene entry, and uncheck the boxes for Floor Shadows and, if present, Floor Reflection.

  5. Go to the File pulldown menu, select Save As, set the file type to PNG, and save the image.

Fabricate the mechanism from laser-cut MDF (hardboard) and demonstrate that it works.

Post your rendering and photograph to Canvas in the discussion thread provided.

Hand-In

Hand in a zip file handin.zip in Canvas containing the following:
  1. A text file explaining what mechanism you chose, and what adaptations (if any) you had to make.
  2. Your SolidWorks part and assembly files.
  3. Your animation file.
  4. Your rendering image.
Due date: check the class schedule.

Grading (20 pts)

  • 12 points: SolidWorks model and animation.
  • 4 points: lasercut parts and working model with picture on Piazza.
  • 4 points: Writeup describing the mechanism simulated, and a rendering image.
Dave Touretzky