1. C omputer A ided D esign Using software for better designs Rob Stehlik, Crescent School (Team 610) rstehlik@crescentschool.org

2. Agenda Which CAD program is best? More than pretty pictures The value of 2D 3D parts and assemblies Design tips Demo: Gearbox design Resources

3. Which CAD program is best? The short answer: Solidworks! Solidworks is fairly easy to use, and quite powerful. It’s also very common in industry. But really it doesn’t matter, just use what you have Learn what your mentors use Both Autodesk Inventor and Solidworks are available free for students involved in FRC

4. More than pretty pictures CAD is a tool for creating designs, not rendering super realistic images

5. The value of 2D You can accomplish a lot with simple 2D sketches -robot layout -mechanism geometry -size constraints Don’t rush to 3D Examples: kicker design bump traverse

6. 3D parts Basic process: make a 2D sketch, then turn it into a 3D part Combining simple features, you can make very complex parts Demo: make a wheel

7. 3D assemblies Once you have a set of parts, you can put them together in an assembly Assemblies help to make sure everything fits together, keep track of weight, create a bill of materials for ordering components The more detailed your assembly, the smoother your build

8. 3D assemblies Keep track of your weight Assign materials to the parts Example: wheel assembly Coyobot VII, team 610 in 2006 Build weight: 142 lbs Regulation weight: 10,000 holes later

9. 3D assemblies Subassemblies help keep things organized, and make changes easier

10. Design Tips Write out all of your requirements Start with a standard material size (check mcmaster carr) Work within your manufacturing capabilities Talk to your machinists! Download 3D models, but if possible measure the real thing

11. Gearbox Design Requirements -single speed gearbox -driven by one CIM motor -50:1 gear ratio -use AndyMark gears

12. Gearbox Design Some terminology and background info: Gears are specified by the pitch, which is the number of teeth per inch The pitch circle is an imaginary circle within the profiles of the teeth of a gear, such that it rotates against a similar circle on a meshing gear So how do we determine the correct centre distance?

13. Gearbox Design Pitch diameter can be calculated by D = N/p Some common AndyMark gear sizes are shown here Let’s choose our gears and design the gearbox! pitch# of teethpitch diameter 20120.6 140.7 150.75 281.4 402 502.5 562.8

14. Resources FIRST CAD library http://www.firstcadlibrary.com/ MadTown robotics CAD library http://team1323.com/cad/index.html MadTown CAD tutorials http://www.team1323.com/pages/cad_tutorials.php FRC Designs http://www.frc-designs.com/index.html