c omputer a ided d esign using software for better designs rob stehlik, crescent school (team 610)...
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Computer Aided Design
Using software for better designs
Rob Stehlik, Crescent School (Team 610)[email protected]
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Agenda• Which CAD program is best?• More than pretty pictures• The value of 2D• 3D parts and assemblies• Design tips• Demo: Gearbox design• Resources
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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
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More than pretty pictures• CAD is a tool for creating designs, not rendering super
realistic images
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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 designbump traverse
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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
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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 smootheryour build
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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
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3D assemblies• Subassemblies help keep things
organized, and make changes easier
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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
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Gearbox DesignRequirements
-single speed gearbox-driven by one CIM motor-50:1 gear ratio-use AndyMark gears
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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?
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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 teeth pitch diameter20 12 0.6
14 0.715 0.7528 1.440 250 2.556 2.8
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ResourcesFIRST CAD libraryhttp://www.firstcadlibrary.com/
MadTown robotics CAD libraryhttp://team1323.com/cad/index.html
MadTown CAD tutorialshttp://www.team1323.com/pages/cad_tutorials.php
FRC Designshttp://www.frc-designs.com/index.html