Using software for better designs
Computer Aided Design
Rob Stehlik, Crescent School (Team 610)
rstehlik@crescentschool.org
Agenda
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Which CAD program is best?
More than pretty pictures
The value of 2D
3D parts and assemblies
Design tips
Demo: Gearbox design
Resources
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
More than pretty pictures
• CAD is a tool for creating designs, not rendering super
realistic images
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
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
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
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
3D assemblies
• Subassemblies help keep things
organized, and make changes easier
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
Gearbox Design
Requirements
-single speed gearbox
-driven by one CIM motor
-50:1 gear ratio
-use AndyMark gears
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?
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 diameter
20
12
0.6
14
0.7
15
0.75
28
1.4
40
2
50
2.5
56
2.8
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