CAD & CAM

CAD or Computer Aided Design is one of the most critical things your team can do to become more successful. CAD enables your team to be more efficient and effective with the limited time and financial resources of FRC. CAD at its roots does two things; captures design intent and communicates design intent, thus the more you CAD the more you communicate. Conceptual CAD should be completed within 5 days of kickoff. Prototype CAD should be completed within 7 days of kickoff. Final CAD should be completed within 10 days of kickoff. This rigorous schedule pushes teams to do most of their thinking up front so that they leave as little of their robot design up to chance. When doing CAD teams should think about the following at the following stages;

Conceptual CAD

  • What are the goals / requirements
    • Repairability
    • Ease of assembly
    • Game functions that need to be completed by the robot
    • Game functions that we want to be completed by the robot
    • Game functions that would be nice if the robot could complete
    • Rules
  • Game pieces are modeled and interacted with
  • Field is modeled and interacted with
  • Major structural components are modeled
  • Keep modeling time to under 2 hours per concept

2015 concept1concept 2 image 3

Prototype CAD

  • What are the teams limitations
    • Time
    • Cost
    • Detail part fabrication capability of the team’s students
    • Tools available to the team for fabrication
  • What are the ranges of motion of your mechanisms
  • What are the major and minor assemblies
  • Where will the electronics go
    • Use cubes to represent
  • Where will the pneumatics go
    • Use cubes to represent
  • What is the Master axis system for the robot
  • What are the materials you know you are going to need and can order before detail design is finished

Concept 3 image 4Concept 3 image 4Concept 3 image 1

Final CAD

  • What are the Free Body Diagrams (FBD) for your robot
  • What are the parts you are going to use for every aspect of the robot
    • Who is the supplier
    • Are the parts legal and available
    • How is every part going to be fabricated or sourced
    • What are the materials
  • What is the assembly order for the robot
    • Where are the payoffs
  • What fasteners are used at every joint
  • What gears or sprockets will be used for every mechanism
  • What mechanical transfer mediums are being used
    • What are the belt sizes
    • What are the number of chain links
    • How will they be tensioned
  • Does the math of your mechanisms work with the parts selected
  • What is the weight of the robot
  • Where is the Center of Gravity (CG)
  • Where will every electronic component go
    • Is the batter easily removable
    • Where will the wires go
    • Are the status light easily view able
  • Is the drive system easily repairable
  • Are major mechanisms easily repairable
  • Where will every pneumatic components go
    • Is the full range of motion possible
    • Do you need mechanical stops
  • Do we violate any rules
  • Does it meet all of the teams need level requirements
  • All of the assemblies and detail parts are labeled

Team1389-2015_field-12 Team1389-2015_electrical-1 Team1389-2015_field-13

 

Teams have a large variety of CAD software available to them, for free through FIRST; Autodesk and Solid works are the two most popular. Please see FIRST’s CAD webpage for the details on how to download the software for free. Once you have the software you will need to learn how to use it. Check out these tutorials to learn the basics.

 

Once you know the basics you are ready to learn about how to model detail parts and simple assemblies. But FRC robots can be made out of more than 200 parts and 300 fasteners. When modeling at this scale we recommend that you learn some more of the advanced ways of thinking about CAD;

  • Model based definition
    • This is thinking in terms of models as opposed to drawings.
  • Relational Design
    • This is thinking in terms of how the final assembly, relates to major assemblies, which relate to minor assemblies and how they all relate to detail parts, multi use assemblies and multi use parts
  • Parametric design
    • This is thinking in terms of CAD efficiency
  • Be strategic and minimize what you have to model
    • This is thinking in terms of reuse and reduction of total CAD effort
      • adTown CAD Library – FRC Team 1323, MadTown Robotics
      • 3D Content Central – Host an enormous variety of free CAD models including all components of the FIRST Kit of Parts
      • Autodesk FIRSTbase – Where all Autodesk submissions are made, voted on, and archived. FIRST teams can also download Professional licenses of Autodesk software for free here once registered
  • Product Data Management (PDM)
    • This is how you store CAD data, versions and metadata
    • We use GrabCAD
  • Design for Manufacturability (DFMA)
    • This is thinking in terms of tolerances, tooling, assembly order and payoffs
    • GD&T or FT&A are big parts of DFMA

 

After you finish you robot you will need to purchase or fabricate all of the items on your Bill of Materials (BOM). You may have planned to fabricate several of the parts by hand, making parts by hand is defiantly one way to go, but you need to understand the limitations of this fabrication method often include large tolerance issues for many FRC teams. Tolerances issues translate into assembly slop that could result in misalignment of major structural components or significant amounts of inconsistency when performing tasks. So instead we recommend using parts that are made using Computer Aided Manufacturing (CAM) techniques. There are many CAM options available to teams;

  • CNC routing
  • CNC lathe
  • CNC laser
  • CNC welding
  • CNC water jet
  • 3D prining

 

CNC stands for Computer Numerical Control and 3D printing is a euphemism for additive manufacturing techniques. Both of these types of machines allow teams to focus on making the data that the CNC machine will need to turn raw materials into the parts that you designed. For many machines the team will need to post process the CAD data to make the commands for specific machine they are going to use to fabricate the part. Each CNC or 3D vendor will identify what the post processor software the team will need to use. For CNC routers for example teams will need to identify the x,y,z, zero point, bit size, rpm, cutting paths etc.. so that the part is fabricated correctly once it is placed in the machine. The same type of forethought is needed for 3D printers, where will the machine start to print, will it print just the exterior or fill in in the interior, does it need supports to avoid deformation during printing, etc…

 

The Team is just starting its grab cad and is making all of our CAD available here

There are numerous other teams who also make their CAD available

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