Structural Systems

Two major systems of every robot on the planet are the structures and mechanical systems. Structural systems allow the machines and buildings to hold themselves together and up off of the ground. Listed below are some of the more common structural systems that teams use in FRC.

Structures

In FRC there are two major off the shelf structural systems; versa frame and aluminum slotted framing. Many teams will use one or both of these structural systems because they require a minimum amount of fabrication knowledge and access to tools. Here are some details about each of these basic structural systems;

  • Versa frame
    • Versa frame comes pre-drilled 5/32 holes
    • Versa frame comes in a variety of shapes and lengths
    • Versa frame has a wide variety of brackets to allow for joining pieces
    • Versa frame has scribe lines to help with drilling additional holes on center
    • Versa frame can easily be pared with West Coast Drive mechanical system components
    • Versa frame can easily be paired with Vex Pro mechanical system components
    • Versa frame is moderately expensive
    • Versa frame is heavy
      • Team’s can drill lightening holes in 1″ x 2″ frame components
  • Aluminum slotted framing (referred to as 80/20)
    • Slotted frame comes formed with a variety of profiles
      • Profiles are the cross section of the extrusion
    • Slotted frame profiles work with a variety of fasteners
    • Slotted frame has a wide variety of brackets to allow for joining pieces
    • Slotted frame has scribe lines to help with drilling additional holes on center
    • Slotted frame can easily be pared with 80/20 mechanical system components
    • Slotted frame is heavy

 

All of the other structural systems should be considered custom solutions. Custom solutions may require more in house fabrication skill and knowledge than most teams have. They may also require some specialized tooling. Here are some of the more popular custom solutions in FRC;

  • Fastened or welded tube
    • Square tube (tube with no pre drilled holes)
      square

      • Weight based on material
        • Carbon tubes – light
        • Fiber glass tubes – light
        • Aluminum tubes – moderately heavy
      • Easy to work with
      • Lots of standardized brackets available
      • Need to be able to precisely drill holes
      • Can be welded or joined mechanically
    • Rectangular tube (tube with no pre drilled holes)
      rectanle

      • Weight based on material
        • Carbon tubes – light
        • Fiber glass tubes – light
        • Aluminum tubes – moderately heavy
      • Easy to work with
      • Lots of standardized brackets available
      • Need to be able to precisely drill holes
      • Lightening patterns can be custom machined
      • Can be welded or joined mechanically
    • Circular tube
      round tube

      • Weight based on material
        • Carbon tubes – light
        • Fiber glass tubes – light
        • PVC tube – heavy
        • Copper tube – heavy
        • Aluminum tubes – moderately heavy
      • Need special tools for bending
      • Need special tools for crimping
      • Moderately hard to source brackets
      • Can be welded or joined mechanically
      • Need radius blocks for fastening
      • Need to be able to precisely drill holes
        • Some suppliers do have tube with pre drilled holes available
  • Bent sheet metal
    sheetmetal

    • Usually joined with rivets and bolts
    • Light weight
    • Need to create CAD
    • Need to be able to create flat patterns
    • Need to be able to manage CAM package
    • Need to be able to precisely drill holes
    • Need to be able to cut sheet metal precisely
    • Need to be able to bend sheet metal precisely
    • Need to be able to accommodate spring back
  • Machined sheet or block
    • If metal usually joined with rivets and bolts
      machined

      • Light weight
      • Need to create CAD
      • Need to be able to manage CAM package
      • Need to be able to precisely drill holes
      • Need to be able to cut metal precisely
      • Need access to vertical mill or CNC router
    • If wood usually joined with mortise joint and glue
      wood

      • Light weight
      • Easy to work with
      • Need to create CAD
      • Need to be able to manage CAM package
      • Need to be able to precisely drill holes
      • Need to be able to cut wood precisely
      • Need access to vertical mill, CNC router or laser
      • Need to be able to clamp and glue wood precisely
  • 3D printing
    3dprint

    • Light weight
    • Need to create CAD
    • Need to be able to manage CAM package
    • Need to be able to model supports

 

Fixed Joints

To avoid high material costs and the need for large scale 5-axis CNC mills most teams will need to design their structure so that it can be easily manufactured with the tools or sponsors they have. This usually results in a structural system that will require many fixed joints. Fixed joins are joints that resist motion along and around all three axis. Check out our page on free body diagrams to learn more about how motion along and around all three axis can be understood. And then check out the page on welding, fasteners and adhesives to lean more about how to create a light weight fixed joint.

 

Structural System Design

Structural Systems need to be able to withstand the expected structural loads over an expected number of cycles. Teams will need to follow these steps necessary to design their structural system.

  1. Sketch out a idea
  2. Build prototypes
  3. Refine the sketch
  4. Refine the prototype
  5. Create a free body diagram
  6. Understand the loads
    1. Understand ultimate load case for each type of loading
    2. Understand the number of cycles for each load case
    3. Do the math
  7. Select materials that can resist the loads
  8. Define the shape that will resist fatigue and is manufacturable

Note – steps 3 and 4 may need to be repeated many times to find the right combination to reduce weight and fabrication complexity

 

Additional Resources

 

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