Box Frame
Stage 1A · Part Modeling — Build a parametric rectangular tube frame in Fusion 360
The Frame Is Everything
Every FRC robot starts with a tube box frame.
- Holds the drivetrain, electronics, and superstructure.
- 2x1 aluminum tube is the team standard.
- Get this parametric and reuse it all season.
Open with a photo of last year's robot. Point out the rectangular base frame made of 2x1 tube. Tell them: today they build the skeleton everything else bolts onto. Stress that 'parametric' means we can resize the whole frame by changing one number later — that's the superpower we're building toward.
Components Vs Bodies
In Fusion, every tube is its own Component.
- Right-click top of browser > New Component.
- Components can be Joined later; bodies cannot.
- Name them: Tube_Front, Tube_Left, etc.
This is the #1 thing Onshape converts get wrong. In Onshape everything lives in one Part Studio; in Fusion we make each tube a separate Component so we can Joint them. Demo creating a component and activating it (the dot lights up). Tell them: if the dot isn't on your component, you're modeling in the wrong place.
Drive It With Numbers
Modify > Change Parameters before you sketch.
- Add frameLength = 28 in, frameWidth = 24 in.
- Add tubeWidth = 2 in, tubeHeight = 1 in.
- Type the name in any dimension to reference it.
This replaces Onshape Variables. Add parameters FIRST so the sketch references them from the start. Show that typing 'frameLength' into a dimension box turns it green/linked. Common mistake: hard-typing 28 instead of the parameter name — then resizing later breaks everything. wallThickness 1/16 in is real 2x1 stock.
Sketch The Tube Section
Sketch a 2 in x 1 in rectangle on a plane.
- Dimension width = tubeWidth, height = tubeHeight.
- Use Offset (0.0625 in) for the hollow wall.
- Extrude to frameLength for the long tubes.
Demo Sketch > Rectangle, then dimension both sides to the parameters. Use Offset (O) to create the wall so it's a real hollow tube, not a solid bar — solid tubes look fine but weigh 3x. Extrude the profile to frameLength. Remind them real 2x1 is 2.000 x 1.000 with a 1/16 wall.
Make All Four Tubes
Two long rails at frameLength, two at frameWidth.
- Model each inside its own component.
- Or copy a component and edit its extrude length.
- Keep the lengths driven by parameters.
Two common build orders: model each tube fresh, or model one and Copy/Paste the component then change its length parameter. Either works. Don't worry about position yet — they'll be scattered in space. Tell them that's expected; Joints fix it next.
JOINTS, NOT MATES. FUSION SNAPS PARTS TOGETHER.
Onshape 'Mates' are Fusion 'Joints' — Assemble > Joint. Rigid for a welded frame.
Assemble The Box
Assemble > Joint, pick two corner faces.
- Choose Rigid joint type for a fixed frame.
- Snap each rail end to the mating rail face.
- Ground one tube so the frame stays put.
Demo grounding the first tube (right-click > Ground) so it's the anchor. Then Joint each remaining tube to it. Use Rigid. Watch for the joint origin snapping to face centers — they may need to pick edge midpoints or use the 'between two faces' option. Mistake: forgetting to ground, so the whole frame drifts when they drag it.
Drill For Gussets
Gussets bolt corners with a standard hole grid.
- Use Hole feature, 0.196 in for #10 hardware.
- Space holes on the 1 in / 0.5 in WCP pattern.
- Match holes across both mating tubes.
Real FRC frames use gussets (WCP/AndyMark) bolted with #10-32 hardware — 0.196 in clearance hole. Emphasize the holes MUST line up on both tubes or the gusset won't bolt on. Use Rectangular Pattern to repeat the holes. This is where parametric pays off: hole spacing can reference a parameter too.
Drop In A Gusset
Insert > Insert McMaster-Carr or upload STEP.
- Grab gussets from WCP, REV, or AndyMark sites.
- Insert > Insert Derive / Insert Mesh for F3D.
- Joint the gusset onto the corner holes.
This replaces Onshape's MKCad library. Vendors ship STEP/F3D files — download and Insert > Insert STEP, or use the built-in McMaster-Carr browser for hardware. Joint the gusset to the corner. Don't model parts you can download — real teams insert vendor CAD to save hours.
Frame Ground Rules
- 2x1 tube, 1/16 in wall
- #10-32 gusset hardware
- 0.196 in clearance holes
- 1 in / 0.5 in hole grid
- Drive sizes from parameters
- Each tube = own component
- Rigid joints at corners
- Ground one anchor tube
Use this as a checklist before they submit. Walk the room and verify each frame uses parameters (not hard numbers), separate components, and rigid joints. If they hard-typed dimensions, make them redo it — the next lesson resizes this frame and it must flex.
Your Task
- A 28 x 24 in box frame in 2x1
- All four tubes as components
- Rigid joints, one grounded
- Gusset hole pattern on corners
- File > Save your design
- Share > Public Link in Fusion
- Copy the generated link
- Paste it on AltHub
Give them 30-40 minutes. Walk around. The two failure modes: (1) modeled as bodies not components, so they can't joint; (2) hard-typed dimensions. Both must be fixed before submission. Remind them Fusion Share > Public Link is how we review — no link, no grade. Test the link in incognito before pasting.
🧰 Add-ins for this step
Use the installed AltSkripts / FRC-COTS tools here — don't do it the slow way.
- FRC Tube Extruder / Tubify — for every box-frame member.
You Built The Skeleton Next: Resize It In One Click
- Components + Rigid Joints = an assembled frame.
- Parameters mean the whole frame is editable.
- Gusset holes must align across both tubes.
Your Task
- Model what this lesson covers in Fusion 360.
- Use the AltSkripts tools where they apply.
- Save it with a clear name.
- In Fusion: Share → Public Link → Copy.
- Paste the link below.
- A coach reviews it in AltHub.