Your First Tube
Stage 1A · Part Modeling — Model a real length of 2x1 box tubing in Fusion 360
Every Robot Is Tubes
2x1 box tube is the FRC skeleton.
- Drivetrain rails, arms, elevators, bumpers.
- Lightweight 6061-T6 aluminum, easy to machine.
- Bolt patterns on a 0.5in or 1in grid.
- Master this and you can build anything.
Open a real robot CAD or show a photo of a drivetrain. Point out that nearly every structural member is 2x1 tube. Tell them: today's tube is a building block they'll reuse in every future lesson. Emphasize this is THE foundational skill.
Real Tube Dimensions
2x1 means 2.0in x 1.0in outside.
- Standard FRC wall: 1/16in (0.0625in).
- Some teams use 1/8in (0.125in) wall.
- Also common: 1x1 tube, same workflow.
- Sold by VEXpro, WCP, TheThriftyBot, AndyMark.
Clarify: 2x1 is the OUTSIDE dimension, not the hole. Stock FRC tube is usually 1/16in wall to save weight; 1/8in is heavier but stronger for high-load parts. We'll model 1/8in (0.125in) today because it's a clean number and matches the frcdesign lesson. Mention tube comes in long sticks teams cut to length.
New Component First
Right-click top of browser > New Component.
- Name it Tube_2x1 right away.
- Activate it (radio dot filled in).
- Set units to inch: Document Settings.
- Never sketch loose in the root.
This is the #1 habit to drill: always make a component before modeling. Bodies in the root get messy fast and can't be jointed cleanly later. Show how the active component is bolded with a filled dot. Set units to inches now so nobody types mm by accident.
Sketch The Profile
Create Sketch, pick the Front plane.
- Draw a 2-Point Rectangle near origin.
- Dimension it: 2.0in wide, 1.0in tall.
- Constrain one corner to the origin point.
- Sketch turns black = fully constrained.
Pick a plane and have them draw a rough rectangle first, THEN dimension. Use the D key for sketch dimension. Stress fully-constrained = black lines; blue means under-defined. Common mistake: drawing the rectangle far from origin and not anchoring it, so it floats. Lock a corner to origin.
Extrude To Length
Finish Sketch, then press E to Extrude.
- Select the rectangle profile.
- Type the length, e.g. 16in.
- Operation = New Body.
- You now have a solid 2x1 bar.
E is the hotkey for Extrude. Length is your call: 16in is a realistic drivetrain rail. Tell them the length will become a User Parameter later so it's easy to change. Right now it's a SOLID bar, not hollow yet. That's the next step.
Solid bar now. Hollow tube next.
Real box tube is a thin shell — Shell removes the inside and leaves the walls.
Shell The Walls
Modify > Shell.
- Select BOTH end faces of the bar.
- Set Inside Thickness to 0.125in.
- Click OK — bar becomes a hollow tube.
- Direction = Inside keeps outer size 2x1.
Select the two END faces so both ends open up like real tube stock. Inside thickness keeps the outside at 2x1 — if you shell to the outside, your tube grows to 2.25x1.25 and won't fit anything. Common mistake: only selecting one face, leaving one end capped. Walk around and check.
Drive Length With A Parameter
Modify > Change Parameters.
- Add User Parameter: tube_length = 16in.
- Edit the Extrude, type tube_length.
- Change one number, tube updates.
- This is Fusion's version of Variables.
This is the Fusion equivalent of Onshape Variables. Show editing tube_length to 24in and watching the tube grow instantly. Tell them parametric design is why CAD beats drawing on paper: change a spec once, everything downstream follows. Optional but a great habit early.
Verify Your Tube
Inspect > Measure the wall thickness.
- Wall should read 0.125in everywhere.
- Outside must stay 2.000 x 1.000in.
- Both ends open, no caps.
- Check Physical Material = Aluminum 6061.
Teach them to verify, not assume. Use Inspect > Measure to confirm the wall and outside dims. Assign 6061 aluminum under Modify > Physical Material so the mass is realistic — useful later for weight budgets. A wrong wall (e.g. 0.25in) is the most common silent error.
Your Task
- New component named Tube_2x1.
- 16in long, 2x1 outside, 1/8in wall.
- Both ends open, fully constrained sketch.
- Bonus: drive length with a parameter.
- Save the file in Fusion.
- File > Share > Public Link.
- Copy the link.
- Paste it on AltHub board.
Give them 15-20 minutes. Circulate and check: component made? both ends open? wall 0.125? Encourage the parameter bonus for faster students. Remind them to actually Save before sharing — an unsaved file gives a dead link.
Common Mistakes
Forgot to make a component first.
- Shelled to outside — tube grew past 2x1.
- Only one end open (one face selected).
- Sketch left blue / under-constrained.
- Units in mm instead of inches.
Run through these as a checklist. These five account for almost every problem you'll see today. If a tube 'looks fine' but measures 2.25 wide, they shelled outward. If the sketch jumps when dragged, it's under-constrained. Catch units early — a 16mm tube is comically tiny.
🧰 Add-ins for this step
Use the installed AltSkripts / FRC-COTS tools here — don't do it the slow way.
- FRC Tube Extruder — Solid ▸ Create ▸ AltSkripts builds this walled tube with its hole pattern in one step.
- Tubify Solid — or model a solid block first, then convert it to a tube.
You Modeled A Tube Next: Holes & Patterns
- Component > Sketch > Extrude > Shell.
- 2x1 outside, 1/8in wall, both ends open.
- Parameters make length editable in one click.
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.