More Tubes
Reusing tube profiles and User Parameters to crank out 2x1 tubes of any length, fast.
One Tube, Many Lengths
A robot is mostly 2x1 tube cut to length.
- Last lesson you modeled one tube the slow way.
- Today: make new lengths in seconds, not minutes.
- Sketch reuse + User Parameters = no rework.
- Change a number, the whole part updates.
Frame the problem: a real FRC drivetrain or superstructure is a dozen pieces of 2x1 and 1x1 tube. You do NOT want to re-sketch a rectangle and re-extrude for every single one. Tell them today is about working smart. Mention frcdesign calls this 'More Tubes' for a reason.
What Is A Tube Profile
- FRC standard: 2x1 0.1in wall aluminum.
- Outer rectangle 2.000in x 1.000in.
- Inner rectangle offset 0.100in inward.
- Extrude the ring to get hollow tube.
- 1x1 and 2x2 are the same idea.
Quick recall of last lesson. Stress that the cross section is a rectangle with an offset rectangle inside (a 'ring'), extruded. The 0.1in wall is the standard VersaFrame / Tube stock wall. Don't let them model a solid bar by accident, that's the #1 beginner mistake.
Change Parameters Dialog
MODIFY > Change Parameters opens the table.
- Click + under User Parameters to add one.
- Name it, give units (in), give a value.
- Names: no spaces, start with a letter.
- Use these names later instead of typing numbers.
This is the Fusion equivalent of Onshape Variables. Demo opening MODIFY > Change Parameters. Add a parameter live. Emphasize naming rules: tubeLength is fine, 'tube length' is not. Tell them units matter, type 'in' so a value of 16 means 16 inches not 16 cm.
Three Parameters To Add
- tubeLength
- tubeWidth
- tubeHeight
- wallThickness
- 16 in (varies per part)
- 2 in
- 1 in
- 0.1 in
Have them type all four into the Change Parameters table before touching the sketch. tubeWidth/tubeHeight describe the 2x1 cross section; wallThickness is the 0.1in stock wall. tubeLength is the one that will change constantly. Tip: keep width/height/wall the SAME across all tubes; only length changes per part.
Type Names Not Numbers
Dimension the rectangle, then type tubeWidth.
- Fusion accepts parameter names in any value box.
- Offset inner rectangle by wallThickness.
- Black sketch dims now reference parameters.
- Edit one parameter, sketch resizes itself.
The core skill. When the dimension box pops up, type the parameter name instead of a number. Show that the dimension turns into 'tubeWidth' and the geometry obeys it. Demo changing tubeWidth from 2 to 1.5 and watch the rectangle shrink. Common mistake: typing the number anyway out of habit.
Extrude By Parameter
- Select the ring profile, press E to extrude.
- In Distance, type tubeLength.
- Set operation to New Body.
- Tube length now lives in one parameter.
- No more remembering 16.25 vs 18.5.
Extrude distance is just another value box, so it takes tubeLength too. Make sure they extrude the RING (the area between the two rectangles), not the inner hole. If they only get a thin frame missing, they selected wrong. New Body keeps it as its own body so they can pattern or component it later.
Change the number, not the model.
With parameters wired in, a new tube length is one edit in the Change Parameters table — the sketch and extrude both update.
Copy Vs New Parameter
Need many different lengths at once? Don't reuse one param.
- Copy the body, then it shares the same length.
- For varied lengths, make tubeLength_A, _B, _C.
- Or model each tube in its own component.
- Each component carries its own parameters.
Clarify a subtlety: one parameter drives one value. If you want five DIFFERENT lengths simultaneously, you either need five parameters or five components. Explain this is why real robots use components per part. Onshape kids might expect 'configurations', tell them in Fusion the clean way is separate components.
Edits Live In The Timeline
- Bottom bar = every feature in order.
- Double-click a sketch to re-edit dimensions.
- Double-click the extrude to change length.
- Drag the end-marker back to time-travel.
- Parameters update everything regardless of order.
Show that the timeline is a history. You can always go back and fix a dimension. Contrast with Change Parameters which edits values globally without hunting in the timeline. Tell them: if a feature shows a red error marker, double-click it to see what reference broke (usually a deleted edge or face).
Real Tube Stock Sizes
- 2x1 0.1in wall: drivetrain rails, arms.
- 1x1 0.1in wall: light superstructure.
- 2x2: heavy towers, climbers.
- Keep wall = 0.1in to match VersaFrame.
- Hole patterns come in a later lesson.
Ground it in real parts. WCP, AndyMark, and VEX/VersaFrame all sell these. The 0.1in (and sometimes 1/16in / 0.0625in) wall is standard. Tell them that matching real stock means the CAD weighs and fits like the real robot. Foreshadow hole patterns and the 1/2in hex bore stuff coming up.
Your Task
- Set up tubeWidth=2, tubeHeight=1, wall=0.1.
- Model a parametric 2x1 tube.
- Make 3 lengths: 14in, 18in, 24in.
- Use components so all 3 coexist.
- Capture an isometric of all 3 tubes.
- Fusion: File > Share > Public Link.
- Copy the public link.
- Paste it on AltHub for review.
Give them ~20 minutes. Circulate and check that lengths are driven by parameters, not hardcoded. Ask one student to change a parameter live to prove it's parametric. If someone has solid bars instead of hollow tubes, they missed the offset/ring. Public Link sharing is under File > Share in the data panel.
🧰 Add-ins for this step
Use the installed AltSkripts / FRC-COTS tools here — don't do it the slow way.
- FRC Tube Extruder — set a new length per tube; the dialog remembers your last settings.
You Can Now Spin Up Tubes In Seconds
- User Parameters drive sketch + extrude.
- Change the number, the model follows.
- Timeline lets you re-edit any feature.
- Components keep many tube lengths separate.
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.