Drivetrain Frame
Stage 1A · Part Modeling — Sketch the perimeter, plan the tubes, model the rails
The Frame Is The Foundation
Every subsystem bolts to the drivetrain frame.
- Get sizing wrong and the whole robot is wrong.
- Frame defines your wheelbase and track width.
- We model it first, everything else hangs off it.
Set the stakes. The drivetrain frame is literally what the rest of the robot mounts to — intake, elevator, bumpers, electronics board. If the frame perimeter is wrong, bumpers won't fit and you fail inspection. Tell them we build bottom-up: frame first, then modules, then superstructure. This mirrors how a real FRC season starts.
Frame Perimeter & Sizing
Frame perimeter is the bumper-mounting outline.
- Common kitbot footprint: 26in x 26in or 28in x 28in.
- Max frame perimeter per game rules (often ~120in).
- Plan for 1in to 5in tall bumpers around it.
- Leave room: modules eat the corners.
Explain frame perimeter = the convex outline the bumpers wrap. Real FRC rule of thumb: pick 26-28in square for a swerve bot. Mention the game manual sets a max perimeter (~120in) and max footprint. Common mistake: students dimension to the outside of bumpers, not the frame rail. We dimension the rail outline; bumpers add outward.
Start A New Component
Right-click top of browser > New Component.
- Name it 'Drivetrain Frame' so the tree is clean.
- Activate it (dot next to name) before sketching.
- Save the design with a real name early.
In Fusion we work inside Components, not loose bodies. Demo: right-click the top node, New Component, rename. Stress the activation dot — if it's not active, your sketch lands in the wrong place and joints get messy later. This is the #1 beginner trip: modeling everything in the root. One component = one frame for now.
Sketch The Perimeter
Create Sketch on the XY (top) plane.
- Draw a center rectangle from the origin.
- Dimension it 28in x 28in (D shortcut).
- Confirm the sketch is fully constrained (black).
- Finish Sketch.
Use the Center Rectangle tool so the frame is symmetric about the origin — this makes mirroring modules trivial later. Press D for dimension. Black lines = fully defined; blue = under-defined. Make them check the color. Working in inches: set document units to inch under Document Settings if it defaults to mm.
Plan The Tube Placement
FRC frames are built from 2x1 aluminum tube.
- Tube cross-section: 2in tall x 1in wide, 1/16in wall.
- Rails sit INSIDE the perimeter line.
- Decide overlap: rails butt or miter at corners.
- Sketch the 1in-wide tube paths on the rails.
2x1 (two-by-one) extruded aluminum is the FRC standard for drivetrain rails. The 1in dimension is the width you see from the top; the 2in is the height. Discuss corner strategy: butt joints (one rail runs full length, the other dies into it) are simplest to fabricate. Use Offset (O) to pull the perimeter inward 1in to get the inner tube edge.
MODEL THE WALL, NOT THE WHOLE BLOCK.
2x1 tube is hollow — a 1/16in wall. Extrude the tube profile, not a solid square, so weight and reality match.
Sketch The Tube Wall
Sketch on the end face plane of one rail.
- Draw a 2in x 1in outer rectangle.
- Offset inward 1/16in for the wall thickness.
- This ring is the tube cross-section.
- Finish Sketch.
Show the offset trick: draw the outer 2x1, select all four lines, Offset (O), type 0.0625, pull inward. That gives the hollow ring. 1/16in = 0.0625in is the standard wall. Optionally chamfer or round inner corners later, but skip for now. Make sure the ring is a closed region — Fusion shades closed profiles.
Extrude The Rails
Press E to Extrude the ring profile.
- Set distance to the rail length (e.g. 28in).
- Operation: New Body for the first rail.
- Repeat for all four rails of the frame.
- Use Rectangular Pattern or mirror to speed it up.
E = Extrude. Select the hollow ring, pull to length. First rail = New Body; if you'd extruded a solid you'd get a bar, not a tube — point at the hollow center to prove it's real tubing. For the four rails, you can sketch each path or use Mirror about the origin planes (symmetry pays off here). Watch the operation dropdown — Join vs New Body matters.
Drive It With Parameters
Modify > Change Parameters to add User Parameters.
- Create 'frameWidth' = 28in, 'frameLength' = 28in.
- Add 'tubeWall' = 0.0625in.
- Type the parameter name into dimension fields.
- Change one number, whole frame updates.
This is Fusion's version of Onshape Variables. Modify > Change Parameters > add User Parameter. Then in any dimension box, type 'frameWidth' instead of 28. Now resizing the whole drivetrain is one edit. Huge for FRC where the team debates 26 vs 28in for weeks. Common mistake: forgetting units — type 28 in and Fusion keeps it parametric.
Your Task
- New component 'Drivetrain Frame'.
- 28in x 28in center-rectangle perimeter.
- Four 2x1 tube rails, hollow 1/16in wall.
- Driven by frameWidth & frameLength params.
- Verify rails are hollow (orbit & check).
- File > Share > Public Link.
- Copy the generated link.
- Paste it on AltHub under this lesson.
Give them 25-30 minutes. Walk the room. Check three things: component is activated (not modeled in root), tubes are hollow not solid, and dimensions reference parameters not raw numbers. For submission, Fusion's Share > Public Link generates a viewable link with no account needed — that's our Onshape-share equivalent. Paste on AltHub.
🧰 Add-ins for this step
Use the installed AltSkripts / FRC-COTS tools here — don't do it the slow way.
- FRC Tube Extruder / Tubify — build each frame rail as a real walled tube.
Frame Done Next: Swerve Modules
- Component-first, hollow-tube modeling is the FRC habit.
- Parameters make resizing the robot a one-click change.
- Next lesson: mount MAXSwerve modules to these corners.
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.