The Assembly

Frame it: up to now they've modeled single bodies. Real robots are dozens of components that must fit and move together. Fusion's assembly tools let you connect parts the way bolts and bearings do in real life — and verify range of motion virtually so we don't waste aluminum. Stress that a CAD assembly is a digital prototype: if it doesn't move in Fusion, it won't move on the field.

Demo live: model a quick plate, show it's just a Body. Right-click > Create Components from Bodies, watch the icon change in the browser. Common mistake: students try to joint two bodies and the Joint command grays out or behaves oddly. Rule of thumb: if it moves on the robot, it's a component. Name them now — 'Component1, Component2' is how you lose an afternoon.

In FRC the ground is almost always your chassis or the structural plate everything bolts to. Ground it before jointing anything. If students don't ground, dragging one part will fling the whole assembly around the screen. The grounded component shows a thumbtack icon. Only ground ONE thing per moving subsystem.

This is the heart of the lesson. Press J, hover and Fusion offers snap points — corners, edge midpoints, and crucially hole/circle CENTERS (great for bolt patterns and bearing bores). Click source point, then target point, parts snap together. Then choose motion type. Tell them: aim for the bearing bore center or the bolt hole, not a random face, so alignment is exact.

Concrete demo: REV or AndyMark wheel on a 1/2in hex shaft. Snap to the bore center so it's coaxial. Choose Revolute, verify the axis arrow runs DOWN the axle, not sideways. Then grab and drag — it should spin freely. If it won't move, either you grounded the wheel by accident or the axis is wrong. This is exactly how you'd model a drivetrain wheel pod.

This replaces Onshape's MKCad library. For fasteners and bearings, INSERT > McMaster-Carr is gold — browse, pick STEP, it drops in. For modules (MAXSwerve, NEO, Kraken X60), download the F3D or STEP from the vendor and upload it to your Fusion project, then Insert into Design. Inserted geometry comes in as its own component, so it's immediately jointable. Warn them: vendor parts can be heavy/detailed — that's fine for fit checks.

Show two tools. (1) Right-click a joint > Edit Joint Limits to cap an arm at its real travel — this stops CAD from showing impossible positions. (2) Motion Study / Drive Joints to animate and scrub through the range. Tie limits to reality: physical hardstops, an elevator's max extension, a turret's wire-management limit. This is how you confirm the mechanism reaches its target without overtravel.

The payoff step. Drive the mechanism end to end, then run INSPECT > Interference to mathematically detect overlaps you'd miss by eye. Red = parts occupying the same space — impossible in metal. Have them specifically check the 120in frame-perimeter rule and bumper clearance for any mechanism that extends. Remind: range of motion changes whenever geometry changes, so re-verify before declaring 'done.'