Practice: Rollers

Frame it: this is the exact subassembly on almost every intake. Tell them rollers are where 'it works in CAD but jams on the field' happens — spacing and grip are everything. We're practicing the reusable pattern, not a one-off.

This is the Onshape-Variables equivalent. Demo creating a User Parameter before drawing anything. Tell them: if spacing is wrong later, you change ONE number, not five sketches. Common mistake — forgetting units, so type 'in' explicitly.

Biggest rookie error: dimensioning across the points instead of the flats. Hex stock is measured flat-to-flat. Show the construction-circle trick: inscribe the hex in a 0.5in circle won't be right — constrain the flats. Right-click body > Create Component from body.

Joints replace Onshape Mates. For a wheel pressed on a hex shaft, Rigid is correct — it doesn't spin relative to the shaft. Demo picking the joint origins (snap to hex bore center). Don't let them use 'Move' to fake placement; it won't hold parametrically.

This is the payoff of Step 1. Type the parameter NAME into the quantity and distance fields, not a raw number. Now change rollerCount to 4 and watch them multiply. Even pitch is automatic — that's the whole point of even spacing for consistent grip.

Use a real WCP/REV HTD pulley file with the right bore. Pulley goes OUTSIDE the bearing block so the belt clears the structure. Mention 5mm HTD is the FRC standard for low-load belt runs like intakes — quiet and no chain slop.

One Revolute joint defines how the whole spinning assembly rotates. Demo dragging the shaft to confirm rollers spin together. Common mistake: adding a Rigid joint to the plate that over-constrains and locks rotation. The shaft-to-ground relationship is revolute, wheel-to-shaft is rigid.

Run Inspect > Interference — it catches wheels clipping plates or bearings. Teach Measure for verifying pitch numerically, not eyeballing. If a gap is off, fix the parameter, don't nudge geometry. This is the acceptance check before you call it done.