Motor Mounting

Open with a real failure story: a plate fab'd with a 1.5in pilot when the MAXPlanetary needs 1.625in. Motor pinion rubs, gearbox sits crooked. The motor mounting plate is the interface between electrical (the motor) and mechanical (your robot). Two things must be perfect: the bolt circle and the pilot bore. We'll learn both, then import the real motor to prove it fits.

Define terms clearly. Bolt circle diameter (BCD) is the diameter of the circle the hole centers sit on. Pilot bore is the precision center hole that locates the part - it carries the load, the bolts just clamp. Stress that the pilot does the centering, NOT the bolts. Students always think the bolts align it. Pull up the REV MAXPlanetary mounting spec page live so they see real numbers.

Demo navigating to revrobotics.com, finding the MAXPlanetary, opening the Documents/CAD tab. Show that real teams design to published specs, never eyeball. Common mistake: copying a number from an old whiteboard sketch. The vendor drawing is the source of truth. Have students record: pilot dia, bolt circle dia, number of bolts, bolt size (e.g. #10-32 clearance).

This is the Fusion equivalent of Onshape Variables. Open Modify > Change Parameters, click the + under User Parameters. Add pilotDia = 2.0 in, boltCircle = 2.0 in, boltDia = 0.196 in (#10 clearance), boltCount = 4. Explain you can type these names into any dimension box. The payoff: when the team switches motors, you edit parameters, not geometry. This is the single biggest pro habit in this lesson.

Make sure students sketch ON the plate face and snap the circle center to the origin point. Dimension by typing pilotDia in the box - it turns the dimension into a parameter link (shows fx:). Then Create > Extrude, select the circle profile, set operation to Cut, extent All. Common mistake: not centering on origin, so the whole pattern drifts. The pilot is your datum - everything references it.

Sketch one circle, dimension its center to boltCircle/2 from origin (radius, not diameter - this trips people up). Dimension the hole itself to boltDia. Cut it. Then Create > Pattern > Circular Pattern, pick the cut feature, axis = the center construction axis or origin Z. Type boltCount in quantity. Spacing stays full 360. Show that editing boltCount to 6 instantly re-patterns. Mistake: patterning the sketch instead of the cut feature.

Two paths: upload the STEP to the Data Panel then Insert > Derive/Insert into Current Design, or use Insert > Insert McMaster-Carr for hardware. STEP files come in as a single solid body - that's fine for fit-checking. Tell them: vendor STEP is the ground truth for whether their pattern is right. Heads up that big assembly STEPs can be slow - the MAXPlanetary is fine, a full swerve module is heavier.

This is Fusion's version of Onshape Mates. Assemble > Joint, set type to Rigid (motor doesn't move relative to plate). Pick the motor pilot circular edge, then the plate pilot bore edge - they snap concentric. Now visually verify the 4 bolt holes line up with the motor's tapped holes. If they don't, your BCD or hole angle is off. This is the moment the import pays off - it catches mistakes before fabrication. Revolute joint is for shafts that spin; this mount is Rigid.