Bumpers

Open with a war story: a robot whose bumpers fell off mid-match got disabled. Stress that bumpers are a graded inspection item every event. Beginners think bumpers are an afterthought; pros design them alongside the drivetrain. We model them so they fit perfectly and weigh what we planned.

The exact letters and dimensions shift slightly year to year, so teach the habit of looking it up, not memorizing. Walk through bumper zone height, corner coverage, and the rule that corners must be covered. Common mistake: students design a cool feature that violates the 7 in band.

Demo the cross-section so they see how the layers stack. The noodles compress, so model nominal diameter and let real foam squish. Point out the fabric is just a thin skin — in CAD we usually skip it or model it as a thin shell so the part isn't gigantic.

This is the Onshape Variables equivalent — in Fusion it is Modify > Change Parameters > User Parameters. Demo adding a parameter, then typing the name into a sketch dimension box. Stress: if the game changes the bumper height next year, you edit one parameter instead of re-drawing everything.

Always make a New Component first (right-click > New Component or the checkbox in the dialog) so the bumper is its own assembly piece, not a body inside the drivetrain. Common mistake: students model one giant bumper ring — real bumpers are segments per side so they fit around the frame corners.

Sweep is cleaner than extrude if your backing wraps a corner, but for a straight segment extrude is fine. Remind them noodles compress in real life, so a tiny overlap with field elements in CAD is okay. The two-noodle stack is the standard way to fill the 7 in zone.

Insert > Insert Derive or Insert McMaster/STEP for real bracket parts (REV and WCP sell bumper brackets). Use Assemble > Joint, rigid type, to lock the bracket to the tube — this is the Onshape Mates equivalent. Inspectors physically shake bumpers; if yours wiggle off you fail. Pin-and-clip is fast for pit swaps.

Run through these fast as a checklist. The nominal-vs-actual lumber thing is the #1 dimensional error: a 1x4 is really 0.75 x 3.5 in. Show them how to confirm bracket placement does not block the battery or main breaker. Bumpers must show team number and alliance color clearly.