Power Intro

Open by pointing at last year's robot. Every moving thing on it is a motor plus a way to deliver that motor's power usefully. Ask students: can a motor lift a 15 lb arm directly? No — it spins too fast and has almost no torque at the output shaft. That gap is what this whole unit solves. Set expectations: this is the lesson where CAD meets physics.

Show real motors if you have them. Emphasize free speed (no load) vs stall torque (won't spin). Motors are fast but weak — that's the recurring theme. NEO and Kraken both have a 1/2in shaft-ish output but use a pinion gear. Mention that almost nobody runs a motor bare; it pairs with a gearbox. Don't go deep on motor curves yet — that's a later lesson.

This is the conceptual heart. Use a hand analogy: spinning a bike pedal super fast in the wrong gear — your legs spin but you go nowhere uphill. A motor at 6000 RPM driving a 4in wheel would theoretically do ~70 mph but stall instantly against the robot's weight. The fix is gearing down: give up speed, gain torque. Plant the word 'reduction.'

Walk the math live on the board: count teeth, divide. A small gear driving a big gear = reduction (slow down). Big driving small = overdrive (speed up). Most FRC gearboxes stack two or three reductions to hit big ratios like 100:1 for an arm. Common mistake: students flip the fraction. Anchor it: 'count the teeth on the gear you're driving INTO, over the one doing the driving.'

Gears must be close together and precisely spaced (center distance matters — a later lesson). Chain and belt let you send power across the robot, like from a gearbox to a far wheel. 20 diametral pitch (20DP) is the team standard for gears. #25 chain and 5mm HTD belt are the go-to for drivetrains and arms. Pass real samples around if you have them.

Why hex and not round? A round shaft needs a key or set screw and can slip; a hex bore self-locks to the shaft's flats and transmits torque cleanly. 1/2in hex is everywhere in FRC — wheels, gears, sprockets all come with a 1/2in hex bore option. This is why your CAD will constantly reference 1/2in hex. Bearings come in hex-bore versions too.

Most power transmission comes pre-engineered. You buy a swerve module or a VersaPlanetary and CAD around it. This is where Fusion's Insert > Insert Derive or inserting a downloaded STEP/F3D comes in — you'll learn that this unit. Tell them: respect the vendor's mounting holes and shaft positions; your job is integrating, not reinventing. MAXSwerve and SDS Mk4 are the popular modules.

Map the Fusion tools to the concepts. In Onshape land this is Part Studios and Mates and FeatureScript; in Fusion it's Components plus Bodies, Joints (rigid/revolute/slider), and add-ins like SpurGear. User Parameters (Modify > Change Parameters) let you type a tooth count or ratio once and have the model update. This slide is the toolbox preview — don't demo deeply, just orient.