Shafts & Bearings
STAGE 1B · POWER — Shafts, bearings, bores, and retention in Fusion 360
Shafts Carry The Power
A shaft is the spinning rod motors drive.
- Gears, pulleys, and wheels mount on shafts.
- Bearings let shafts spin with low friction.
- Get the bore wrong and nothing fits.
- Standardizing sizes saves you in the pits.
Frame the whole power path: motor -> gearbox -> shaft -> wheel/mechanism. Everything in this lesson is the 'middle' of that chain. Tell them FRC runs on a handful of standard sizes — once you learn them, parts just click together. The #1 build-season mistake is mismatched bore sizes.
Hex Vs Round
- Flat-to-flat = 0.500in
- Drives gears & pulleys — no slip
- FRC default for power transmission
- Hex bore parts lock to it instantly
- Common: 0.375in / 0.500in dia
- Spins freely — needs a key or clamp
- Used for dead axles & idlers
- Smoother in plain bearings
Hex is king in FRC because the flats transmit torque with zero slip and zero setscrews — a gear with a hex bore simply cannot spin on the shaft. Round shaft needs a keyway or clamping collar to transmit torque, so we mostly use it for dead axles (a shaft that holds a spinning part but doesn't itself spin). Emphasize: measure hex flat-to-flat, NOT corner-to-corner.
Draw The Hex Profile
New component first — name it "Hex Shaft".
- Sketch on a plane: Polygon > Circumscribed, 6 sides.
- Set the inscribed dimension to 0.500in.
- Extrude to your length (e.g. 6in).
- Make it a body inside its own component.
Demo live: Create > New Component BEFORE sketching — this keeps the shaft as its own assembly item so you can add Joints later. Use the Circumscribed polygon so the 0.500in dimension lands on the flats, not the corners. Common mistake: students dimension corner-to-corner and get a shaft that won't fit any hex bore. Extrude is under Create > Extrude or press E.
Use A Parameter For Bore
Modify > Change Parameters in Fusion.
- Add user parameter: hexFlat = 0.5 in.
- Type "hexFlat" into the polygon dimension.
- Change one number, every shaft updates.
- Match Onshape Variables — same idea here.
This is the Fusion equivalent of Onshape Variables. Parameters live in Modify > Change Parameters. Tell them to name it clearly (hexFlat) and reference it by name in dimensions. The payoff: when REV ships a 0.502in nominal hex or you switch to 3/8 hex, you edit ONE value. Great habit for keeping a whole assembly consistent.
What A Bearing Does
Lets a shaft spin freely in a fixed plate.
- Inner race spins, outer race stays put.
- FRC standard: 1/2in hex-bore flanged bearing.
- Flange seats against the plate face.
- Press-fit into a 1.125in bore hole.
A bearing separates spinning from stationary with low friction. The classic FRC part is the flanged ball bearing with a 1/2in HEX inner bore (so the hex shaft drops straight in, no setscrew needed) and a 1.125in round outer diameter that press-fits into a plate. The flange keeps it from sliding through. Hand around a real bearing if you have one.
Hex-Bore Vs Round-Bore
- Inner race is a 1/2in hex hole
- Transmits torque — locks to hex shaft
- Use on driven/powered shafts
- No key, no setscrew needed
- Inner race is a round hole
- Shaft spins freely inside it
- Use on dead axles & idlers
- Cheaper, more size options
Key distinction students confuse: a HEX-bore bearing makes the shaft and bearing inner race spin together — used where the shaft delivers power. A ROUND-bore bearing lets the shaft spin independently — used on dead axles where the shaft is bolted stationary and only the gear/wheel spins. Picking the wrong one means your mechanism either binds or can't transmit torque.
Drop In Vendor Cad
Don't model bearings — download them.
- Grab STEP/F3D from REV, WCP, AndyMark.
- Insert > Insert Mesh/Derive, or open & paste.
- McMaster-Carr for hardware & shaft collars.
- This is Fusion's version of MKCad.
frcdesign uses Onshape's MKCad library; in Fusion you pull the same parts as STEP or F3D files from vendor sites — REV Robotics, WestCoast Products, AndyMark, ThriftyBot — and McMaster-Carr for hardware (McMaster has a CAD download button on every part page). Insert via Insert > Insert Mesh or File > Open then copy the body in. Tell them: NEVER hand-model a bearing for a real design — use the vendor's exact geometry so holes line up.
BEARINGS HOLD, RETENTION KEEPS.
A bearing locates the shaft sideways — but something else must stop it sliding out lengthwise.
Stop The Shaft Walking
- Snaps into a machined groove
- Cheap, light, low-profile
- Needs a groove cut in shaft
- Use 'clipping shaft' from vendors
- Clamps onto shaft, no groove
- Adjustable position, reusable
- Clamping > setscrew style
- Bulkier but rock-solid
Two common retention choices. E-clips (and shaft retaining rings) drop into a pre-cut groove — vendors sell hex shaft with grooves already machined, or you spec them. Shaft collars clamp around the shaft anywhere — go clamping-style, not single-setscrew, because setscrews mar the shaft and loosen under vibration. Rule of thumb: a clip or collar on BOTH sides of a bearing pins the shaft axially. Pull collars from McMaster CAD.
Joints, Not Mates
Onshape Mates = Fusion Joints.
- Rigid joint: bearing-to-plate, collar-to-shaft.
- Revolute joint: shaft spins in the plate.
- Assemble > Joint, pick two faces/edges.
- Lets you motion-test the mechanism.
Translate the vocab explicitly: what Onshape calls Mates, Fusion calls Joints (Assemble > Joint, or press J). Use a Rigid joint to lock parts that don't move relative to each other (bearing into plate, collar onto shaft). Use a Revolute joint for the spinning shaft so you can drag it and verify clearance. Ground the main plate first (right-click > Ground) or the whole assembly will fly around.
When There'S No Plate
A bearing block holds a bearing off-plate.
- Bolts to tube or frame, carries the bore.
- Common on swerve & arm pivots.
- Buy them: REV, WCP MAXSwerve, ThriftyBot.
- Or model a block with a 1.125in bore.
Sometimes you can't press a bearing directly into a structural plate — the bearing needs to sit out in space or on a tube. A bearing block is a chunk of aluminum with the 1.125in bore that bolts to your frame. You'll see them all over swerve modules and arm pivots. Mostly you buy these, but if you model one, reuse your bore parameter so the hole matches your bearing OD exactly.
Your Task
- Model a 6in 1/2in hex shaft (parameter)
- Insert a vendor hex-bore flanged bearing
- Mount bearing in a plate w/ 1.125in bore
- Add a shaft collar each side, Joint it all
- Revolute-joint the shaft, drag to test
- Confirm no interference (Inspect > Interfere)
- Fusion Share > Public Link
- Paste the link on AltHub
Walk the room while they build. Checkpoints: (1) hex dimensioned flat-to-flat off the parameter, (2) bearing is a downloaded vendor part not hand-modeled, (3) bore is 1.125in, (4) collars on both sides, (5) a working Revolute joint they can drag. Run Inspect > Interference to catch a too-tight bore. Submit via Fusion Share public link pasted on AltHub — remind them to set it Public or mentors can't open it.
🧰 Add-ins for this step
Use the installed AltSkripts / FRC-COTS tools here — don't do it the slow way.
- Shaft Endings — add e-clip grooves and center holes to 1/2", 3/8", 1/4" shafts.
Shafts Move Power, Bearings & Retention Keep It
- Hex for torque, round for dead axles.
- Bearings locate radially — clips/collars hold axially.
- Insert real vendor CAD; assemble with Joints.
Your Task
- Model what this lesson covers in Fusion 360.
- Use the AltSkripts tools where they apply.
- Save it with a clear name.
- In Fusion: Share → Public Link → Copy.
- Paste the link below.
- A coach reviews it in AltHub.