Part Design for Robotics - RoboCAD Academy

A wheel on an axle - the hole for the shaft uses a clearance fit, so it spins freely.

1Experience

2Reflect

3Theorize

4Apply

Pick the Right Material

Aluminum 6061: Light, strong, machinable. Use for structural plates and brackets.
PLA: Cheap and easy to print. Great for prototypes and sensor mounts.
PETG: Tougher than PLA and flexes without snapping. Use for functional parts and guards.

Rule of thumb: If it carries load, go aluminum. If it just has to hold shape, print it.

Tolerance is how much a dimension can vary and still work. Parts that meet each other need the right fit.

Clearance fit: Hole is bigger than the shaft. Parts slide freely - use for axles and pivots.
Interference fit: Shaft is bigger than the hole. Takes force to assemble - use for press-fit bearings.

A good starting clearance for a 3D-printed hole around a 6 mm shaft is about 0.3 mm on the diameter.

Fillets on inside corners: Sharp corners crack first. A small fillet spreads the stress.
Ribs: Thin walls flex - add a rib and the stiffness jumps with almost no weight.
Lightening patterns: Hex or triangle cutouts in low-stress areas drop mass.

Pause and Reflect

When would you choose a clearance fit over an interference fit?

Why does adding a small fillet to an inside corner make a part stronger?

✓ Your reflections are saved automatically

Apply What You Learned

Design a sensor mounting bracket that bolts to a 1/4" aluminum chassis plate and holds a small camera.

Pick a material based on loads and whether it needs to flex.
Size the bolt holes with a clearance fit for M3 hardware (3 mm metric bolts — use a 3.2–3.4 mm hole for easy pass-through).
Add fillets on inside corners where stress would concentrate.
Reduce mass with a pattern of lightening holes in low-stress areas.

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