Part Design for Robotics — RoboCAD Academy

Interactive 3D Model: Wheel & Axle — a revolved wheel with spokes and central hub on an axle shaft.

Designing Durable Robot Parts

A robot is only as strong as its weakest part. Understanding materials, geometry, and tolerances ensures your parts survive real-world forces.

Common Materials in Robotics

Material	Pros	Cons	Common Use
Aluminum (6061)	Light, strong, machinable	More expensive than steel	Structural plates, brackets
PLA Plastic	Easy to 3D print, cheap	Brittle, low heat tolerance	Prototypes, sensor mounts
PETG	Tough, flexible, printable	Harder to print than PLA	Functional parts, guards
Polycarbonate	Extremely impact-resistant	Needs enclosure to print	Armor, shields, gears
Steel	Very strong, durable	Heavy, harder to machine	Shafts, axles, gears

Tolerances & Fits

Tolerance is the acceptable range of variation for a dimension. Getting this right means parts actually fit together.

Clearance Fit

The shaft is always smaller than the hole. Parts slide or rotate freely. Used for: pins in pivot joints, axles in bearings.

Transition Fit

The shaft and hole are nearly the same size. Might need light pressing. Used for: locating pins, alignment features.

Interference Fit

The shaft is larger than the hole — requires force to assemble. Used for: press-fit bearings, permanent joints.

Design Features for Strength

Fillets on internal corners: Reduce stress concentrations that cause cracks. Always fillet load-bearing corners.
Ribs and gussets: Thin walls of material that add stiffness without adding much weight.
Lightening patterns: Pocketing or hex patterns remove material from low-stress areas to reduce weight.
Uniform wall thickness: Especially important for 3D-printed and injection-molded parts to prevent warping.

Robotics Tip: For 3D-printed parts, orient your print so that layer lines run parallel to the forces, not perpendicular. A part is weakest between layers.

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