12 · ME 240
Full product development cycle for a bicycle brake caliper — needs analysis, Castigliano's method hand calculations, topology optimization, FEA, SLS 3D printing in Nylon 12, and ISO 4210 compliance testing across two design iterations.
Objective
This project ran the complete engineering design process end-to-end — defining quantitative performance targets from ISO standards and benchmarking, generating concepts through Castigliano's method hand calculations, running topology optimization and FEA in Siemens NX, fabricating in Nylon 12 via SLS, and physically testing under real conditions. The project spanned two complete design-build-test-iterate cycles.
The headline story: Iteration 1 passed five of six quantitative targets but failed at the one that actually mattered — it could not stop a bicycle. It had been over-optimized for mass at the direct expense of stiffness. Iteration 2 reversed those priorities entirely. It worked.
Design Targets
The ideal stopping distance (13.38 m) was derived directly from the ISO 4210-2 formula using m = 100 kg, v = 25 kph, μ = 0.6, and the caliper's own component geometry. Bottom-out force was derived from a Castigliano's method cable-pull displacement analysis — a hand-calculation cross-check performed before any FEA was run.
| Metric | Ideal | Marginal |
|---|---|---|
| Cost | $15.00 | $24.00 |
| Stopping distance at 25 kph | 13.38 m | 15 m |
| Weight | 300 g | 400 g |
| Volume of printed filament | 297 cm³ | 396 cm³ |
| Number of individual parts | 5 | 15 |
| Bottom-out force | 100 N | 95 N |
Load Path Analysis
Design-space FEA applied a 100 N tension load at the brake cable holes, a pivot constraint at the pivot holes, and combined normal and shear loads at the brake pad contact locations. Topology optimization in NX identified the two primary load paths: pivot hole → cable attachment, and pivot hole → brake pad contact point.
Stress singularities appeared around the pivot holes in both FEA and topology optimization results. These were correctly identified as numerical artifacts of the idealized pivot constraint, not genuine failure predictions.
Iteration 1 — Mass-Minimized
Simple L-bracket geometry, deliberately thinned arms, prioritizing minimum mass and filament volume above all else.
| Metric | Ideal | Marginal | Iteration 1 | Status |
|---|---|---|---|---|
| Cost | $15.00 | $24.00 | $8.20 | PASS |
| Stopping distance | 13.38 m | 15 m | 46.48 m | FAIL |
| Weight | 300 g | 400 g | 27.2 g | PASS |
| Volume | 297 cm³ | 396 cm³ | 26.71 cm³ | PASS |
| Aesthetic satisfaction | 80% | 50% | 85% | PASS |
| Bottom-out force | 100 N | 95 N | 80 N | FAIL |
The arms were simply too thin to generate sufficient braking force — stopping distance came in at more than triple the marginal limit.
Iteration 2 — Full Redesign
Material was deliberately concentrated at the brake pad contact points and pivot holes; arm cross-sections were substantially thickened; a truss-like structure was introduced for the left caliper, with the right caliper made more robust throughout.
| Metric | Ideal | Marginal | Iter. 1 | Iter. 2 | Status |
|---|---|---|---|---|---|
| Cost | $15.00 | $24.00 | $8.20 | $21.40 | PASS |
| Stopping distance | 13.38 m | 15 m | 46.48 m | 13.3 m | MEETS IDEAL |
| Weight | 300 g | 400 g | 27.2 g | 139.7 g | PASS |
| Volume | 297 cm³ | 396 cm³ | 26.71 cm³ | 138.3 cm³ | PASS |
| Aesthetic satisfaction | 80% | 50% | 85% | 80% | PASS |
| Bottom-out force | 100 N | 95 N | 80 N | 150 N | EXCEEDS IDEAL |
Final Physical Testing
The Iteration 2 calipers were printed in Nylon 12 via SLS and mounted to an actual bicycle for ISO 4210 compliance testing. In testing, they successfully stopped a bicycle cruising at 25 kph in 13.3 m — meeting the ideal stopping distance target — while producing a bottom-out force of 150 N, 50% above the 100 N ideal. The test directly confirmed that stiffness, not mass minimization, is the governing design requirement for a functional brake caliper.
Reflection
Five of six quantitative targets passing does not mean a design works. The one metric that defines the part's actual function — stopping distance — has to govern, even at the cost of every other metric.
Stress singularities around the pivot holes in both FEA and topology optimization were correctly identified as numerical artifacts of the idealized constraint, not genuine failure predictions — a good example of engineering judgment layered on top of software output.
The final design's high factor of safety indicates material overuse. Future work would use topology optimization not to arbitrarily cut weight, but to redistribute material more precisely — concentrating it near the pivot/pad contacts and removing it from low-stress side regions, with the specific goal of bringing cost back under the $24 marginal target.