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Module 3 — Detailed Design for Fabrication

Objective: finalize mechanism geometry and hardware so parts can be made.

Prereqs: Prototype results and selected geometry.

Steps

  • Lock dimensions, center distances, bearing/bushing choices, and hardware.
  • Specify materials and thickness; add tolerances for critical fits.
  • Prepare fab-ready drawings, DXF/STEP, and BOM with fasteners.
  • Define belt/chain tensioning method; add access holes/slots.
  • Add standoffs/gussets for stiffness; check for wrench access on fasteners.

Deliverables

  • Fabrication packet (drawings, DXF/STEP, BOM, notes on tolerances/finishes).
  • Assembly notes for shimming, tensioning, and order of operations.

Instructions (numbered)

  1. Finalize geometry: centers, thicknesses, bearings/bushings, hardware sizes.
  2. Choose materials and set tolerances for critical fits; call out datums.
  3. Define tensioning (slots/turnbuckles) and add access holes.
  4. Add stiffness features (gussets/standoffs) and check fastener tool access.
  5. Create drawings + DXF/STEP; compile BOM with fasteners; include assembly notes.

Example

  • Elevator stage: 2x1 tube 0.090", 0.0015" slip fit bearing blocks, #25 chain 3% tension via slot, 10-32 hardware with nylocks; access slot on back for wrench.

Best practices

  • Dimension to functional datums; avoid chain of dimensions.
  • Specify hardware and threadlocker use on drawing notes.
  • Ensure wrench/driver access in CAD before release.

Common mistakes

  • No tensioning provision; no tool access; missing tolerances.
  • Wrong material thickness; over-constraining with mates.

Checklist

  • Centers/thickness/bearings locked
  • Tolerances and datums noted
  • Tensioning method included
  • Stiffness and access verified
  • Drawings + DXF/STEP + BOM done
  • Assembly notes included

Recommended tools

  • CAD with interference/clearance checks, drawing templates, tolerance table, BOM template.

Sample log (template)

  • Date:
  • Changes made:
  • Tolerance decisions:
  • Access checks:
  • Release status:

Photos/diagrams

  • [Placeholder: annotated CAD view showing tension slots and access]

Resources

  • KOP parts: firstinspires.org/robotics/frc/kit-of-parts