Phase 3 — Design & CAD¶

Window: Week 2 through Week 3. Subsystems move past this phase independantly. Don't wait for all to be done before moving foward.

Gate: CAD Lock (per subsystem).

Precondition: Prototype Down-Select passed for that subsystem.

Design converts winning prototypes into a manufacturable, integrated robot. The rules here exist because teams cannot afford re-machining a plate three times.

Tooling¶

Primary CAD: Onshape
PDM / versioning: Onshape versions + named releases per part.
File naming: <subsystem>-<part>-<rev> e.g. intake-side-plate-A.

Master Model / Top-Down Assembly¶

A single skeleton part defines the robot envelope. Every subsystem references the skeleton for its interface dimensions.

Skeleton contains:

Frame perimeter (bumper zone limit).
Drivetrain wheelbase and wheel positions.
Battery + roboRIO + PDH mounting anchor points.
Elevator or scoring-mechanism envelope.
Height / extension limits per game rules.

Change the skeleton, every subsystem updates. Only the Robot Lead (student) + Mechanical Mentor edits the skeleton, and edits require gate-review sign-off after CAD lock.

More info in FRC Design

How it works in Onshape

The skeleton holds no machinable geometry — just reference planes, sketches, points, and envelope boxes tied to game rules and shared interfaces.

Skeleton lives in one document, e.g. 2026-Skeleton.
Each subsystem lives in its own document (2026-Intake, 2026-Elevator, etc.).
Subsystem docs pull skeleton geometry in as read-only reference via Derived Part or a linked sketch.
When the skeleton is updated and released, each subsystem pulls the new version and verifies nothing broke.

What a student's first CAD day looks like

CAD Lead sits with the new student and opens the skeleton document. Walks through each sketch and why it exists — usually tied to a game rule or shared interface.
Lead creates the student's subsystem document and inserts the skeleton as reference.
Lead shows the student their subsystem constraints: "your intake bolts here (points), lives inside this box (envelope), cannot extend past this plane (height limit)."
Student designs their parts referencing those. Never re-draws the frame perimeter — always references it.

Weekly rhythm after onboarding:

Student works only in their subsystem doc.
If the skeleton needs to change (e.g. elevator needs 2" more width), student does not edit it — raises it to Robot Lead + Mechanical Mentor.
They evaluate impact on other subsystems, edit the skeleton, release a new version. All subsystems pull the update.

Common student confusion

"Can I just draw the bumper in my file?" No. Reference it from the skeleton so it stays in sync.
"The skeleton is wrong for my subsystem." Don't edit it. Raise the change to Robot Lead + Mechanical Mentor.
"My part won't fit." Good — that's the skeleton catching a conflict early. Redesign your part, or escalate the skeleton change.

Part Numbering¶

Every part gets a number when released. Format:

<team>-<year>-<subsystem>-<seq>-<rev>
e.g., 9999-2026-IN-0004-A     (intake, part 4, revision A)

Subsystem codes: DT drivetrain, IN intake, SC scorer, EL elevator, CL climber, EE electrical.

Rev letter increments on any dimensional change after first release. A rev bump kills the previous rev's fabrication tickets.

Part Release Process¶

A part is not "released" (i.e., cannot be ordered or machined) until:

Part fits in the master-model context — no interference in assembly.
Drawing exists if the part is machined (tolerances, material, quantity, finish).
Reviewed by a second CAD person (student or mentor) — the CAD lead does not self-approve.
Part number assigned per convention above.
Entered in the BOM with vendor, stock link or drawing file, quantity, and lead time.

Part release checklist template: doc-templates/part_release.md.

Subsystem CAD Lock Gate¶

Each subsystem hits CAD Lock when:

All parts released.
BOM complete, orders placed for long-lead items.
Master-model interfaces verified — no floating unconnected components.
Weight budget checked. Center-of-gravity checked.
Motor selection, gear ratio, and travel calculations documented.
Reviewed at CAD Lock gate meeting (see 07_gate_reviews.md).

After CAD Lock, all changes go through Engineering Change Request (doc-templates/ecr.md). No ad-hoc "just tweak that plate."

Typical Freeze Cadence (6-week season)¶

Subsystem	CAD Lock target
Drivetrain	end of Week 2
Primary scoring mechanism	end of Week 3
Secondary mechanism / endgame	mid-Week 4
Electrical panel	mid-Week 4

Drivetrain freezes first because everything mounts to it.

Deliverables (CAD Lock Gate)¶

Complete subsystem assembly in master model.
Every part numbered and drawing-released if machined.
BOM with vendor, cost, quantity, lead time — practice-bot + comp-bot + spares.
Weight + COG analysis.
Motor / gear-ratio calculation notes.
Second-reviewer sign-off.

Handoff to Stage 4 (Manufacturing)¶

CAD Lock triggers: - BOM handed to purchasing student for order. - Drawings handed to fabrication student for machining queue. - Part numbers appear on the manufacturing kanban.

Common Failure Modes

No master model. Two subsystems independently claim the same volume; discovered at assembly.
CAD lead self-approves. Small errors ship. Always second-reviewer.
No part numbers. "Which side plate?" becomes an hourly question by Week 4.
BOM in someone's head. Long-lead item forgotten, arrives after event 1.
Weight discovered late. Robot over 125 lb the day before bag/ship. Track it every gate.
"Just a small change." Every unlogged change is a landmine at integration. Force ECR.

Roles

CAD Lead (student, senior): owns master model, approves releases, runs CAD gate.
Subsystem CAD Owner (student): designs their subsystem, produces drawings.
Second Reviewer (student or mentor): required signoff, not the same as the CAD Lead for that part.
Mechanical Mentor: blocks bad ideas, teaches tolerances, watches weight budget.