Assemblies and Mates

What an assembly is

A Part Studio is where you make parts; an Assembly is where you put them together. You insert parts and subassemblies, then add mates to position them relative to each other and define how they move.

Mate connectors and mates

Onshape uses mate connectors — small coordinate frames (an origin plus X/Y/Z axes) placed on parts. A mate joins two mate connectors and sets the allowed motion. The main mate types:

• Fastened — fully locks two parts together (zero motion). Use for a plate bolted to a tube.
• Revolute — allows rotation about one axis. Use for a wheel on an axle or an arm pivot.
• Slider — allows sliding along one axis. Use for an elevator carriage on rails.
• Cylindrical — rotate and slide on one axis (like a shaft in a bushing).
• Planar, Ball, Pin-slot, Parallel, Tangent — for more specialized connections.

Because mates can model real motion, you can drag your assembly to test the range of motion: does the arm swing where you expect, does the elevator reach full height, does anything collide?

A consistent mating strategy

A reliable approach many FRC teams use:

1. Place a clear reference (some teams add an Origin Cube FeatureScript) to anchor the assembly.
2. Fasten the base subsystem (often the drivetrain) to the assembly origin.
3. Build outward, mating each subsystem to known references rather than to random faces.
4. Use the right mate type so motion reflects reality.

Subassemblies keep big robots manageable

You rarely build the whole robot as one flat list of hundreds of parts. Instead you create subassemblies — a complete gearbox, a complete intake — and insert those into the top-level robot assembly. This mirrors the subsystem structure of the robot and lets multiple designers own different subassemblies in parallel. It also keeps the assembly fast and the BOM organized.

Check interferences

Onshape can detect interferences — places where two parts overlap in space. Run an interference check on your assembly before manufacturing; overlapping parts mean something won't physically fit. Combined with mate-driven motion, this catches a huge fraction of design mistakes before any metal is cut.

Why mates matter for the rules

With a complete, mated assembly you can verify rule compliance: measure the robot perimeter against the R104 limit of 110 in, the height against 30 in, and drive an extension to confirm it stays within the 12 in extension limit (R105) in 2026 REBUILT.

Practice by assembling a simple two-plate gearbox with a shaft (revolute) and bolts (fastened). The Stage 1A and swerve-drive assembly exercises in FRCDesign.org are excellent for this.