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Revolute Joint

In one sentence: Allow one part to spin freely around a single shared axis while preventing all other relative motion — the joint for shafts, hinges, and pins.

Overview

Workbench: Assembly
Menu: Assembly → Joints → Revolute
Shortcut: R
DOF removed: 5 | DOF remaining: 1 (rotation about one axis)

A Revolute joint co-aligns two axes and keeps them co-linear while allowing free rotation about that shared axis. All translation and all off-axis rotation are locked.

Intuition

Think of a door hinge. The hinge pin defines an axis; the door can only rotate about that axis — it cannot slide along the pin, cannot tilt sideways, cannot translate across the room. The Revolute joint encodes exactly this relationship.

The two selected cylindrical faces or circular edges define the axes that will be aligned. After solving, the axes are co-linear and the parts can rotate freely relative to each other about that axis.

When to use it

  • Shaft spinning inside a bearing or housing bore.
  • Pin in a pin joint (clevis, hinge).
  • Hinge between two panels or links.
  • Gear shaft constrained by its housing (combine with a Gears coupled joint for the ratio).
  • Any part that rotates about a known axis.

When NOT to use it

  • Don't use Revolute if the shaft also slides axially — use Cylindrical instead, which allows both rotation and axial translation.
  • Don't use Revolute if only a fixed angle is needed — use Angle to lock the angle without prescribing a physical axis connection.

Step-by-step

  1. Press R or choose Assembly → Joints → Revolute.
  2. Click a cylindrical face or circular edge on Part 1 — this defines the axis.
  3. Click a cylindrical face or circular edge on Part 2 — the mating axis.
  4. Optionally set an Offset (axial distance between the two reference planes) and Rotation (initial angle) in the task panel.
  5. Click OK.

The solver aligns the two axes co-linearly and allows only rotation between them.

Parameters

Parameter Type Default Description
Reference 1 Link — Cylindrical face or circular edge on Part 1
Reference 2 Link — Cylindrical face or circular edge on Part 2
Offset Length 0 mm Axial gap between the two reference planes
Rotation Angle 0° Initial rotation angle of Part 2 relative to Part 1

Angular limits

After creation, the joint's Data properties include optional angular limits:

Property Description
EnableLimitAngle Toggle to enable min/max rotation limits
LimitAngleMin Minimum allowed rotation (degrees)
LimitAngleMax Maximum allowed rotation (degrees)

Limits are enforced during simulation but do not prevent manual part movement in the 3-D view.

Python API

Minimal example

import FreeCAD as App

doc = App.ActiveDocument
asm = doc.getObject("Assembly")

joint = asm.Joints.newObject("Assembly::JointObject", "ShaftBearing")
joint.JointType = "Revolute"
joint.Reference1 = (doc.getObject("Housing"), ["Face5"])
joint.Reference2 = (doc.getObject("Shaft"), ["Face2"])
doc.recompute()

Common mistakes and pitfalls

Selecting a flat face instead of a cylindrical face

A flat (planar) face does not define a unique axis — only a normal direction. The solver may produce unexpected results or refuse to solve. Always select a cylindrical face or a circular edge for Revolute joints.

Adding both Revolute and Fixed between the same parts

A Fixed joint already removes all 6 DOF including the rotational one. Adding a Revolute joint on top creates a conflict — 7 constraints on 6 DOF. Delete the Fixed joint before adding Revolute.

Revolute vs Cylindrical for splined/sliding shafts

If the shaft must both spin AND slide axially (e.g. a splined shaft), use Cylindrical. Revolute locks axial translation.

See also