Suspension

The RoboFlock suspension is a passive rocker-differential linkage. It has no springs, dampers, or active components — instead it uses a single geometric constraint to keep all four wheels in ground contact across uneven terrain.

The mechanism is built up in two stages: an independent per-side pivot, and a dependent front cross-link that couples the two sides together. The two stages combine to give a single articulation axis with anti-symmetric travel between left and right.

Stage 1 — Independent Per-Side Pivot

Each side of the robot can rotate independently about a single horizontal axis that runs left-to-right across the centerline of the robot. The side itself — extrusion, both motor brackets, both wheels — is rigidly attached together, so the entire side rocks as a unit.

The pivot axis is built from two nested mechanical interfaces:

Outer interface (frame ear bearings). The 3D-printed main chassis frame has two L-shaped ears that drop down from above the extrusions. Each ear has a ball bearing pressed into its lower face. The inner race of each bearing rides on the outer diameter of a hollow rod stub.
Inner interface (centerline through-shaft). Each side’s hollow rod stub extends inboard from a 12 mm pivot hub (RV1-SUS-HUB-001). The two stubs from left and right meet near the centerline. A solid linear rod is slipped inside both hollow stubs so that one rod bridges across — this acts as a sliding plain bearing between the two halves and locks the pivot axes of the two sides into a single shared line.

Each pivot hub bolts to a printed rocker body bracket (RV1-SUS-RBR-001) via 4× M4 SHCS. The rocker body bracket itself slides onto the 4080 extrusion and clamps with 4 bolts (2 into the top T-slot, 2 into the bottom).

Note

At this stage — independent pivot only, no front cross-link installed — the two sides are mechanically disconnected from each other. If you articulate one side, the other does not move. The dependent behavior is added in Stage 2.

Stage 2 — Dependent Cross-Link (Rocker-Differential Arm)

At the front of the main chassis frame, a 3D-printed differential arm (RV1-SUS-001) sits on a vertical shoulder bolt that threads upward into the frame. The arm pivots in the horizontal plane.

Two pushrod assemblies (RV1-SUS-002) connect this arm to the two side suspensions, one per side. Each pushrod is a length of threaded rod with a ball-joint rod end at each tip:

The upward-facing rod end attaches to the differential arm.
The side-facing rod end (90° rotated) attaches to a mount on the side’s rocker body bracket.

Geometry is mirror-symmetric across the centerline. As one side pivots upward, its pushrod rotates the differential arm in one direction; the opposite-side pushrod, attached to the same arm but on the other side, is forced to translate the matching distance in the opposite sense — pushing the other side down.

The result is anti-symmetric travel: when one side is pushed up by an obstacle, the other side is geometrically driven downward by the same amount, keeping the average pitch of the body constant and keeping all four wheels loaded against the ground.

Note

Pushrod length is set on assembly (via the threaded rod between the two ball-joint ends) and defines the static ride height. After initial assembly, set both pushrods to the same length with the robot on a flat surface so the body sits level; lock the rod ends with jam nuts.

Articulation Limits

The mechanical articulation envelope is bounded by:

The clearance between the rocker body bracket and the frame ears as the side pivots upward (the upper hard stop)
The angle at which the ball joints reach the end of their rotational travel (the geometric stop on either side)
The clearance between the wheels and the underside of the hull (the lower hard stop on the opposite side)

Important

Verify the actual articulation envelope on the assembled prototype before field testing — TBD pending first build measurements.

Caution

Failure Modes to Watch

Ball joint loosening. Vibration over rough terrain backs jam nuts off. Re-torque after every test session.

Frame ear bearing seat creep. Repeated articulation under load can deform the printed bearing seat. Inspect for ovalization periodically and reprint the frame if the press fit becomes loose.

Centerline rod gallng. The inner sliding rod relies on the hollow stub bores being clean. Wipe down and lightly lubricate during reassembly.