Yonder Robotics · 2026

Robot Gripper

A servo-actuated parallel gripper with integrated infinite rotation. Two DF Robot 45 kg·cm servos feed a gear reduction driving dual four-bar linkages. Fingers stay parallel through full closure at 181 N, a 3.5 factor of safety on the 5 kg requirement.

Grip force

181 N (FoS 3.5 at 5 kg)

Actuation

2 × DF Robot 45 kg·cm servo

Mechanism

Dual parallel four-bar linkage

Rotation

Continuous, through-bore slip ring

Fingers

1/4" 5052 aluminum, water-jet

Slip ring housing

2.5" Ø 6061 tube, 1/16" wall

Structure

Glass-fiber reinforced ABS

Envelope

Under 0.3 m length

Role

Design & manufacture

OnshapeWater jetManual millBambu P1SABS-GF

Design report (PDF)

Sizing the linkage

The grip number came first, on paper. The four-bar was laid out by hand with the servo lever arms marked on it, and grip force falls straight out of the ratio between them. Servo selection, the gear reduction, and the finger stock were all then chosen to hold that number through full closure rather than only at the tip.

Hand concept 1.0: parallel gripper layout and the grip-force derivation

Hand 2.0: fingers, four-bar parallel gripper, metal tube, internal slip ring, hypoid bevel interface

Modularity as the driver

The gripper is independently replaceable. It comes off without redesigning the hand stem, so a future team integrates a new end effector against the same wrist and slip ring interface. Fingers are interchangeable too.

Rotation, structure, and gripping used to be entangled. Separating them is what makes the hand serviceable across seasons.

Hand 2.0: side section through the stem and slip ring

Onshape tree: wrist interface and slip ring, finger and servo interface, plates, bearings

Packaging against the wrist

Wrist torque and size capped the hand at 0.3 m. A through-bore slip ring lets a keyed shaft pass straight through the stem: continuous rotation with no added length, and minimal bending moment fed back into the wrist.

CAD: hypoid interface at the base of the stem

Hypoid bevel gear with the slip-ring wiring through the bore

Assembly

M4 and M5 fasteners throughout, with the slip ring housing captured by top and bottom aluminum caps carrying radial mounting screws: structural retention and service access from the same feature.

Every gripper joint pivots on an M5 shoulder bolt with a precision spacer, which is what keeps the four-bars aligned and the motion repeatable after the hundredth open-close.

Hybrid metal / plastic load path

Fingers water-jetted from 1/4" 5052 aluminum, sandblasted and brushed to a low-friction finish at the bearing interfaces. Servo drive gears use stamped fine-pitch teeth.

The 6061 slip ring housing was machined by hand with a custom radial marking jig for hole placement. Structure and enclosures print in glass-fiber ABS on a Bambu P1S with a hardened nozzle. Joints pivot on M5 shoulder bolts with precision spacers.

Structural load stays in metal, mounting geometry stays in plastic. Rigidity without giving up iteration speed.