Part

Servo joint

You might say: actuated hinge, servo axis, motorized joint, hobby servo, smart servo, bus servo

A servo joint combines an actuator with a horn or hub, link bracket, supported pivot and fasteners so a commanded axis can hold a known angle. The servo output transmits torque; a bearing or through-axle should carry the link's radial and overturning loads when the design needs that support.

What it does

It converts an actuator choice into a repeatable, serviceable joint while exposing the interfaces that usually cause wobble, binding, overload or wrong zero.

Ask

Is this axis best served by a simple hobby servo and pulse command, or by a smart serial/bus servo with address, feedback and limits; are the horn, bracket, bearing, voltage and controller compatible?

Typical

Conventional hobby servo: start from the maker's pulse interface and calibrated neutral/limits; select torque at the actual supply voltage and leave room for the link and downstream mass. Smart serial/bus servo: match bus type, voltage, unique IDs, controller/interface and the documented position, load, voltage and temperature feedback; configure the chosen limits before motion. Neither label makes a joint safe by itself. With power removed, fit the servo in a bracket, support the opposite pivot with a compatible bearing or through-axle when needed, centre the actuator at its documented neutral, install the matching horn/hub and attach the link without side-loading the output. Check full unpowered travel, screw clearance, horn orientation, cable strain relief and pinch points. On first power, command a tiny range on a restrained, guarded joint; compare measured angle and current with the budget before adding a link. Treat quoted stall torque as a momentary specification, not a continuous holding promise.

Trouble

The horn slips or is the wrong spline, the bearing is missing or clamped incorrectly, the bracket twists, the joint has backlash or binds, a hobby servo buzzes at its endpoint, a bus servo has duplicate IDs or wrong voltage, the output heats while holding, or power removal lets the link fall/backdrive.

Catalogue: Servo interface

• Pulse-command hobby servo: A conventional hobby/PWM servo receives timed pulses; the REV SRS V2 is an example of a configurable pulse servo, not an addressed bus device. Its neutral and pulse-to-angle mapping are component-specific, so calibrate neutral and limits before relying on a joint angle.
• Addressed serial bus servo: An addressed serial/bus servo uses a compatible interface and per-motor identity; read the chosen actuator's documented feedback and operating limits before motion.

Connections

• See also: Links and joints
• See also: Actuators
• See also: Electric motor
• See also: Gearbox
• See also: Motor driver
• See also: Emergency stop
• See also: Safety

Sources

1. Jan, Pololu Servo Control Interface in Detail, Pulse width and calibrationThe pulse width is generally the most important part of the interface, and that is what we intentionally vary to change the command to the servo.
2. Jan, Pololu Servo Control Interface in Detail, Pulse width and calibrationThere is no standard correspondence between the pulse width and the servo position.
3. REV Robotics, Smart Robot Servo V2 documentation, Smart Robot Servo V2 overviewOne SRS V2 can be used as a standard angular servo, a custom angular servo, and a continuous rotation servo by simply changing its settings with the SRS Programmer.
4. REV Robotics, Smart Robot Servo V2 documentation, Angular limitsThe SRS V2 can be easily configured with the SRS Programmer to limit right and left motion at two user-defined angles.
5. REV Robotics, Smart Robot Servo V2 documentation, Smart Robot Servo V2 BasicsSplines are like keys, so only matched types will fit together.
6. Interactive Machines, Shutter robot arm assembly, Steps 4–5, bearing mounts and pan plateAttach both Bearing Mounts to the horn and idler of Servo 2 using 2 Servo Washers and 16 M2.5 x 5mm screws
7. ROBOTIS, DYNAMIXEL Selection Guide, CommunicationTo communicate with DYNAMIXELs using a controller, the same communication interface(TTL or RS-485) must be used.
8. Hugging Face LeRobot, SO-100 assembly and motor configuration, Set the motors IDs and baudratesEach motor is identified by a unique id on the bus.
9. ROBOTIS America, DYNAMIXEL XM430-W350-T product documentation, Supported feedbackreal-time data on position, speed, load, voltage, and temperature
10. ROBOTIS America, DYNAMIXEL XM430-W350-T product documentation, Torque and feedback specificationsEstimated rated torque disclosure : This is an estimated value for continuous torque, calculated at 20% of stall torque.

Unverified: Exact bracket thickness, bearing life, fastener preload, horn spline fit, allowable duty cycle and the safe restrained-test force depend on the chosen components; use their manuals and the risk assessment.

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