This repository provides the mechanical CAD/STL files for a 6-DoF isomorphic master arm developed for robot teleoperation and demonstration data collection.
The design focuses on structural robustness, modularity, and intuitive joint-space teleoperation, with particular attention to reducing mechanical loads directly applied to the servo output shafts.
The master arm follows an isomorphic kinematic design: its joint topology corresponds to that of the slave robot, while the link dimensions can be uniformly scaled.
This enables direct joint-space mapping between the master and slave arms without requiring the two robots to have identical physical dimensions.
The mechanical design is built around four principles:
- Isomorphic kinematic structure
- Bearing-supported joint transmission
- Modular and reusable joint components
- Rapid manufacturing and assembly
The link dimensions are parameterized by a uniform scaling factor, allowing the master arm size to be adjusted while preserving its kinematic correspondence with the slave robot. The current master arm is designed isomorphically with UR5e robot arm, and the designation for other slave arms will be done in the future, which is fast and easy with the modularity.
CAD view of master arm
The main structural feature of the master arm is a servo-driven shaft with dual-bearing support.
Instead of allowing the servo output shaft to directly carry the loads generated by downstream links, the transmission shaft is supported by external bearings mounted to the joint structure.
This creates a separate mechanical load path:
Servo → transmission shaft → joint output
while the external bearings and joint housing carry a large portion of the radial and bending loads.
This design:
- reduces direct non-axial loading on the servo output shaft,
- improves joint structural stiffness,
- reduces mechanical stress on the servo transmission,
- and improves durability under repeated manual operation.
CAD view of the bearing-supported joint transmission structure, showing the servo-driven shaft(in the middle) with external bearing(yellow part) and coupling(blue part) supports.
The bearing-supported transmission structure is reused across multiple joints.
For joints with similar interfaces, the same basic transmission module can be retained while only local mounting dimensions are modified. This reduces the number of independently designed components and simplifies adaptation to different arm configurations.
CAD view of the joint 1 and 2, with the reusable bearing-supported transmission structure aside. The same bearing-supported structure can be adapted to different joints
The current STL set is designed around DYNAMIXEL servo modules:
| Joint | Servo |
|---|---|
| Joint 1 | XM540 |
| Joint 2 | XM540 |
| Joint 3 | XC430 |
| Joint 4 | XC330 |
| Joint 5 | XC330 |
| Joint 6 | XC330 |
Larger actuators are placed closer to the base, while smaller XC-series servos are used toward the wrist to reduce distal size and moving mass.
The servos provide both joint-angle sensing and active torque output, allowing the same mechanical platform to support passive teleoperation as well as active functions such as gravity compensation.
The prototype combines:
- 3D-printed custom structural components
- commercial metal shafts and standard mechanical components
- DYNAMIXEL servo modules
- ball bearings and mechanical fasteners
Custom links and servo mounts are suitable for rapid prototyping by 3D printing, while transmission components that require higher stiffness and dimensional consistency use metal parts.
.
├── XM540_Base.STL
├── XM540_OutputShaft.STL
├── XC430_Base.STL
├── XC430_OutputShaft.STL
├── XC330_Base.STL
├── XC330_OutputShaft.STL
├── Joint1_BearingSeat.STL
├── Joint2_BearingSeat.STL
├── Joint3_Link.STL
├── Joint4_Link.STL
├── Joint5_BearingSeat.STL
├── Joint6_BearingSeat.STL
├── XM540_Base_Mount.STL
├── Bearing_Cover_Male.STL
└── Bearing_Cover_Female.STL
The master arm was developed as the operator-side device of an isomorphic dual-arm teleoperation platform for robot demonstration data collection. The complete system uses direct joint-space mapping between the master and slave arms and was further integrated with gravity compensation, slave-side impedance control, and approximate gripper force feedback. This repository contains the mechanical design files of the master arm. The complete teleoperation system and control algorithms are outside the scope of this repository.