Mechanical Design
Joint Layout
The arm follows a 6-DOF anthropomorphic configuration: three shoulder joints that share a common centre, one elbow joint, and two wrist joints.
Base
│
● Joint 1 — shoulder pan (Z-axis rotation)
│
● Joint 2 — shoulder lift (Y-axis rotation)
│
● Joint 3 — shoulder roll (X-axis rotation)
│
────── upper arm (L1 = 250 mm) ──────
│
● Joint 4 — elbow flex (Y-axis rotation)
│
────── forearm (L2 = 230 mm) ──────
│
● Joint 5 — wrist pitch (Y-axis rotation)
│
● Joint 6 — wrist roll (X-axis rotation)
│
[End-effector]DH Parameters
Using the modified Denavit-Hartenberg (MDH) convention:
| Joint | α (prev) | a (prev, mm) | d (mm) | θ |
|---|---|---|---|---|
| 1 | 0° | 0 | 120 | θ₁ |
| 2 | 90° | 0 | 0 | θ₂ |
| 3 | −90° | 0 | 0 | θ₃ |
| 4 | 90° | 250 | 0 | θ₄ |
| 5 | −90° | 230 | 0 | θ₅ |
| 6 | 90° | 0 | 60 | θ₆ |
Joint Limits
| Joint | Min (deg) | Max (deg) | Motor ID |
|---|---|---|---|
| 1 | −180 | +180 | 0x01 |
| 2 | −90 | +90 | 0x02 |
| 3 | −90 | +90 | 0x03 |
| 4 | −135 | +10 | 0x04 |
| 5 | −90 | +90 | 0x05 |
| 6 | −180 | +180 | 0x06 |
Joint 4 (elbow) has a hard mechanical stop at +10° to prevent the forearm colliding with the upper arm. Always enforce this limit in software before sending commands.
Material & Fabrication
- Links: 6061 aluminium extrusion / 3D-printed PLA for prototyping
- Motor mounts: SLA-printed nylon or machined aluminium
- Output shaft: direct coupling to Robstride 00 keyed shaft via 3D-printed adaptor
End-Effector
For initial testing: a passive 2-finger parallel gripper driven by a hobby servo (not on CAN). For manipulation experiments, the gripper can be swapped for a force/torque sensor + compliant fingers.
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