DIY bimanual SCARA robot arms for fabric manipulation. Simulation-first design approach -- validate in sim before detailed CAD or hardware.
| Joint | Actuator | Ratio | Output Torque | Controller |
|---|---|---|---|---|
| Shoulder (J1) | Kraft QDD (modified) | 5:1 cycloidal | ~10 Nm | moteus r4.11 |
| Elbow (J2) | Kraft QDD (modified) | 5:1 cycloidal | ~10 Nm | moteus r4.11 |
| Wrist Pitch (J3) | T-Motor GB4008 | Direct drive | ~0.7 Nm | moteus r4.11 |
| Wrist Roll (J4) | T-Motor GB4008 | Direct drive | ~0.7 Nm | moteus r4.11 |
| Z-axis | NEMA17 + brake | GT2 belt | — | Stepper driver |
Cost: ~$433/arm, ~$866 bimanual
Phase S1: Parametric URDF (from specs, no CAD needed)
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Phase S2: PyBullet kinematics & torque validation
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Phase S3: MuJoCo dynamics & cloth manipulation
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Phase S4: Sim-to-real parameter study
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SIM GATE — concept validated
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Phase A: Detailed CAD (build123d parametric)
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Phase B-E: CAD-derived URDF → full validation → hardware
Why this order? Simulation finds kinematic/dynamic problems in hours, not weeks. If the 5:1 ratio doesn't provide enough margin, discover it before winding motors. Cloth fling dynamics need tuning -- do it in sim, not on hardware.
Once simulation validates the concept, detailed CAD follows a strict gate process:
- Design individual parts (build123d, parametric)
- Assemble in CAD (STEP)
- Verify: interference checks, section views, bolt access
- Export: one STL per part, origin aligned to link frame
- Automated validation scripts (32 checks)
- Build URDF from verified CAD
- Final simulation with real geometry
| Layer | Technologies |
|---|---|
| CAD | Python, build123d (parametric) |
| Simulation | PyBullet, MuJoCo |
| URDF | Auto-generated from CAD with inertia calculations |
| Motors | moteus r4.11 (CAN bus), AS5047P encoders |
| Validation | 32 automated scripts (mesh, inertia, actuator sizing, E-stop) |
- Arms: Dual SCARA, ~350mm upper + 350mm forearm + wrist
- Payload: 2-4 kg per arm with fabric gripper
- Z-axis: 300mm vertical lift with counterweight
- Transmission: Backdrivable for safe human-robot interaction
Active development. Simulation-first phases (S1-S4) in progress.
bimanual_robot_build_plan.md-- Master build plan and phase indexdocs/build-plan/-- Detailed phase documents (A1-A6, B-E)docs/actuator-alternatives.md-- Architecture comparison and selection rationale