01 Basics
1.1 Working principle
SR-Support is a 2-DOF (shoulder + elbow) active self-righting device:
- Mechanism: a two-joint arm mounted on a square base; the shoulder swings about the body's long axis and the elbow folds the forearm;
- Sensing: a 6-axis IMU provides the attitude quaternion; the firmware classifies each fall into one of four poses (
pitch_pos/neg,roll_pos/neg, see page 06 6.5) from the body-frame up vector; - Actuation: a reference-sequence executor - each pose has a waypoint schedule (20 ticks per waypoint, 0.08 rad/tick slew) that plants/levers the arm to roll the body back upright;
roll_negadditionally uses elbow-wedge pumps and a whip-slam fallback; - Fallbacks: 14 s timeout, pose re-planning and automatic retry after the fall gate;
roll_neguses per-stage adaptive holds and exits to retract as soon as it is upright; - Verified: four directions stand up directly in about 1-6 s; the same model drives the MuJoCo simulation and the live hardware twin (page 08).
1.2 Overview
| Item | Specification |
|---|---|
| Base | ~88 × 82 mm, 68 mm tall (bottom plate + shoulder servo mount, 3D printed) |
| Arm | Shoulder axis 56 mm above the base, elbow 40.1 mm above the shoulder; forearm strut ~17 cm (12 mm tube) |
| Mass | ~133 g (model mass table: foot 92.1 / arm1 20.7 / arm2 20.1 g, including both servos) |
| Shoulder | PTK7452MG; manual limits [-1.85, +1.82] rad (sim joint range [-1.07, +2.07]) |
| Elbow | PTK7452MG; manual limits [-0.90, +0.70] rad (mechanical ~±1.55 rad) |
| Controller | ESP32-S3-DevKitC-1 (Arduino framework / PlatformIO) |
| Attitude | Juxi ICM42670P 6-axis IMU (I²C address 0x23, 100 kHz) |
| Servo drive | ESP32 LEDC, 50 Hz, 14 bit, 500–2500 µs pulse width |
1.3 BOM
| Category | Part | Qty | Notes |
|---|---|---|---|
| Structure | 3D printed: bottom plate, shoulder servo mount, elbow servo mount, top strut | 1 each | PETG or PLA, 15% infill; servo horns are the ones bundled with the servos |
| Actuation | PTK7452MG 180° PWM servo | 2 | Metal gear, 25T, ~12.2 g, ~3.4 kg·cm at 6 V |
| Controller | ESP32-S3-DevKitC-1 | 1 | USB-C |
| Sensor | Juxi ICM42670P IMU module | 1 | 3.3 V supply |
| Adapter | Passive servo adapter board | 1 | GPIO → 3-pin headers, shared V+/GND, no PCA9685 |
| Wiring | USB-C data cable, Dupont wires, servo extensions | several | — |
| Power | Servo supply 5 V / ≥5 A | 1 | One 5 V supply feeds the ESP32 and the servos through a 1-to-2 cable (common ground); verified for all four get-up directions |