# Quadruped Assembly

Chapter 13 drives an 8-servo quadruped from your own OS.

```{figure} ../_static/quadruped_walk.gif
:name: fig-quadruped-walk
:width: 80%

The quadruped walking on your own OS, driving 8 servos (1.5x speed)
```

| Item | Qty | Notes |
|---|---|---|
| FEETECH STS3215 serial bus servo (12V) | 8 | [Akizuki Denshi 130969](https://akizukidenshi.com/catalog/g/g130969/) |
| Bus servo driver board (Waveshare 25514) | 1 | [Akizuki Denshi 131227](https://akizukidenshi.com/catalog/g/g131227/) |
| 12V 5A AC adapter | 1 | enough for walking too |
| 3D-printed body & legs | 1 set | STL downloads below |
| Arduino UNO R4 WiFi | 1 | |

::::{grid} 1 1 2 2
:gutter: 3

:::{grid-item-card} 🛒 Bill of materials and where to buy
:link: bom
:link-type: doc

8 STS3215 servos + driver board + power supply, **about ¥35,100**. Links to the
shop pages, choosing a battery, and 3D-printing settings.
:::

:::{grid-item-card} 🔧 Assembly (3D viewer)
:link: assembly
:link-type: doc

Step through the assembly as a 3D animation in the browser. A PDF version is
available too.
:::

:::{grid-item-card} 🚶 Learning to walk (reinforcement learning)
:link: walk
:link-type: doc

The training side that did not fit in the book, with a MuJoCo (physics simulator)
simulation of the trained policy (the learned neural network that decides how the
robot walks) in the browser.
:::

:::{grid-item-card} 🧠 Training the policy yourself
:link: train
:link-type: doc

Retrain with different rewards or speed limits. **Works end to end on Google Colab
(Google's service for running Python in the browser) on its free T4 (a GPU model)
even without a GPU of your own.**
:::

:::{grid-item-card} 🔁 Train in Genesis, walk in MuJoCo
:link: sim2sim
:link-type: doc

Train the same task in a different physics simulator, Genesis, and walk the policy in
MuJoCo in the browser (sim2sim), with the same policy measured in both simulators.
:::

:::{grid-item-card} 🧭 Balancing with an IMU
:link: imu
:link-type: doc

Put an IMU (a sensor for tilt and rotation rate) on the body and walk with a policy
trained on it. It braces with its legs to recover from pushes and keeps standing
while stopped.
:::

:::{grid-item-card} 🦿 Building with Kondo Kagaku KRS servos
:link: krs
:link-type: doc

A version built with KRS-3302 ICS servos and an RCB-4mini instead of the STS3215.
Setting IDs with the Dual USB Adapter, aligning the zero point, assembling with the 3D
viewer, and wiring on a single AC adapter or battery.
:::
::::

```{toctree}
:hidden:

bom
assembly
walk
train
sim2sim
imu
krs
krs_bom
```

## STL downloads

Print quantities: body ×1, bracket ×4, link ×4 (left and right legs use
the same parts). Units are millimeters.

```{raw} html
<ul>
  <li><a href="../../assembly/quadruped/stl/body.stl">body.stl</a> (×1, 230 × 110 × 50 mm)</li>
  <li><a href="../../assembly/quadruped/stl/bracket_outline.stl">bracket_outline.stl</a> (×4, 128 × 52 × 12 mm)</li>
  <li><a href="../../assembly/quadruped/stl/leg_link1.stl">leg_link1.stl</a> (×4, 80 × 52 × 26 mm)</li>
  <li><a href="../../assembly/quadruped/stl/body.3mf">body.3mf</a> — Bambu Studio project, body plate, author-tested settings (X1C, 0.28 mm, ABS)</li>
  <li><a href="../../assembly/quadruped/stl/leg_parts.3mf">leg_parts.3mf</a> — Bambu Studio project, all 8 leg parts</li>
</ul>
```

## Photos

::::{grid} 2 3 3 3
:gutter: 2

:::{grid-item}

```{figure} ../_static/quadruped_parts.jpg
:target: ../_static/quadruped_parts.jpg
:alt: All parts: 9 printed parts, 8 STS3215 servos, and the bundled screws

All parts: 9 printed parts, 8 STS3215 servos, and the bundled screws
```

:::
:::{grid-item}

```{figure} ../_static/quadruped_body_servo.jpg
:target: ../_static/quadruped_body_servo.jpg
:alt: Body with four servos fixed

Body with four servos fixed
```

:::
:::{grid-item}

```{figure} ../_static/quadruped_legs_x4.jpg
:target: ../_static/quadruped_legs_x4.jpg
:alt: Four servos with leg brackets attached

Four servos with leg brackets attached
```

:::
:::{grid-item}

```{figure} ../_static/quadruped_driver_board.jpg
:target: ../_static/quadruped_driver_board.jpg
:alt: Driver board: A/B jumper (yellow), USB Type-C and DC jack

Driver board: A/B jumper (yellow), USB Type-C and DC jack
```

:::
::::

## Interactive assembly guide

An interactive 3D assembly viewer shows every step as an animation:

```{raw} html
<p><a href="../../assembly/quadruped/index.html?lang=en" target="_blank" rel="noopener">
Open the 3D assembly viewer ↗</a></p>
```