Gymnasium/docs/environments/box2d/bipedal_walker.md

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title: Bipedal Walker
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# Bipedal Walker

```{figure} ../../_static/videos/box2d/bipedal_walker.gif 
:width: 200px
:name: bipedal_walker
```

This environment is part of the <a href='..'>Box2D environments</a>. Please read that page first for general information.

|   |   |
|---|---|
| Action Space | Box(-1.0, 1.0, (4,), float32) |
| Observation Shape | (24,) |
| Observation High | [3.14 5.   5.   5.   3.14 5.   3.14 5.   5.   3.14 5.   3.14 5.   5.  1.   1.   1.   1.   1.   1.   1.   1.   1.   1.  ] |
| Observation Low | [-3.14 -5.   -5.   -5.   -3.14 -5.   -3.14 -5.   -0.   -3.14 -5.   -3.14  -5.   -0.   -1.   -1.   -1.   -1.   -1.   -1.   -1.   -1.   -1.   -1.  ] |
| Import | `gymnasium.make("BipedalWalker-v3")` | 


### Description
This is a simple 4-joint walker robot environment.
There are two versions:
- Normal, with slightly uneven terrain.
- Hardcore, with ladders, stumps, pitfalls.

To solve the normal version, you need to get 300 points in 1600 time steps.
To solve the hardcore version, you need 300 points in 2000 time steps.

A heuristic is provided for testing. It's also useful to get demonstrations
to learn from. To run the heuristic:
```
python gymnasium/envs/box2d/bipedal_walker.py
```

### Action Space
Actions are motor speed values in the [-1, 1] range for each of the
4 joints at both hips and knees.

### Observation Space
State consists of hull angle speed, angular velocity, horizontal speed,
vertical speed, position of joints and joints angular speed, legs contact
with ground, and 10 lidar rangefinder measurements. There are no coordinates
in the state vector.

### Rewards
Reward is given for moving forward, totaling 300+ points up to the far end.
If the robot falls, it gets -100. Applying motor torque costs a small
amount of points. A more optimal agent will get a better score.

### Starting State
The walker starts standing at the left end of the terrain with the hull
horizontal, and both legs in the same position with a slight knee angle.

### Episode Termination
The episode will terminate if the hull gets in contact with the ground or
if the walker exceeds the right end of the terrain length.

### Arguments
To use to the _hardcore_ environment, you need to specify the
`hardcore=True` argument like below:
```python
import gymnasium
env = gymnasium.make("BipedalWalker-v3", hardcore=True)
```

### Version History
- v3: returns closest lidar trace instead of furthest;
    faster video recording
- v2: Count energy spent
- v1: Legs now report contact with ground; motors have higher torque and
    speed; ground has higher friction; lidar rendered less nervously.
- v0: Initial version


<!-- ### References -->

### Credits
Created by Oleg Klimov