Add section 5.4.2 - Code Example: Training SmolVLA

sections/05_foundation_models.tex

@@ -239,3 +239,8 @@ \subsubsection{Code Example: Using SmolVLA}
 \begin{pbox}[label={ex:using-smolvla}]{Using SmolVLA \\ \url{https://github.com/fracapuano/robot-learning-tutorial/blob/main/snippets/ch5/02_using_smolvla.py}}
     \lstinputlisting[language=python]{snippets/ch5/02_using_smolvla.py}
 \end{pbox}
+
+\subsubsection{Code Example: Training SmolVLA}
+\begin{pbox}[label={ex:training-smolvla}]{Training SmolVLA \\ \url{https://github.com/fracapuano/robot-learning-tutorial/blob/main/snippets/ch5/03_training_smolvla.py}}
+    \lstinputlisting[language=python]{snippets/ch5/03_training_smolvla.py}
+\end{pbox}

snippets/ch5/03_training_smolvla.py

@@ -0,0 +1,206 @@
+from pathlib import Path
+
+import torch
+
+from lerobot.datasets.lerobot_dataset import LeRobotDataset, LeRobotDatasetMetadata
+from lerobot.policies.factory import make_pre_post_processors
+from lerobot.policies.smolvla.configuration_smolvla import SmolVLAConfig
+from lerobot.policies.smolvla.modeling_smolvla import SmolVLAPolicy
+
+
+# Output directory for saving the trained model
+output_directory = Path("outputs/train/my_smolvla")
+output_directory.mkdir(parents=True, exist_ok=True)
+
+device = torch.device("mps")  # or "cuda" or "cpu"
+
+# Replace with your custom dataset repo_id (e.g., "${HF_USER}/mydataset")
+dataset_id = "lerobot/svla_so100_pickplace"
+
+# Model configuration
+# Option 1: Load from a pretrained SmolVLA checkpoint (recommended for fine-tuning)
+pretrained_model_id = "lerobot/smolvla_base"
+load_from_pretrained = True  # Set to False to train from scratch
+
+# Option 2: Train from scratch (only if you have a large dataset and computational resources)
+# This will initialize the model with a pretrained VLM backbone but random action expert
+# load_from_pretrained = False
+
+# Load dataset metadata to get features and statistics
+print(f"Loading dataset metadata from {dataset_id}...")
+dataset_metadata = LeRobotDatasetMetadata(dataset_id)
+
+if load_from_pretrained:
+    print(f"Loading pretrained model from {pretrained_model_id}...")
+    policy = SmolVLAPolicy.from_pretrained(pretrained_model_id)
+
+    # Create rename map to match dataset keys to model's expected keys
+    rename_map = {
+        "observation.images.top": "observation.images.camera1",
+        "observation.images.wrist": "observation.images.camera2",
+    }
+
+    # Create preprocessor and postprocessor with dataset statistics
+    # This is important for normalizing inputs/outputs to match your dataset
+    preprocessor, postprocessor = make_pre_post_processors(
+        policy.config,
+        pretrained_path=pretrained_model_id,
+        preprocessor_overrides={
+            "device_processor": {"device": str(device)},
+            "rename_observations_processor": {"rename_map": rename_map},
+            "normalizer_processor": {
+                "stats": dataset_metadata.stats,
+                "features": {**policy.config.input_features, **policy.config.output_features},
+                "norm_map": policy.config.normalization_mapping,
+            },
+        },
+        postprocessor_overrides={
+            "unnormalizer_processor": {
+                "stats": dataset_metadata.stats,
+                "features": policy.config.output_features,
+                "norm_map": policy.config.normalization_mapping,
+            },
+        },
+    )
+else:
+    print("Initializing new SmolVLA model from scratch...")
+    # Note: Training from scratch requires careful configuration
+    # The input/output features must match your dataset structure
+    from lerobot.configs.types import FeatureType
+    from lerobot.datasets.utils import dataset_to_policy_features
+
+    features = dataset_to_policy_features(dataset_metadata.features)
+    output_features = {key: ft for key, ft in features.items() if ft.type is FeatureType.ACTION}
+    input_features = {key: ft for key, ft in features.items() if key not in output_features}
+
+    cfg = SmolVLAConfig(input_features=input_features, output_features=output_features)
+    cfg.load_vlm_weights = True  # Load pretrained VLM backbone
+    policy = SmolVLAPolicy(cfg)
+
+    preprocessor, postprocessor = make_pre_post_processors(
+        cfg, dataset_stats=dataset_metadata.stats
+    )
+
+# Move policy to the specified device
+policy.train()
+policy.to(device)
+
+
+def make_delta_timestamps(delta_indices: list[int] | None, fps: int) -> list[float]:
+    """Convert delta indices to delta timestamps based on dataset FPS."""
+    if delta_indices is None:
+        return [0]
+    return [i / fps for i in delta_indices]
+
+
+# SmolVLA expects action sequences of length chunk_size (default 50)
+# and single observation frames (n_obs_steps=1)
+delta_timestamps = {
+    "action": make_delta_timestamps(policy.config.action_delta_indices, dataset_metadata.fps),
+}
+
+# Add delta timestamps for image features that actually exist in the dataset
+dataset_image_keys = [k for k in dataset_metadata.features.keys() if "image" in k.lower()]
+delta_timestamps |= {
+    k: make_delta_timestamps(policy.config.observation_delta_indices, dataset_metadata.fps)
+    for k in dataset_image_keys
+}
+
+# Add delta timestamp for state if present
+if "observation.state" in dataset_metadata.features:
+    delta_timestamps["observation.state"] = make_delta_timestamps(
+        policy.config.observation_delta_indices, dataset_metadata.fps
+    )
+
+# Load the dataset with appropriate delta timestamps
+print(f"Loading dataset {dataset_id}...")
+dataset = LeRobotDataset(dataset_id, delta_timestamps=delta_timestamps)
+print(f"Dataset loaded: {dataset.num_episodes} episodes, {dataset.num_frames} frames")
+
+# Training configuration
+batch_size = 64  # Adjust based on your GPU memory (64 works well for most GPUs)
+training_steps = 20000  # Number of training steps (increase for better performance)
+log_freq = 100  # Log every N steps
+
+# Create optimizer and scheduler using SmolVLA's preset configurations
+optimizer = policy.config.get_optimizer_preset().build(policy.parameters())
+lr_scheduler = policy.config.get_scheduler_preset().build(optimizer, num_training_steps=training_steps)
+
+# Create dataloader for offline training
+dataloader = torch.utils.data.DataLoader(
+    dataset,
+    batch_size=batch_size,
+    shuffle=True,
+    pin_memory=device.type == "cuda",
+    drop_last=True,
+    num_workers=4,  # Adjust based on your system
+)
+
+print(f"\nStarting training for {training_steps} steps...")
+print(f"Batch size: {batch_size}")
+print(f"Device: {device}")
+print(f"Output directory: {output_directory}")
+print("-" * 80)
+
+# Training loop
+step = 0
+done = False
+while not done:
+    for batch in dataloader:
+        # Preprocess the batch (normalization, tokenization, etc.)
+        batch = preprocessor(batch)
+
+        # Forward pass: compute loss
+        loss, output_dict = policy.forward(batch)
+
+        # Backward pass and optimization
+        loss.backward()
+        optimizer.step()
+        optimizer.zero_grad()
+
+        # Update learning rate
+        if lr_scheduler is not None:
+            lr_scheduler.step()
+
+        # Logging
+        if step % log_freq == 0:
+            current_lr = optimizer.param_groups[0]["lr"]
+            print(
+                f"Step: {step}/{training_steps} | "
+                f"Loss: {loss.item():.4f} | "
+                f"LR: {current_lr:.2e}"
+            )
+
+        step += 1
+        if step >= training_steps:
+            done = True
+            break
+
+print("-" * 80)
+print("Training completed!")
+
+# Save the trained model
+print(f"\nSaving model to {output_directory}...")
+policy.save_pretrained(output_directory)
+preprocessor.save_pretrained(output_directory)
+postprocessor.save_pretrained(output_directory)
+print("Model saved successfully!")
+
+# Optional: Push to Hugging Face Hub
+# Uncomment and update with your Hugging Face username
+push_to_hub = False  # Set to True to push to Hub
+hub_repo_id = "YOUR_HF_USERNAME/my_smolvla_so101"  # Replace with your repo ID
+
+if push_to_hub:
+    print(f"\nPushing model to Hugging Face Hub: {hub_repo_id}...")
+    policy.push_to_hub(hub_repo_id)
+    preprocessor.push_to_hub(hub_repo_id)
+    postprocessor.push_to_hub(hub_repo_id)
+    print(f"Model pushed to: https://huggingface.co/{hub_repo_id}")
+
+print("\n" + "=" * 80)
+print("Training complete! Next steps:")
+print("1. Test the model with: examples/tutorial/smolvla/using_smolvla_example.py")
+print(f"2. Update model_id in the script to: {output_directory}")
+print("3. Deploy on your SO101 robot!")
+print("=" * 80)