Bug fix: fix setting different learning rates between backbone and ma…

…in model in ACT policy (#280)

lerobot/scripts/train.py

@@ -53,12 +53,14 @@ def make_optimizer_and_scheduler(cfg, policy):
                 "params": [
                     p
                     for n, p in policy.named_parameters()
-                    if not n.startswith("backbone") and p.requires_grad
+                    if not n.startswith("model.backbone") and p.requires_grad
                 ]
             },
             {
                 "params": [
-                    p for n, p in policy.named_parameters() if n.startswith("backbone") and p.requires_grad
+                    p
+                    for n, p in policy.named_parameters()
+                    if n.startswith("model.backbone") and p.requires_grad
                 ],
                 "lr": cfg.training.lr_backbone,
             },

tests/test_policies.py

@@ -30,6 +30,7 @@
 from lerobot.common.policies.normalize import Normalize, Unnormalize
 from lerobot.common.policies.policy_protocol import Policy
 from lerobot.common.utils.utils import init_hydra_config
+from lerobot.scripts.train import make_optimizer_and_scheduler
 from tests.scripts.save_policy_to_safetensors import get_policy_stats
 from tests.utils import DEFAULT_CONFIG_PATH, DEVICE, require_cpu, require_env, require_x86_64_kernel
 
@@ -174,6 +175,33 @@ def test_policy(env_name, policy_name, extra_overrides):
     env.step(action)
 
 
+def test_act_backbone_lr():
+    """
+    Test that the ACT policy can be instantiated with a different learning rate for the backbone.
+    """
+    cfg = init_hydra_config(
+        DEFAULT_CONFIG_PATH,
+        overrides=[
+            "env=aloha",
+            "policy=act",
+            f"device={DEVICE}",
+            "training.lr_backbone=0.001",
+            "training.lr=0.01",
+        ],
+    )
+    assert cfg.training.lr == 0.01
+    assert cfg.training.lr_backbone == 0.001
+
+    dataset = make_dataset(cfg)
+    policy = make_policy(hydra_cfg=cfg, dataset_stats=dataset.stats)
+    optimizer, _ = make_optimizer_and_scheduler(cfg, policy)
+    assert len(optimizer.param_groups) == 2
+    assert optimizer.param_groups[0]["lr"] == cfg.training.lr
+    assert optimizer.param_groups[1]["lr"] == cfg.training.lr_backbone
+    assert len(optimizer.param_groups[0]["params"]) == 133
+    assert len(optimizer.param_groups[1]["params"]) == 20
+
+
 @pytest.mark.parametrize("policy_name", available_policies)
 def test_policy_defaults(policy_name: str):
     """Check that the policy can be instantiated with defaults."""