fix(robots): retry SO follower/leader bus reads on transient Feetech errors (#4207)

* fix(robots): retry SO follower/leader bus reads on transient Feetech errors

SO-100/SO-101 teleoperation aborts when a sync_read of Present_Position
returns a corrupted status packet ("Incorrect status packet!"), which the
Feetech bus emits intermittently under load. The read path already supports
a num_retry argument but the SO follower and leader never used it, so a single
transient failure crashed the control loop.

Add a max_read_retry config option (default 3) to SOFollowerConfig and
SOLeaderConfig and forward it to every Present_Position sync_read. Retries are
immediate and only happen on failure, so the steady-state read cost is
unchanged; set max_read_retry=0 to restore the previous behavior.

Fixes #3131

* chore(robots): change defaults

---------

Co-authored-by: isaka1022 <isaka1022@gmail.com>

tests/motors/test_feetech.py

@@ -294,6 +294,19 @@ def test__sync_read(addr, length, ids_values, mock_motors, dummy_motors):
     assert read_values == ids_values
 
 
+def test__sync_read_retries_after_transient_failure(mock_motors, dummy_motors):
+    addr, length, ids_values = (10, 4, {1: 1337})
+    stub = mock_motors.build_sync_read_stub(addr, length, ids_values, num_invalid_try=1)
+    bus = FeetechMotorsBus(port=mock_motors.port, motors=dummy_motors)
+    bus.connect(handshake=False)
+
+    read_values, read_comm = bus._sync_read(addr, length, list(ids_values), num_retry=1)
+
+    assert read_comm == scs.COMM_SUCCESS
+    assert read_values == ids_values
+    assert mock_motors.stubs[stub].calls == 2
+
+
 @pytest.mark.parametrize("raise_on_error", (True, False))
 def test__sync_read_comm(raise_on_error, mock_motors, dummy_motors):
     addr, length, ids_values = (10, 4, {1: 1337})

tests/robots/test_so100_follower.py

@@ -49,7 +49,7 @@ def _make_bus_mock() -> MagicMock:
 
 
 @pytest.fixture
-def follower():
+def follower(tmp_path):
     bus_mock = _make_bus_mock()
 
     def _bus_side_effect(*_args, **kwargs):
@@ -71,7 +71,7 @@ def follower():
         ),
         patch.object(SO100Follower, "configure", lambda self: None),
     ):
-        cfg = SO100FollowerConfig(port="/dev/null")
+        cfg = SO100FollowerConfig(port="/dev/null", calibration_dir=tmp_path)
         robot = SO100Follower(cfg)
         yield robot
         if robot.is_connected:
@@ -99,6 +99,27 @@ def test_get_observation(follower):
         assert obs[f"{motor}.pos"] == idx
 
 
+def test_get_observation_uses_read_retries(follower):
+    # Feetech buses can intermittently fail a sync_read; the follower should forward the configured
+    # retry count so transient failures don't abort the control loop (see #3131).
+    follower.config.num_read_retries = 7
+    follower.connect()
+    follower.get_observation()
+
+    follower.bus.sync_read.assert_called_once_with("Present_Position", num_retry=7)
+
+
+def test_send_action_uses_read_retries(follower):
+    follower.config.max_relative_target = 10.0
+    follower.config.num_read_retries = 7
+    follower.connect()
+
+    action = {f"{motor}.pos": value * 10 for value, motor in enumerate(follower.bus.motors, 1)}
+    follower.send_action(action)
+
+    follower.bus.sync_read.assert_called_once_with("Present_Position", num_retry=7)
+
+
 def test_send_action(follower):
     follower.connect()