(#836) Rotation scan plan gets accl from motor

src/artemis/experiment_plans/rotation_scan_plan.py

@@ -52,7 +52,8 @@ def create_devices() -> dict[str, Device]:
 
 DEFAULT_DIRECTION = RotationDirection.NEGATIVE
 DEFAULT_MAX_VELOCITY = 120
-TIME_TO_VELOCITY_S = 0.15
+# Use a slightly larger time to accceleration than EPICS as it's better to be cautious
+ACCELERATION_MARGIN = 1.5
 
 
 def setup_sample_environment(
@@ -180,12 +181,12 @@ def rotation_scan_plan(
     speed_for_rotation_deg_s = image_width_deg / exposure_time_s
     LOGGER.info(f"calculated speed: {speed_for_rotation_deg_s} deg/s")
 
-    # TODO get this from epics instead of hardcoded - time to velocity
-    # https://github.com/DiamondLightSource/python-artemis/issues/836
-    acceleration_offset = TIME_TO_VELOCITY_S * speed_for_rotation_deg_s
+    motor_time_to_speed = yield from bps.rd(smargon.omega.acceleration)
+    motor_time_to_speed *= ACCELERATION_MARGIN
+    acceleration_offset = motor_time_to_speed * speed_for_rotation_deg_s
     LOGGER.info(
         f"calculated rotation offset for acceleration: at {speed_for_rotation_deg_s} "
-        f"deg/s, to take {TIME_TO_VELOCITY_S} s = {acceleration_offset} deg"
+        f"deg/s, to take {motor_time_to_speed} s = {acceleration_offset} deg"
     )
 
     shutter_opening_degrees = (

src/artemis/experiment_plans/tests/test_rotation_scan_plan.py

@@ -517,3 +517,48 @@ def test_ispyb_deposition_in_plan(
     assert beamsize_x == test_bs_x
     assert beamsize_y == test_bs_y
     assert exposure == test_exp_time
+
+
+@patch(
+    "artemis.experiment_plans.rotation_scan_plan.move_to_start_w_buffer", autospec=True
+)
+def test_acceleration_offset_calculated_correctly(
+    mock_move_to_start: MagicMock,
+    RE: RunEngine,
+    test_rotation_params: RotationInternalParameters,
+    smargon: Smargon,
+    zebra: Zebra,
+    eiger: EigerDetector,
+    attenuator: Attenuator,
+    detector_motion: DetectorMotion,
+    backlight: Backlight,
+    mock_rotation_subscriptions: RotationCallbackCollection,
+    synchrotron: Synchrotron,
+    s4_slit_gaps: S4SlitGaps,
+    undulator: Undulator,
+    flux: Flux,
+):
+    smargon.omega.acceleration.sim_put(0.2)
+    setup_and_run_rotation_plan_for_tests(
+        RE,
+        test_rotation_params,
+        smargon,
+        zebra,
+        eiger,
+        attenuator,
+        detector_motion,
+        backlight,
+        mock_rotation_subscriptions,
+        synchrotron,
+        s4_slit_gaps,
+        undulator,
+        flux,
+    )
+
+    expected_start_angle = (
+        test_rotation_params.artemis_params.detector_params.omega_start
+    )
+
+    mock_move_to_start.assert_called_once_with(
+        smargon.omega, expected_start_angle, pytest.approx(0.3)
+    )