trifinger_backend: Get camera rate from driver

Instead of hard-coding it in the script, use the new `get_sensor_info()`
method of the driver to get the camera frame rate.

The frame rate is specified for each of the three cameras, but since
they are syncronised, they are all the same, so we can simply take the
value from the first camera in the list.

scripts/trifinger_backend.py

@@ -14,8 +14,6 @@
 import robot_fingers
 
 
-# Frame rate of the cameras
-CAMERA_FPS = 10
 # Control rate of the robot
 ROBOT_RATE_HZ = 1000
 
@@ -128,7 +126,7 @@ def parse_arguments() -> argparse.Namespace:
     # not possible to decide the logger buffer size)
     if (args.robot_logfile or args.camera_logfile) and not args.max_number_of_actions:
         parser.error(
-            "--max-number-of-actions must be specified when using data" " logging."
+            "--max-number-of-actions must be specified when using data logging."
         )
 
     if not args.config_dir.is_dir():
@@ -172,14 +170,17 @@ def main() -> int:
     if cameras_enabled:
         logging.info("Start camera backend")
 
+        camera_driver = CameraDriver("camera60", "camera180", "camera300")
+        # all cameras have the same frame rate, so just use the first one
+        camera_fps = camera_driver.get_sensor_info().camera[0].frame_rate_fps
+
         # make sure camera time series covers at least one second (add some
         # margin to avoid problems)
-        CAMERA_TIME_SERIES_LENGTH = int(CAMERA_FPS * 1.5)
+        camera_time_series_length = int(camera_fps * 1.5)
 
         camera_data = tricamera.MultiProcessData(
-            "tricamera", True, CAMERA_TIME_SERIES_LENGTH
+            "tricamera", True, camera_time_series_length
         )
-        camera_driver = CameraDriver("camera60", "camera180", "camera300")
         camera_backend = tricamera.Backend(camera_driver, camera_data)
 
         logging.info("Camera backend ready.")
@@ -229,7 +230,7 @@ def main() -> int:
         episode_length_s = args.max_number_of_actions / ROBOT_RATE_HZ
         # Compute camera log size based on number of robot actions plus a 10%
         # buffer
-        log_size = int(CAMERA_FPS * episode_length_s * buffer_length_factor)
+        log_size = int(camera_fps * episode_length_s * buffer_length_factor)
 
         logging.info("Initialize camera logger with buffer size %d", log_size)
         camera_logger = tricamera.Logger(camera_data, log_size)