Newest roboclaw_python_library and various changes #26
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SYMPTOM: self.TICKS_PER_METER is always at default value, regardless of value in roboclaw.launch or any other parameter server. CAUSE: A typo in call to rospy.get_param() means it is trying to retrieve a value that does not exist, instead of the intended parameter value. FIX: Add missing 's' to properly retrieve 'ticks_per_meter' value
SYMPTOM: Unpredictable erros occurring at runtime
File "roboclaw_node.py", line 232, in run
rospy.logdebug(" Encoders %d %d" % (enc1, enc2))
TypeError: %d format: a number is required, not NoneType
CAUSE: Error when calling roboclaw.ReadEnc would result in encoder
values 'enc1' or 'enc2' to be None instead of a number. This triggers
TypeError as described above.
FIX: Do exactly what TypeError wants us to do: make sure both 'enc1' and
'enc2' are numbers before trying to format them as numbers for logging.
(Note this does not address root cause of ReadEnc failure, that will be
submitted as a separate fix.)
REFERENCE: Python number check courtesy of StackOverflow: https://stackoverflow.com/questions/3441358/what-is-the-most-pythonic-way-to-check-if-an-object-is-a-number
SYMPTOM: Unpredictable errors when calling roboclaw API, manifesting in several different forms such as "OSError: 11" CAUSE: The roboclaw API is not thread-safe, but we have three different threads potentially calling into the API simultaneously. When this occurs, errors follow. 1. self.run for our '/odom' publisher thread 2. self.cmd_vel_callback as '/cmd_vel' subscriber 3. self.check_vitals running for diagnostics FIX: Use a threading.Lock() object to synchronize usage of roboclaw API object. Thereby ensuring only one thread will be communicating with roboclaw at any given time. REFERENCES: ROS Python API Threading Model https://answers.ros.org/question/9543/rospy-threading-model/ StackOverflow "Semaphores on Python" https://stackoverflow.com/questions/31508574/semaphores-on-python
SYMPTOM: When robot turns right, /odom pose orientation turns left. (And vice versa.) However, the odom->base_link transform is correct. CAUSE: Encoder odometry entry point update_publish(enc_left,enc_right) is invoked with update_publish(enc1, enc2). But this is backwards. As per cmd_vel_callback, motor 1 is the right-hand side motor and motor 2 the left-hand side. As a result odometry calculations are reversed. Why does the odom->base_link transform look OK? An earlier change added a negative sign in front of the published transform angle. This only masked the error without fixing the underlying cause, resulting in reversed /odom data and leaving variables like self.last_enc_right holding the wrong values. FIX: Reverse the parameters when calling update_publish so they are correct. And now that the underlying problem is addressed, the negative sign must be removed from the angle when publishing transform.
Fix typo when reading ticks_per_meter parameter
merge changes
- according to docu rev. 5.4 - for firmware 4.1.34
callen5914
approved these changes
Dec 15, 2021
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@sonyccd, even if you don't have time to maintain this project, here is pull request with some changes: