Coding for telemetry

[Isha-Dave]

My team would like to write a code to get robot state and attachment motor data when robot is finishing missions on the field. Any ideas on how to go about this please? We are using micropython

[dlech]

Since you probably can't have a computer connected during a mission, I suggest to use hub.system.storage(). Anything you save here will persist after the program ends and even after power off (assuming proper shutdown). They you can write a separate program to retrieve and print the data in the terminal later.

https://docs.pybricks.com/en/stable/hubs/primehub.html#pybricks.hubs.PrimeHub.system.storage

[Isha-Dave]

Thank you. The team wanted something simple like executing a series of print statements wrapped in a function that runs a fixed interval of time (eg every 100 ms). This can execute in parallel with the robot doing the missions. They want to understand what is happening with robot state while connected to the conputer. They can generate this data to analyse robot behaviour when practicing and debuggibg their runs.

[dlech]

Printing while running can be tricky. Printing takes time, so it can affect the performance of your robot. If you limit it to printing 30 characters or less every 100 ms, the impact should be negligible. But much more than that is almost sure to cause problems.

Another approach instead of printing while running is to log data to a list, then when the mission ends, print the list. You could wrap your whole program in a try:/finally: block to make sure that it prints even if there was an unhandled exception.

# imports and such
...

log = []

def my_func(x):
    log.append(f"x={x}")
    # do something with x
    ...

try:
    # main program goes here
    ...
finally:
    for line in log:
        print(line)

If a function logs too much, you could use a counter or timer to rate-limit calling append().

class RateLimitedLogger:
    def __init__(self, interval_ms):
        self._ms = interval_ms
        self._timer = StopWatch()

    def __call__(self, data):
        if self._timer.time() < self._ms:
            # too soon - don't log
            return

        log.append(data)
        self._timer.reset()

my_func_log= RateLimitedLogger(100)

def my_func(x):
    # only logs at most every 100ms
    my_func_log(f"x={x}")
    # do something with x
    ...

# try/finally as above
...

[Isha-Dave]

Thank you, again! Good to know the print character limit before performance impact. Will work with the team to implelent this.