Autonomous Questions

In preparation for next year, my team is working on some autonomous code for the AVR drone. However, we’re getting stuck at the basic parts.

I wrote a simple variation on the provided script, to flash the led strip. However, the mqtt message is not being sent and nothing changes. The debug statements before and after the message are being sent. I’m not sure quite what’s wrong.

Other clarifying question: With the unedited, how do I trigger the open_servo() function? I see it defined but never called.

I’m definitely seeing the same thing when running your sample code in my sandbox. Let me chat with @nathan to see if he can shed some light on this.

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Let me try my best to explain what’s going on.

While the __init__ method of the MQTTModule class (what you’re calling with super().__init__()) connects to the MQTT broker, it does not start what is called the “event loop”. The event loop is an infinite loop that processes MQTT messages. This includes receiving incoming messages, and running callback functions defined in the topic_map, but at the same time, it also deals with sending messages as well. Without this event loop, nothing happens besides connecting to the broker.

In order to start the event loop, there are two options.

  1. The method. This starts the infinite loop, and prevents any more code from ever running. This is ideal for when you want your sandbox code to always be responding to incoming messages, like the example I made.
  2. The box.run_non_blocking() method. This starts the event loop in the background, and allows more code to run. This is great for when you have code that needs to run independently of incoming messages, like your code. This is how the software that gets data from the ZED Mini tracking camera works. When you do this however, you need to have some kind of infinite loop running, so your code doesn’t reach the end and stop executing.

Putting all of that together, this is how I would rewrite your example to work:

import time

from bell.avr.mqtt.client import MQTTModule
from bell.avr.mqtt.payloads import AvrPcmSetBaseColorPayload
from loguru import logger

class Sandbox(MQTTModule):
    def __init__(self) -> None:
        logger.debug("Class initialized")

    def hello_world(self) -> None:
        logger.debug("Hello world")

        payload = AvrPcmSetBaseColorPayload(wrgb=(0, 100, 0, 0))
        self.send_message("avr/pcm/set_base_color", payload)

        logger.debug("Light changed")

if __name__ == "__main__":
    box = Sandbox()


    while True:

To answer your clarifying question, the open_servo function cannot be called from the unedited It needs to be called in the callback to some incoming message (like, if I see this AprilTag, open this servo). I was trying not to give too much away and leave it as an exercise to the reader.

I know this is a month old, but I added an example of this, and tried to explain why better in the new Python libraries documentation:

It’s still a work in progress and subject to change.

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Woo! That’ll be so helpful to everyone this year. It’s too bad that so few teams dipped into auton last year, and this makes it way more accessible.