Playing sound from balance bot

[dsplaisted]

Hi,

I've modified the balance bot code found here to let the bot be controlled by an XBox controller. That works well.

Now I'd like the bot to be able to play sounds. To do this, I think I need one coroutine making the hub.speaker.play_notes calls while another one runs the main balance loop. So I added an async main() method around the main loop. I added an await to the last line, ie await wait(DT). However, that makes the balance bot fall over. I'm guessing that the context switching for the await takes too long.

So I tried making my own wait implementation instead:

w = StopWatch()
while (w.time() < DT):
    pass

The robot does a better job balancing in that case, but it never yields execution so the sounds don't play. So I tried yielding execution every 100 ms (where await_watch is a StopWatch created outside of the loop):

w = StopWatch()
while (w.time() < DT):
    pass

if (await_watch.time() > 100):
    await wait(1)
    await_watch.reset()

This seems to work decently well, though I'm not sure if it balances quite as well as the non-async version.

My solution seems pretty hacky though. Is there a better way to handle this?

Thanks!

[dlech]

Can you share the full Python script?

---

w = StopWatch()
while (w.time() < DT):
    pass

This makes a blocking timer because there is no await in the loop, so this can cause problems in a multitasking program.

---

It doesn't look like it is documented, but run_task() has a builtin time delay in the loop. The default is 10 ms. So this could be throwing things off since the original script was tuned for a 5ms loop.

For this particular application, it might be best to disable the main loop delay by setting it to 0. Maybe something like this?

from pybricks.hubs import InventorHub
from pybricks.pupdevices import Motor, ColorSensor
from pybricks.parameters import Port, Direction
from pybricks.tools import wait, StopWatch
from pybricks.geometry import Axis

# Initialize motors.
left = Motor(Port.C, Direction.COUNTERCLOCKWISE)
right = Motor(Port.D)
left.reset_angle(0)
right.reset_angle(0)

# Initialize hub and color sensor.
# You can also use the TechnicHub and/or the ColorDistanceSensor
# instead.
hub = InventorHub()
sensor = ColorSensor(Port.A)


async def balance():
    # Initialize position buffer for speed calculation.
    DT = 5
    window = 300 // DT
    buf = [0] * window
    idx = 0
    angle = 0
    DRIVE_SPEED = 300
    PAUSE = 5000

    # Timer to generate reference position.
    watch = StopWatch()

    while True:
        # Get angular rate and estimated angle.
        rate = hub.imu.angular_velocity(Axis.Y)
        angle += rate * DT / 1000

        # Get motor position.
        position = (left.angle() + right.angle()) / 2

        # Calculate motor speed.
        speed = (position - buf[idx]) / (window * DT) * 1000
        buf[idx] = position
        idx = (idx + 1) % window

        # Calculate reference position, which just grows linearly with
        # time.
        reference = -max(watch.time() - PAUSE, 0) / 1000 * DRIVE_SPEED

        # Calculate duty cycle.
        diff = position - reference
        duty = 0.018 * rate + 19 * angle + 0.45 * diff + 0.16 * speed

        # Account for battery level and type.
        duty *= 7200 / hub.battery.voltage()

        # Calculate steering.
        reflection = await sensor.reflection()
        steering = (reflection - 28) * 0.6

        # Apply duty cycle for balancing and steering.
        left.dc(duty + steering)
        right.dc(duty - steering)

        await wait(DT)

async def sound():
    # TODO - replace with actual code
    while True:
        await wait(1)

async def main():
    await multitask(balance(), sound())

run_task(main(), loop_time=0)

[dsplaisted]

Thanks. I tried looptime=0 and loop_time=1 with the simple wait statement, but the robot would still appear to try to balance but fall over. Here's my current code, which more or less works: https://gist.github.com/dsplaisted/b4a4032e1115b80e73c5c36a9baae7d8

[dlech]

Another FYI, the first fix wasn't quite right, resulting in crashes when loop_time=0. That should be fixed in build-3501 and newer.

[dsplaisted]

Hi, I finally got around to installing a nightly firmware to test this (build 3544). When I tried my program, I got TypeError: extra keyword arguments given for this line:

run_task(main(), loop_time=0)

After removing loop_time=0 (and switching back to await wait(DT) instead of my workaround code), the robot seems to balance well. Is the loop_time argument no longer supported or needed?

Thanks!

[BertLindeman]

updated in build 3510

Commit Drop run_loop arg

[dsplaisted]

Thanks for the help folks! We used this for my son to tell a fun children's story at our church: https://youtu.be/_-ntSqQ62Ps

[laurensvalk]

That's awesome, thanks for sharing!