2

MicroPython 2.0 beta 5

Trying to understand how the stalled() function on the motor works. I run a motor at dc of 100, and hold the wheel so that it cannot move.

But the stalled function doesn't fire, indeed whatever I do I don't seem able to get it to return True?

I tried with less power, but still not able to get anything out of this function.

#!/usr/bin/env pybricks-micropython
from pybricks import ev3brick as brick
from pybricks.ev3devices import Motor
from pybricks.parameters import Port, Stop

left_motor = Motor(Port.B) 

speed = 800

# option 1
left_motor.dc(100)

# option 2
#left_motor.run_until_stalled(speed, Stop.HOLD, 100)

while True:
    if left_motor.stalled():
        print("stalled")

If I use option 1: the motor runs, I hold it until it stops, nothing reported. I let go and off it goes again.

If I use option 2: the motor runs, I hold it, it stops. But at no point do I see a report saying it stalled.

nekomatic
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user3069232
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  • What platform are you running MicroPython on, and can you include your MicroPython code in the question please? `stalled` isn't part of base MicroPython so you must be getting this function from some additional library. – nekomatic Aug 29 '19 at 15:47
  • I am running it on the LEGO mindstorms ev3dev.org build with the MicroPython I downloaded from the LEGO website and subsequently updated with apt-get commands. So it is pybricks library I think. I edited the subject line to make it more specific. – user3069232 Aug 29 '19 at 15:49
  • Please post your code... – nekomatic Aug 30 '19 at 08:25
  • @nekomatic I edited the question and included some code. – user3069232 Aug 31 '19 at 18:08
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    OK, I've found [the docs for the library](https://education.lego.com/en-us/support/mindstorms-ev3/python-for-ev3) you seem to be using and if you've read what it says there about `stalled()` and `run_until_stalled()` then I've no further ideas. Have you tried the [ev3dev2](https://python-ev3dev.readthedocs.io/en/ev3dev-stretch/index.html) library instead? I'm deleting my answer as it clearly wasn't correct. – nekomatic Sep 05 '19 at 15:31
  • I did try using Python3, but switched too microPython since it is significantly faster, the chosen path of the LEGO company. Which gives me another idea, I ask LEGO support the question. Thanks @nekomatic. – user3069232 Sep 06 '19 at 17:10

1 Answers1

1

A motor is stalled when it can't reach its target speed or angle, despite applying the maximum duty cycle.

Your example can be adapted like this:

#!/usr/bin/env pybricks-micropython
from pybricks.ev3devices import Motor
from pybricks.parameters import Port
from pybricks.tools import wait

# Initialize the motor
left_motor = Motor(Port.B)

# Start running the motor at 500 deg/s
left_motor.run(500)

# Do nothing until we are stalled
while not left_motor.stalled():
    wait(10)

# Stop the motor
left_motor.stop()

This example is equivalent to the one-liner left_motor.run_until_stalled(500). The manual approach can be useful if you want to extend it to multiple motors.

The dc() method in the question does not set a target speed or angle; it sets the duty cycle directly, so there is no stall information.

Note: the left_motor.stalled() method is instead accessible through left_motor.control.stalled() as of Pybricks version Pybricks 2.0. It is in public beta only as of March 2020, so I'm not sure the version reported in the original post in August 2019 is correct.

Laurens Valk
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