Motor.run_target() raises RuntimeError #786

dlech · 2022-11-10T19:03:43Z

Describe the bug
What is the problem?

After some time, the program below crashes one of the steer.run_target() lines with a RuntimeError. The time is variable but usually less than a minute (pressing buttons on the remote to steer during this time).

Full output:

('technichub', '3.2.0b4', 'v3.2.0b4-34-g51478f08-dirty on 2022-11-10')
steer angle: 102.5
Traceback (most recent call last):
  File "issue785.py", line 53, in <module>
RuntimeError: Unknown error

To reproduce

from pybricks.pupdevices import Motor, Remote
from pybricks.parameters import Port, Direction, Stop, Button, Color
from pybricks.hubs import TechnicHub
from pybricks.tools import wait
from pybricks import version

print(version)

# Initialize the motors.
steer = Motor(Port.C)
front = Motor(Port.D, Direction.COUNTERCLOCKWISE)

# Connect to the remote and set the light on the remote
remote = Remote()
remote.light.on(Color.GREEN)

# Initialize the hub.
hub = TechnicHub()
hub.light.on(Color.GREEN)

# Read the current settings
old_kp, old_ki, old_kd, _, _ = steer.control.pid()

# Set new values
steer.control.pid(kp=old_kp*4, kd=old_kd*0.4)

# Set initial top speed value
top_speed = 100

# Find the steering endpoint on the left and right.
# The middle is in between.
left_end = steer.run_until_stalled(-200, then=Stop.HOLD)
right_end = steer.run_until_stalled(200, then=Stop.HOLD)

# We are now at the right. Reset this angle to be half the difference.
# That puts zero in the middle.
steer.reset_angle((right_end - left_end)/2)
steer.run_target(speed=200, target_angle=0, wait=False)

# Set steering angle for the buggy
steer_angle = (((right_end - left_end)/2)-5)
print('steer angle:',steer_angle)

# Now we can start driving!
while True:
    # Check which buttons are pressed.
    pressed = remote.buttons.pressed()

    # Choose the steer angle based on the right controls.
    if Button.LEFT_PLUS in pressed:
        steer.run_target(1400, -steer_angle, Stop.HOLD, False)
    elif Button.LEFT_MINUS in pressed:
        steer.run_target(1400, steer_angle, Stop.HOLD, False)
    else:
        steer.track_target(0)

    # Top speed controls
    if Button.LEFT in pressed:
        top_speed = 75
    if Button.RIGHT in pressed:
        top_speed = 100   
    if ((Button.RIGHT in pressed) and (Button.LEFT in pressed)):
        top_speed = 40 

    # Choose the drive speed based on the left controls.
    drive_speed = 0
    if Button.RIGHT_PLUS in pressed:
        drive_speed -= top_speed
    if Button.RIGHT_MINUS in pressed:
        drive_speed += top_speed         

    # Apply the selected speed.
    front.dc(drive_speed)

    # Wait.
    wait(10)

Expected behavior
What did you expect to happen instead?

Program should run forever.

The text was updated successfully, but these errors were encountered:

laurensvalk · 2022-11-10T19:06:21Z

Nice find 👍 , I'm happy to look into it.

laurensvalk · 2022-11-10T19:07:01Z

Which motors are connected here? They all have different acceleration profiles, which could be relevant for reproduction.

dlech · 2022-11-10T19:08:08Z

I used the gray medium motors from Robot Inventor for this test.

laurensvalk · 2022-11-10T19:14:00Z

This probably fails in pbio/trajectory.c, where PBIO_ERROR_FAILED indicates an invalid trajectory.

We should be able to do something like:

old_trajectory = steer.control.trajectory()
try:
    steer.run_target(1400, -steer_angle, Stop.HOLD, False)
except:
    print(steer_angle)
    print(old_trajectory)
    print(steer.control.limits())
    print(steer.control.trajectory())

Then we can add the failed case to test/trajectory.c and statically analyse and debug it.

laurensvalk · 2022-11-11T05:55:32Z

For what it's worth, a contributing factor is this. This is an old hack that should no longer be used.

steer.control.pid(kp=old_kp*4, kd=old_kd*0.4)

laurensvalk · 2022-11-11T06:04:41Z

ThisHub variant with debug:

from pybricks.pupdevices import Motor, Remote
from pybricks.parameters import Port, Direction, Stop, Button, Color
from pybricks.hubs import ThisHub
from pybricks.tools import wait
from pybricks import version

print(version)

# Initialize the motors.
steer = Motor(Port.A)
front = Motor(Port.B, Direction.COUNTERCLOCKWISE)

# Connect to the remote and set the light on the remote
remote = Remote()
remote.light.on(Color.GREEN)

# Initialize the hub.
hub = ThisHub()
hub.light.on(Color.GREEN)

# Read the current settings
old_kp, old_ki, old_kd, _, _ = steer.control.pid()

# Set new values
steer.control.pid(kp=old_kp*4, kd=old_kd*0.4)

# Set initial top speed value
top_speed = 100

# Find the steering endpoint on the left and right.
# The middle is in between.
# left_end = steer.run_until_stalled(-200, then=Stop.HOLD)
# right_end = steer.run_until_stalled(200, then=Stop.HOLD)

# We are now at the right. Reset this angle to be half the difference.
# That puts zero in the middle.
# steer.reset_angle((right_end - left_end)/2)
# steer.run_target(speed=200, target_angle=0, wait=False)

# Set steering angle for the buggy
# steer_angle = (((right_end - left_end)/2)-5)
# print('steer angle:',steer_angle)
steer_angle = 167.5

# Now we can start driving!
while True:
    # Check which buttons are pressed.
    pressed = remote.buttons.pressed()


    old_trajectory = steer.control.trajectory()
    try:
        # Choose the steer angle based on the right controls.
        if Button.LEFT_PLUS in pressed:
            steer.run_target(1400, -steer_angle, Stop.HOLD, False)
        elif Button.LEFT_MINUS in pressed:
            steer.run_target(1400, steer_angle, Stop.HOLD, False)
        else:
            steer.track_target(0)
    except RuntimeError:
        print(steer_angle)
        print(old_trajectory)
        print(steer.control.limits())
        print(steer.control.trajectory())
        hub.speaker.beep()

    # Top speed controls
    if Button.LEFT in pressed:
        top_speed = 75
    if Button.RIGHT in pressed:
        top_speed = 100   
    if ((Button.RIGHT in pressed) and (Button.LEFT in pressed)):
        top_speed = 40 

    # Choose the drive speed based on the left controls.
    drive_speed = 0
    if Button.RIGHT_PLUS in pressed:
        drive_speed -= top_speed
    if Button.RIGHT_MINUS in pressed:
        drive_speed += top_speed         

    # Apply the selected speed.
    front.dc(drive_speed)

    # Wait.
    wait(10)

laurensvalk · 2022-11-11T06:05:28Z

Here are two cases:

steer angle: 167.5
167.5
(0, 0, 0, 12, 0, 0, 0, 0, -24, -24, 0, 2000, 2000)
(1080, 2000, 199)
(0, 0, 0, 1, 0, 0, 0, 0, 3, 3, 0, 2000, -2000)

167.5
(0, 0, 0, 12, 0, 0, 0, 0, 24, 24, 0, -2000, -2000)
(1080, 2000, 199)
(0, 0, 0, 1, 0, 0, 0, 0, 3, 3, 0, 2000, -2000)

laurensvalk · 2022-11-11T06:39:53Z

Running with this diff gives a bit more detail:

diff --git a/pybricks/common/pb_type_control.c b/pybricks/common/pb_type_control.c
index b96e5edc..620f9649 100644
--- a/pybricks/common/pb_type_control.c
+++ b/pybricks/common/pb_type_control.c
@@ -213,16 +213,16 @@ STATIC mp_obj_t common_Control_trajectory(mp_obj_t self_in) {
 
     if (pbio_control_is_active(self->control)) {
         parms[0] = mp_obj_new_int(0);
-        parms[1] = mp_obj_new_int(trj->t1 / 10);
-        parms[2] = mp_obj_new_int(trj->t2 / 10);
-        parms[3] = mp_obj_new_int(trj->t3 / 10);
+        parms[1] = mp_obj_new_int(trj->t1);
+        parms[2] = mp_obj_new_int(trj->t2);
+        parms[3] = mp_obj_new_int(trj->t3);
         parms[4] = mp_obj_new_int(0);
-        parms[5] = mp_obj_new_int(trj->th1 / 1000);
-        parms[6] = mp_obj_new_int(trj->th2 / 1000);
-        parms[7] = mp_obj_new_int(trj->th3 / 1000);
-        parms[8] = mp_obj_new_int(trj->w0 / 10);
-        parms[9] = mp_obj_new_int(trj->w1 / 10);
-        parms[10] = mp_obj_new_int(trj->w3 / 10);
+        parms[5] = mp_obj_new_int(trj->th1);
+        parms[6] = mp_obj_new_int(trj->th2);
+        parms[7] = mp_obj_new_int(trj->th3);
+        parms[8] = mp_obj_new_int(trj->w0);
+        parms[9] = mp_obj_new_int(trj->w1);
+        parms[10] = mp_obj_new_int(trj->w3);
         parms[11] = mp_obj_new_int(trj->a0);
         parms[12] = mp_obj_new_int(trj->a2);
         return mp_obj_new_tuple(13, parms);

laurensvalk · 2022-11-11T06:47:21Z

steer angle: 136.0
136.0
(0, 0, 0, 110, 0, 0, 0, 121, 220, 220, 0, -2000, -2000)
(1080, 2000, 199)
(0, -9, -9, -9, 0, 0, 0, 1, 18, 0, 0, 2000, -2000)

0   = 0,
t1  =-9,
t2  =-9,
t3  =-9,
0   = 0,
th1 = 0,
th2 = 0,
th3 = 1,
w0  = 18,
w1  = 0,
w3  = 0,
a0  = 2000,
a2  =-2000

The error is nagative time t1 of -9 (or 0 when rounded) so it fails at:

https://github.com/pybricks/pybricks-micropython/blob/51478f08b392110bc0ea6cc9c5940266c254d93c/lib/pbio/src/trajectory.c#L469

Fix incorrect acceleration for rounded speed values, causing negative duration. Also assert more time values for easier debugging. See pybricks/support#786

For short maneuvers, t1 can be 0. If time is also 0, it wouldn't get into the first segment of the trajectory. See pybricks/support#786

While sub-degree maneuvers cannot be entered by users, we can still have sub-degree maneuvers if a new command is started while the trajectory is already near the target. This happens relatively often when restarting run_target towards the same target in a tight loop. See pybricks/support#786

If t1=0, the speed skips to w1 right away. Even though w0 is not used in that case, it still makes sense to give it a well defined value. This simplifies debugging and is useful for validation in tests. See pybricks/support#786

laurensvalk · 2022-11-11T14:04:33Z

@dlech Is it better with e.g. pybricks/pybricks-micropython@9af922d?

(Ignore the shaking, that's just excessive PID as mentioned above, but it may help make the actual bug occur more often.)

dlech · 2022-11-11T16:31:40Z

I can no longer reproduce the problem, so seems to be fixed, thanks!

dlech added bug Something isn't working topic: motors Issues involving motors software: pybricks-micropython Issues with Pybricks MicroPython firmware (or EV3 runtime) labels Nov 10, 2022

laurensvalk self-assigned this Nov 10, 2022

laurensvalk added a commit to pybricks/pybricks-micropython that referenced this issue Nov 11, 2022

pbio/trajectory: Fix evaluation at t=0 if t1=0.

a0a7760

For short maneuvers, t1 can be 0. If time is also 0, it wouldn't get into the first segment of the trajectory. See pybricks/support#786

dlech closed this as completed Nov 11, 2022

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Motor.run_target() raises RuntimeError #786

Motor.run_target() raises RuntimeError #786

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Motor.run_target() raises RuntimeError #786

Motor.run_target() raises RuntimeError #786

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