Small Line Follower with Prime Hub and mixed Powered Up elements #149

JorgePe · 2020-10-13T21:29:47Z

JorgePe
Oct 13, 2020

Description

Just what the title says: a very small line follower with very few pieces to demonstrate Pybricks' potential
I flashed my Prime Hub from the 51515 Robot Inventor set with v3.0.0a9 so it now does dual boot and I can use pybricksdev with it through the USB cable.

Since I didn't want to disassemble my current 'Blast' configuration, I used just the hub with a few other pieces I had available - particularly 2 large Technic motors (identical to the large motors from the SPIKE set) and 1 Color/Distance sensor from the BOOST set.

Source Code

Code is very simple and quick tuned for running over a common sheet of paper. At this early stage of pybricks support for the Prime Hub, I have to run the code in tethered mode so a small closed circuit is enough for demonstration with a short USB cable connected to my laptop.

from pybricks.hubs import PrimeHub
from pybricks.parameters import Port, Color
from pybricks.pupdevices import Motor, ColorDistanceSensor
from pybricks.tools import wait

hub = PrimeHub()
mL = Motor(Port.E)
mR = Motor(Port.F)
s = ColorDistanceSensor(Port.A)

SPEED = 40    # duty cycle applied to motors (percentage)
TIME = 2         # time executing each step
THRESHOLD = 50    # threshold value for detecting the line
LIMIT = 5   # number of times a deviation is allowed before stepping a bit back

count = 0   

while True:
   # move forward
    mL.dc(-SPEED)
    mR.dc(SPEED)
    wait(TIME)
    v = s.reflection()
    print(v)
    if v < THRESHOLD :
        # move left
        mL.dc(SPEED)
        mR.dc(SPEED)
        count = 0
    else :
        if count < LIMIT :
            # move right
            mL.dc(-SPEED)
            mR.dc(-SPEED)
            count = count +1
        else:
            # move back to prevent deviation
            mL.dc(SPEED)
            mR.dc(-SPEED)
            wait(3*TIME)
            count = 0
    wait(2*TIME)

Building instructions
I believe there is no need for instructions as anyone can build this toy in less than 5 minutes

laurensvalk · 2020-10-14T07:15:19Z

laurensvalk
Oct 14, 2020
Maintainer

Thanks for sharing. I think you are the first user in the world to dual boot the Inventor Hub!

It's cool to see that these motors are already working as well - I don't have them.

If you like, here are some ideas for further exploration:

If you do mL = Motor(Port.E, Direction.COUNTERCLOCKWISE), positive speeds/duty will make it go forward too, making the rest of the script easier to interpret
You could try mR.dc(SPEED + steering) and mL.dc(SPEED - steering) with steering = (v - THRESHOLD)*KP

Disconnecting USB used to work, I think. We'll have to try that again. We might even change the way USB works after we enable Bluetooth. At that point, it could work just the like other hubs, leaving the USB free for other things like fast file transfer. We're not sure yet, so feel free to share your wishes and feature requests :)

0 replies

JorgePe · 2020-10-14T07:59:43Z

JorgePe
Oct 14, 2020
Author

Well you already said BT - using the Chrome IDE would be good for beginners since using text editor and pybricksdev might scare them. For me BT would also have the advantage of using the Nordic UART (if supported on this firmware) to cooperate with other systems until full messaging is available.

Can't remember any particular feature I might need... I am still trying to figure how to use most of the API like Grid and Speaker (I think still missing?). Generally speaking, having support for all internal devices of the PU family hubs would be great but it's already on the roadmap.

Thanks for the tips, will try them.

0 replies

laurensvalk · 2020-10-14T08:03:37Z

laurensvalk
Oct 14, 2020
Maintainer

Speaker is not implemented yet, but we're investigating to include (very basic) speech synthesis 🤓 .

There is some experimental IMU functionality in there already, so have a look at the experimental module, but we're going to have to rewrite it entirely to make it non-blocking before we will officially support it.

0 replies

JorgePe · 2020-10-14T08:08:37Z

JorgePe
Oct 14, 2020
Author

I already found the experimental IMU, had been using it with Control+ hub for a wristband-based HID controller - sending the output of the IMU to a "master" device on a bakcpack where it calculates the orientation of the wrist. But my math is very rust and only implemented 2 DOF.

0 replies

TechnicBRICKs · 2020-10-14T10:53:17Z

TechnicBRICKs
Oct 14, 2020

Have also tried to install the Pybricks firmware too, but regardless of not so smooth feedback progress at the console and the success message in the end, it always end booting with the LEGO firmware.

0 replies

laurensvalk · 2020-10-14T10:59:37Z

laurensvalk
Oct 14, 2020
Maintainer

That's a good sign! It means the update was successful.

This feature is not ready for average user yet, though. It's more like a proof of concept for now :)

Please use the Technic Hub for real projects for now. Switching over will be easy later since motors and sensors work the same across all hubs.

0 replies

TechnicBRICKs · 2020-10-14T11:13:08Z

TechnicBRICKs
Oct 14, 2020

Yeah! Not a real project, just wanted to give it a try! :)

0 replies

laurensvalk · 2020-10-14T11:17:48Z

laurensvalk
Oct 14, 2020
Maintainer

It's great to have your feedback, we appreciate it. This gives us more confidence in the procedure. It works just like the official update procedure, but still :) There's already a version on the way which will show progress using the pixels on the screen. When you reach 100%, all lights will be on.

As you have found, turning on the Pybricks firmware still need some work. The reason is this: by the time we check the button state, the power is not on yet, so it cannot read the button state.

0 replies

JorgePe · 2020-10-19T09:06:27Z

JorgePe
Oct 19, 2020
Author

Small update: thanks to a Laurens suggestion the robot no longer needs to be tethered so I can now let it run full speed on the floor.
I made some minor adjustments to the code so it now uses proportional control (and the code is also much simpler)

# with Laurens Valk tips
# for Proportional control and COUNTERCLOCKWISE option

from pybricks.hubs import PrimeHub
from pybricks.parameters import Port, Color, Direction, Button
from pybricks.pupdevices import Motor, ColorDistanceSensor
from pybricks.tools import wait

hub = PrimeHub()
mL = Motor(Port.E, Direction.COUNTERCLOCKWISE)
mR = Motor(Port.F)
s = ColorDistanceSensor(Port.A)

SPEED = 95
TIME = 1
THRESHOLD = 55
KP = 2.5

# wait for LEFT button to be pressed
while True:
    if hub.buttons.pressed() == [Button.LEFT] :
        break
    wait(10)

while True:
    wait(TIME)
    v = s.reflection()
    print(v)
    steering = (v - THRESHOLD) * KP
    mR.dc(SPEED + steering)
    mL.dc(SPEED - steering)

not sure about that "wait(TIME)" line... forgot to comment it but it probably works fine without it.
Had to adjust THRESHOLD a bit because the color/distance sensor was detecting the separation on my white floor tiles as lines and following them.

0 replies

laurensvalk · 2020-10-19T09:38:55Z

laurensvalk
Oct 19, 2020
Maintainer

Nice and clean 😄 Do you want to share the video link as well?

By the way, here's a another trick you can use to wait for any button:

# wait for any button to be pressed
while not any(hub.buttons.pressed()):
    wait(10)

0 replies

JorgePe · 2020-10-19T09:39:45Z

JorgePe
Oct 19, 2020
Author

I thought you would never ask :D

0 replies

TechnicBRICKs · 2020-10-19T10:23:14Z

TechnicBRICKs
Oct 19, 2020

Do you have new app script to flash the FW that supports unthetered operation? Best, Fernando Correia Sent without an iPhone... 😁

…

On Mon, Oct 19, 2020, 10:40 Jorge Pereira ***@***.***> wrote: I thought you would never ask :D https://youtu.be/oHwqm5GqPTU — You are receiving this because you commented. Reply to this email directly, view it on GitHub <https://github.com/pybricks/support/issues/149#issuecomment-711934076>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AQAYD3NVHHOT327U4JK4RYTSLQCPFANCNFSM4SPW6K3A> .

0 replies

JorgePe · 2020-10-19T10:42:06Z

JorgePe
Oct 19, 2020
Author

No, the firmware is the same.
I edited 2 lines in "connections.py" in the pybricksdev tool, it caused connection to keep stablished.
I can tell you the lines to comment but I think it is better if you wait for a new release of the pybricksdev tool, then you just update it fully with a single command

0 replies

JorgePe · 2020-10-19T10:47:59Z

JorgePe
Oct 19, 2020
Author

Since you are already using REPL, you can also copy&paste the whole script into it.

0 replies

laurensvalk · 2020-10-19T10:50:17Z

laurensvalk
Oct 19, 2020
Maintainer

I wonder, did USB still hang if you removed the print line from your loop?

0 replies

JorgePe · 2020-10-19T10:59:41Z

JorgePe
Oct 19, 2020
Author

yes it did.
The "pybricksdev run" command now ends and releases the connection:

Connecting to /dev/ttyACM0
2020-10-19 10:26:12,923:    INFO: Sending: 17%
2020-10-19 10:26:13,027:    INFO: Sending: 33%
2020-10-19 10:26:13,130:    INFO: Sending: 50%
2020-10-19 10:26:13,233:    INFO: Sending: 67%
2020-10-19 10:26:13,336:    INFO: Sending: 83%
2020-10-19 10:26:13,439:    INFO: Sending: 100%
2020-10-19 10:26:13,544:    INFO: Disconnected by client.

before the change, with our without the "print" command, i never saw that last line.

0 replies

JorgePe · 2020-10-19T11:01:01Z

JorgePe
Oct 19, 2020
Author

but before the change, I could re-run it again (as long as never removed the USB cable).
Now it gives me a checksum error, I need to first restart the hub.

0 replies

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Pybricks

Small Line Follower with Prime Hub and mixed Powered Up elements #149

JorgePe Oct 13, 2020

Replies: 17 comments

laurensvalk Oct 14, 2020 Maintainer

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