Robot class for Walkers

[scotus-49]

Does Pybricks have a Robotics Class for walking robots?

I am prototyping a 6-leg simple walker built on the Movehub, using the two built-in motors to drive right and left leg systems independently. I can only find robotics information for wheeled robots in the Pybricks docs. Can this be adapted for walking Robots, with some way of synchronizing the initial motor setup?

Pybricks works great, and my prototype clambers around when I press run/send. I'd love to have a bit more variety than just going in a staight(ish) line though, but could use some help.

All hints would be very much appreciated.

[laurensvalk]

The plan is that several more generic classes will be added to the robotics module.

I can't see from the picture, but does the mechanism work by just running the motors constantly? If so, since your creation uses two motors, you might be able to just use the DriveBase. With clever choices of diameter and axle_track, you can essentialy scale what the motors will do when you use the straight and turn methods for given values.

These two methods will keep the motors in sync as well.

Does this mechanism provide a way of detecting the right initial configuration? If so, you can make your robot attain that pose before you initialize the DriveBase, simply using the invididual motor methods, one leg at a time.

[scotus-49]

@laurensvalk:
Thank you so much for your advice - helpful as always. Meanwhile my project has evolved a bit further, and now has the interactive motor turning the color/distance sensor (mounted on a vertical rotating axle at the front) to enable the robot to scan its immediate environment in a roughly 120 degree horizontal angle.

I've added a few deco elements to take away from the bare skeleton look, and have solved quite a few problems interfacing Lego Technic and the traditional stuff. But the Boost set contains quite a few useful in-between pieces.

I will definitely look into using the DriveBase. I also want to use the fact that the walk mechanism creates pitch and yaw on the MoveHub, and hope to use the built-in movement sensor to vary the leg mechanism motor speeds to give more torque when the higher (orange) centre leg is operational.

I have to say that the joy in pushing the start/load button and having one's own creation almost instantly moving and reacting to the software coding is quite something. Thanks again for Pybricks!

[scotus-49]

@laurensvalk:
I've had some partial success with using DriveBase, but not the movement I expected.

Using straight() turned my robot round in a circle, while turn() marched straight ahead. I swapped over the left and right motors, but the robot did not change direction - clockwise viewed from the top. I experimented with a few different values for the wheel_diameter, but nothing changed.

Here's my code:

from pybricks.hubs import MoveHub
from pybricks.pupdevices import Motor
from pybricks.parameters import Port, Stop
from pybricks.tools import wait
from pybricks.robotics import DriveBase

hub = MoveHub()

# built-in motors
motor_a = Motor(Port.A)
motor_b = Motor(Port.B)
# interactive motor
motor_c = Motor(Port.C)

print("Experimenting with DriveBase")

myDriveBase = DriveBase(motor_a, motor_b, 10, 100)

# goes forward
myDriveBase.turn(180)

# turns in a circle but not 90 deg.
myDriveBase.straight(90)

Have I done something wrong?

The turning movement (coded with straight) is just what I wanted, and the robot turned nicely around its centre. It was enjoyable to watch.

Francis Sim

[laurensvalk]

I think you’ll want to set the positive direction of one of the motors as counterclockwise (using the Direction.COUNTERCLOCKWISE when you initialize motor A or B, whichever fits your application best.)

[scotus-49]

@laurensvalk:
Thanks for the advice - it worked straight away!

I added motor_a = Motor(Port.A, Direction.COUNTERCLOCKWISE) and my robot marched forward, but only with a negative number in myDriveBase.straight(). A positive number worked as expected - reversing off of my worktop. Other directional combinations for my two motors produced only a turning movement.

The turn() now also works as expected. but I could not get drive() to do anything, possibly it's a coding mistake by me. I have successfully used duty cycle to rotate my front-mounted sensor alternatively left and right.

Now I can start to fine tune-my code. I'm new to multi-legged things, so this is both exploration and fun. Thanks again for Pybricks!

[laurensvalk]

I added motor_a = Motor(Port.A, Direction.COUNTERCLOCKWISE) and my robot marched forward, but only with a negative number in myDriveBase.straight()

In that case, try doing it for B, not A.

I could not get drive() to do anything

If turn and straight work, drive should work also. Keep in mind that drive just begins driving and does not wait until a particular target (a straight distance or a turn angle) is complete.

So if drive is the last thing in your program, your program ends and the motors stop. If this was the case, just add a wait with a desired duration of the motion.

[scotus-49]

Thanks for the information - I'll check this out.

Is it the case with the MoveHub that when I am running DriveBase the third (interactive) motor will not run at the same time? It seems I have an either/or situation with my robot - it's not a problem, just good to know for coding.

[laurensvalk]

They can be used at the same time. Depending on what you’d like to achieve, perhaps the ‘wait’ argument in some of the motor commands might help.

[scotus-49]

I still cannot get my MoveHub to recognise or do anything with drive() from Pybricks Robotics class.

Using a bare minimum build, running in front wheel drive mode:

and the following code:

from pybricks.hubs import MoveHub
from pybricks.pupdevices import Motor
from pybricks.parameters import Port, Stop, Direction
from pybricks.tools import wait
from pybricks.robotics import DriveBase

hub = MoveHub()

# built-in motors
motor_a = Motor(Port.A,  Direction.COUNTERCLOCKWISE)
motor_b = Motor(Port.B)

print("Using the DriveBase:")

myDriveBase = DriveBase(motor_a, motor_b, 29, 65)
myDriveBase.settings(80, 100, 50, 200)

# driving forward
myDriveBase.drive(150, 5)

dist = myDriveBase.distance()
print("Distance traveled is %s mm" %(dist))

The console printout reads Distance traveled is 0 mm which is quite correct in this case. The LED briefly flashed green, and quickly returned to blue.

For myDriveBase.straight(150) everything works nicely, and the programmed distance of 150 measured 150mm after moving. distance() gave me a readout of 151 in the forward direction and 150 in reverse. This is very impressive, since the Lego Boost set is essentially sold as a children's toy. Pybricks certainly has a lot under the bonnet!

Is it my coding that's preventing drive() from working, or is it something about the MoveHub, or maybe some bugs somewhere? Any help would be appreciated.

[laurensvalk]

This is what I described above. Your program ends almost instantly after you give the drive command, so there is no time to see any movement 😄

Try adding a few seconds waiting using:

wait(2000)

[scotus-49]

I've added the wait(2000) and the hub moved forward, but it stopped after about 2 seconds. As expected, a wait(5000) makes the hub run for approx. 5 seconds then stops. How do I code continuous movement?

[laurensvalk]

How do I code continuous movement?

As in, move forever?

Here is one way to wait until the end of times, or until the batteries run out, whichever comes first:

while True:
    wait(1000)
    # You can do other things in the loop too, like occasionally printing the distance value

[laurensvalk]

You can use the same technique to drive until the sensor detects something:

myDriveBase.drive(150, 5)
while my_sensor.distance() <= 50:
    wait(10)
myDriveBase.stop()
print("I drove for", myDriveBase.distance(), "mm")

This is essentially what drive is for. For straight or turn you need to know how far you want to move. With drive you just start moving and you can choose the right moment to stop, such as after detecting an obstacle in this example.

[scotus-49]

Thanks - I'd just worked it out myself, and then your reply came in . Sorry, I should have seen that.

Thanks again for your fantastic help!