High-level abstractions like Lejos

[pepijndevos]

If you have a look at the Lejos API, you'll see a bunch of lejos.hardware packages that provide very similar functionality to the ev3dev API. But there are also a lot of lejos.robotics packages that provide higher-level tools for common tasks such as localisation, mapping, and pathfinding, based on a common wheeled chassis interface.

I'm aware that this library has a MoveTank class that is similar to basic uses of lejos.robotics.chassis and maybe a subset of lejos.robotics.navigation.MovePilot, but there is a lot that has no equivalent.

Concretely, I was looking for an interface for a holonomic robot with omni-wheels. After fighting with Lejos a bit, I just wrote the following snippet

import numpy as np
angles = np.deg2rad([-36.8, -90, 36.8])
coef = np.array([np.sin(angles), np.cos(angles), [-1,1,1]]).T
speed = np.zeros(3)
# do stuff, set x, y, rotation speed
sp = coef.dot(speed)
# turn motors
motor_left.run_forever(speed_sp=sp[0])
motor_back.run_forever(speed_sp=sp[1])
motor_right.run_forever(speed_sp=sp[2])

I'm a functional guy, so I like the concept of just passing around a matrix to represent a wheeled platform. It generalizes nicely to any number of motors and supports generic math operations. You could have a MotorVector class that allows you to do speed_sp=[sp1, sp2, sp3] which would be sweet. But the rest of the library seems to be more OOP, and numpy is not a small dependency.

I'm curious what the best way would be to support more high-level interfaces in this library? The current structure of some utility classes scattered around the motor module seems not very suitable for a more complete robotics package. And if this package should be modeled on the Lejos API, the MoveTank, or something new, is up for debate. Or maybe these higher-level modules should even live in a different project.

[dwalton76]

It does seem that some of higher level classes in motor could also belong in their own files...wheeledbot.py or something like that? What do others think?

[dwalton76]

@pepijndevos you should grab #347

[WasabiFan]

I like the ideas here; we'd need to break it down into actionable features though (preferably in separate issues). The holonomic drive one is good.

[dwalton76]

We have a “control” directory which contains some code that kinda falls into this high level category.

Seems like first steps would be to move the following out of motor.py

• MoveTank
• MoveJoystick
• MoveDifferential (once it lands)

and into control/wheeledrobot.py? Not crazy about the filename since this code also works for tracked robots.

[dwalton76]

I am going to try to find some time to work on #235 that one also falls under this category

[WasabiFan]

I'm not super excited about moving things around (because it's a breaking change) but that may be warranted here. If we do so, I'd suggest calling it ev3dev2.drive.