Added class MotorSet #336

dwalton76 · 2017-09-02T02:27:59Z

The MotorSet class can be used to start/stop more than one motor at once as close together as we possibly can. You can set different params for different motors in the set. Here is a small script I used to try a few things.

#!/usr/bin/env python3
from ev3dev.auto import OUTPUT_A, OUTPUT_B, OUTPUT_C, OUTPUT_D, Motor
from ev3dev.helper import LargeMotorPair
import argparse
import logging
import time
import sys

# logging
logging.basicConfig(level=logging.INFO,
                    format="%(asctime)s %(levelname)5s: %(message)s")
log = logging.getLogger(__name__)

log.info("start")
tank = LargeMotorPair(OUTPUT_A, OUTPUT_C)
tank.reset()
#tank.run_to_abs_pos(speed_sp=240, position_sp=360, stop_action='brake')
#tank.wait_until_not_moving()

motor_A = tank.motors[OUTPUT_A]
motor_C = tank.motors[OUTPUT_C]
tank.set_args(motors=[motor_A], speed_sp='120')
tank.set_args(motors=[motor_C], speed_sp='240')

tank.run_forever(stop_action='brake')
time.sleep(2)
tank.stop()
log.info("end")

dwalton76 · 2017-09-02T02:28:47Z

For issue #315

WasabiFan · 2017-09-02T02:39:00Z

ev3dev/helper.py

+    }
+    """
+
+    def __init__(self, motor_specs, desc=None):


Each motor object can tell you what port it's on... why does this need to take a dictionary?

The motor objects haven't been created yet though, we need to know what type of objects to make and which ports each of those objects is associated with.

Sorry, I read through the rest of the file then forgot to come back and delete this. I've got it now.

WasabiFan · 2017-09-02T02:42:58Z

ev3dev/helper.py

+                    log.info("%s: %s set %s to %s" % (self, motor, key, kwargs[key]))
+                    setattr(motor, key, kwargs[key])
+
+        for motor in motors:


I like this process (setting the properties then sending commands).

WasabiFan · 2017-09-02T02:45:38Z

ev3dev/helper.py

+            motor.wait_while(s, timeout)
+
+
+class LargeMotorPair(MotorSet):


I think we should figure out exactly what our goal is. In my mind, the most common scenario will be a pair of large motors which you want to "steer": even if internally we're using a generic MotorSet, I'd like to see if we can make the "pair" classes more specialized so they legitimately feel easy to use and work "out of the box".

yeah....to me part of it depends on what the user input is to control the steering. If it is the IR remote we have that implemented in the RemoteControlledTank class in helper.py...we could pull some of that code into a Mixin class that could be inherited here in LargeMotorPair. I also did a web interface for a tank, that could be pulled in too but loading the www modules makes the program take a while to load on an ev3. What other user input methods might we see for a MotorPair?

The scenarios I had in mind were:

"Run the left motor at 50% speed forward and the right motor at 10% speed backward"

"Run the two motors in a proportion of 3:1" (ratio, differential, etc.)

The second is a special case of the first. Note that the units are nonspecific and just an illustration. The idea is that this class is what's used whenever you have a driving robot... if you want to go straight, turn, spin, etc., you use this.

dwalton76 · 2017-09-02T02:53:06Z

ev3dev/helper.py

+        self.motors = OrderedDict()
+        for motor_port in sorted(motor_specs.keys()):
+            motor_class = motor_specs[motor_port]
+            self.motors[motor_port] = motor_class(motor_port)


The motor objects are created here

…thon into MotorPair

ddemidov · 2017-09-04T12:11:37Z

ev3dev/helper.py

+
+    def run_forever(self, **kwargs):
+        kwargs['command'] = ev3dev.auto.LargeMotor.COMMAND_RUN_FOREVER
+        self._run_command(**kwargs)


One thing I am not sure about is the logic of these run_* functions. Here you are pushing command into kwargs, and then filter it out in _run_command function. This cost a string comparison per key in kwargs, which could be negligible with respect to file acesses, but still is not free.

Why not create _set_args(self, **kwargs) function, and replace the two lines above with

self._set_args(**kwargs) self._run_command(ev3dev.auto.LargeMotor.COMMAND_RUN_FOREVER)

?

There is a set_args() (see line 187) and the user can do it this way if they want but they don't have to.

The price of the string compare feels worth it to me, it let me clean up this code a good bit by moving almost all of the logic to _run_command().

Well, I don't have strong feelings about this, so feel free to merge.

WasabiFan · 2017-09-04T18:26:15Z

ev3dev/helper.py

+        """
+
+        # Set the right_motor speed relative to the left_motor_speed
+        if set_right:


Huh, this isn't the behavior I had in mind 😆 I was thinking you would specify a speed and ratio, and it would run the fastest motor at that speed and the other one at a speed defined by the supplied ratio. My thinking was that we'd mimic the "steering" behavior of EV3-G.

Something like this?
https://github.com/ddemidov/ev3dev-lang-python/blob/master-deprecated/ev3dev/__init__.py#L85-L121

I haven't touched EV3-G since the day I found ev3dev :) Does its steering do what ddemidov points to or something else?

Looking at the "synchronized steer" code here, I think I can say that they don't match but @ddemidov's implementation would be preferred. LEGO seems to designate one motor as a "master", drive that one at the requested speed, and then run the other at a rate defined by the steering. I am no expert though so I may be mis-reading it.

WasabiFan · 2017-09-04T18:29:13Z

ev3dev/helper.py

+
+    def set_speed_percentage(self, left_motor_percentage, right_motor_percentage):
+        """
+        Set the speeds of the left_motor vs right_motor by percentage of their maximum speed


We should specify that the units are -100 to 100. The term "percentage" is often used to refer to [-1,1] or [0,1] by some programmers.

Ack...will also add some asserts to verify the inputs are within the range

WasabiFan · 2017-09-05T02:15:54Z

ev3dev/helper.py

+            *  0   means drive in a straight line, and
+            *  100 means turn right as fast as possible.
+
+        power: the power that should be applied to the outmost motor (the one


power? I think this should probably be "speed"

Caught that in the initial cut-n-paste....will change all of the power references to speed

WasabiFan · 2017-09-05T02:17:10Z

ev3dev/helper.py

+        log.debug("%s: direction %d, power %d, speed %d, left_power %d, right_power %d" %
+            (self, direction, power, speed, left_power, right_power))
+
+        self.left_motor.speed_sp = int(left_power)


We don't actually run a command here; is the expectation that you call set_speed_steering and then set the command in a loop? Note that updating the setpoint won't have an effect until a command is sent AFAIK.

yep it will be up to the user to call run_forever, run_timed, etc after this....all this function does is set them up with the desired speed_sp setting. Same goes for set_speed_percentage().

Hmm... In that case, we need to make sure we document the behavior!

WasabiFan

Looks good; we need to document the behavior of the new helper functions. I'm approving but I think we want to hold off on merging until we've finalized the v1.0.0 release.

dwalton76 · 2017-09-07T00:50:16Z

Is 1.0.0 out...shall we release the merging floodgates?

WasabiFan · 2017-09-07T00:56:10Z

Can you add a line to the documentation for set_speed_steering and the other related function explaining you need to call a run_* function afterward?

Also, is there anything we want to do here in response to #348 (e.g. renaming or changing the behavior to match EV3-G)?

dwalton76 · 2017-09-07T03:07:45Z

yep will add a line about needing to call run_XYZ

For #348 lets tackle any of that via a separate pull request. I need to take a look at what blocks EV3-G has, I'm not sure if the MotorSet class would cover one of them or not.

…thon into MotorPair

Added class MotorSet

7ca1471

dwalton76 requested review from WasabiFan and ddemidov September 2, 2017 02:29

WasabiFan reviewed Sep 2, 2017

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dwalton76 commented Sep 2, 2017

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Merge branch 'develop' of https://github.com/dwalton76/ev3dev-lang-py…

f928075

…thon into MotorPair

ddemidov reviewed Sep 4, 2017

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Added MotorPair set_speed_ratio() and set_speed_percentage()

99ec00b

ddemidov approved these changes Sep 4, 2017

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WasabiFan reviewed Sep 4, 2017

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WasabiFan mentioned this pull request Sep 5, 2017

Add v1.0.0 release to changelog #340

Closed

Changed set_speed_ratio to set_speed_steering

9fc40dc

WasabiFan reviewed Sep 5, 2017

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Change set_speed_steering power variable to speed

c87e182

dwalton76 mentioned this pull request Sep 5, 2017

support for holonomic robots #347

Open

WasabiFan approved these changes Sep 5, 2017

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dwalton76 added 2 commits September 7, 2017 03:14

Updated doc string for MotorPair set_ functions

ee8d22e

Merge branch 'develop' of https://github.com/dwalton76/ev3dev-lang-py…

e92130d

…thon into MotorPair

dwalton76 merged commit b93b22a into ev3dev:develop Sep 7, 2017

dwalton76 deleted the MotorPair branch September 7, 2017 03:19

Added class MotorSet #336

Added class MotorSet #336

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dwalton76 commented Sep 2, 2017

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dwalton76 commented Sep 7, 2017

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