Update the motor board docs for SR2022

Author: trickeydan

programming/sr/motors/index.md

@@ -6,72 +6,70 @@ title: Motors
 Motors
 ======
 
-The `motors` object is used to control a collection of Motor Boards.
-Similar to `ruggeduinos` and `servos`, `motors` can be used like a list.
-To do something with the **first Motor Board**, you would use:
+The `motor_board` object is used to control a collection of Motor Boards.
+
+When a single Motor Board is connected to your robot, you can control it
+using the `motor_board` object.
 
 ~~~~~ python
-R.motors[0].something...
+R.motor_board.something...
 ~~~~~
 
-...because indexes are 0-based (counting starts from 0, not 1).
-
-When you have more than one Motor Board connected to your kit they will be ordered based upon their SR Part Code, as written on the underside of the board.
-
-The SR Part Code of each detected Motor Board is also printed to the log when your robot starts.
+The serial number of each detected Motor Board is printed to the log when your robot starts.
 It will look something like this:
 
 ~~~~~ not-code
-Found the following devices:
- - Motors:
-    0: Motor( serialnum = "SR0XJ1F" )
-    1: Motor( serialnum = "SR0A123" )
+sr.robot3.robot INFO - Found Student Robotics Motor Board v4 - srABC1
 ~~~~~
 
-
-However, like `ruggeduinos` and `servos`, `motors` is actually a dictionary.
-As a result, in `motors` you can also use the SR Part Code of the Motor Board as a key.
-For example, if you had a board that was labelled "SR0A123",
+If you have more than one Motor Board attached, the `motor_boards` object can be used to control a collection of Motor Board. It is a dictionary access via serial number, which is usually written on the board. For example, if you had a board whose serial number was "srABC1",
 you could do this instead:
 
 ~~~~~ python
-R.motors["SR0A123"].something...
+R.motor_boards["srABC1"].something...
 ~~~~~
 
+<div class="warning">
+    When you have more than one Motor board connected to your kit,
+    you must use `R.motor_boards` and index by serial number. This is so
+    that the kit knows which Motor Board you want to control.
+</div>
+
+
 Setting motor power
 -------------------
 
 Motor power is controlled using [PWM](https://en.wikipedia.org/wiki/Pulse-width_modulation) with 100% power being a [duty cycle](https://en.wikipedia.org/wiki/Duty_cycle) of 1. You set the power with an integer value between -100 and 100 inclusive (where a negative value puts the motor in reverse). The field to change the output power is `power`. As each Motor Board has two outputs you will need to specify which output you want to control:
 
 ~~~~~ python
-from sr.robot import *
+from sr.robot3 import *
 import time
 
 R = Robot()
 
-# motor board 0, channel 0 to full power forward
-R.motors[0].m0.power = 100
+# motor board srABC1, channel 0 to full power forward
+R.motor_boards["srABC1"].motors[0].power = 1
 
-# motor board 1, channel 0 to full power reverse
-R.motors[1].m0.power = -100
+# motor board srXYZ1, channel 0 to full power reverse
+R.motor_boards["srXYZ1"].motors[0].power = -1
 
-# motor board 0, channel 1 to half power forward
-R.motors[0].m1.power = 50
+# motor board srABC1, channel 1 to half power forward
+R.motor_boards["srABC1"].motors[1].power = 0.5
 
-# motor board 1, channel 0 stopped
-R.motors[1].m0.power = 0
+# motor board srXYZ1, channel 0 stopped
+R.motor_boards["srXYZ1"].motors[0].power = 0
 
-# the following will put motor board 0, channel 1 at 25% power (forwards) for 2.5 seconds:
-R.motors[0].m1.power = 25
+# the following will put motor board srABC1, channel 1 at 25% power (forwards) for 2.5 seconds:
+R.motor_boards["srABC1"].motors[1].power = 0.25
 time.sleep(2.5)       # wait for 2.5 seconds
-R.motors[0].m1.power = 0
+R.motor_boards["srABC1"].motors[1].power = 0
 ~~~~~
 
 You can read the current power value for a motor using the same field:
 
 ~~~~~ python
-# get the current output power of Motor Board 0, channel 0
-currentTarget = R.motors[0].m0.power
+# get the current output power of Motor Board srABC1, channel 0
+currentTarget = R.motor_boards["srABC1"].motors[1].power
 ~~~~~
 
 Stopping the motors
@@ -81,29 +79,28 @@ When you set the motor power to 0, this signals the Motor Board to actively stop
 
 ~~~~~ python
 # store the motor in a local variable because typing it out gets really boring
-molly = R.motors[0].m0
+molly = R.motor_boards["srABC1"].motors[1]
 
-# set the power to 100 for a second, then stop immediately
-molly.power = 100
+# set the power to 100% for a second, then stop immediately
+molly.power = 1
 time.sleep(1)
 molly.power = 0
 ~~~~~
 
 However, you may also want to allow the motors to gently coast to a halt.
-This can be achieved by setting the `use_brake` field of the individual motor.
+This can be achieved by using the special `COAST` value.
 
 ~~~~~ python
-# set braking mode
-molly.use_brake = False
-
-# set the power to 100 for a second, then coast to a stop
-molly.power = 100
+# set the power to 100% for a second, then coast to a stop
+molly.power = 1
 time.sleep(1)
-molly.power = 0
-
-# Print the current braking mode (might be handy for debugging!)
-print("m0.use_brake = {0}".format(molly.use_brake))
+molly.power = COAST
 ~~~~~
 
-The `use_brake` value defaults to `True` and, just like the `power` value,
-will remain set until you change it.
+When the power of the motor is set to `0`, it is equivalent to setting
+the power to `BRAKE`.
+
+~~~~~ python
+# set the motor to brake
+molly.power = BRAKE
+~~~~~