Documentation

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:

R.motors[0].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. It will look something like this:

Found the following devices:
 - Motors:
    0: Motor( serialnum = "SR0XJ1F" )
    1: Motor( serialnum = "SR0A123" )

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”, you could do this instead:

R.motors["SR0A123"].something...

Setting motor power

Motor power is controlled using PWM with 100% power being a 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:

from sr.robot import *
import time

R = Robot()

# motor board 0, channel 0 to full power forward
R.motors[0].m0.power = 100

# motor board 1, channel 0 to full power reverse
R.motors[1].m0.power = -100

# motor board 0, channel 1 to half power forward
R.motors[0].m1.power = 50

# motor board 1, channel 0 stopped
R.motors[1].m0.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
time.sleep(2.5)       # wait for 2.5 seconds
R.motors[0].m1.power = 0

You can read the current power value for a motor using the same field:

# get the current output power of Motor Board 0, channel 0
currentTarget = R.motors[0].m0.power

Stopping the motors

When you set the motor power to 0, this signals the Motor Board to actively stop that motor from turning.

# store the motor in a local variable because typing it out gets really boring
molly = R.motors[0].m0

# set the power to 100 for a second, then stop immediately
molly.power = 100
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.

# set braking mode
molly.use_brake = False

# set the power to 100 for a second, then coast to a stop
molly.power = 100
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))

The use_brake value defaults to True and, just like the power value, will remain set until you change it.