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A2 Motor Classes

https://python-ev3dev.readthedocs.io/en/ev3dev-stretch/motors.html#large-ev3-motor

Motor classes

Units

Most methods which run motors will accept a speed argument. While this can be provided as an integer which will be interpreted as a percentage of max speed, you can also specify an instance of any of the following classes, each of which represents a different unit system:

class ev3dev2.motor.SpeedValue: A base class for other unit types. Don’t use this directly; instead, see SpeedPercent, SpeedRPS, SpeedRPM, SpeedDPS, and SpeedDPM.

class ev3dev2.motor.SpeedPercent(percent, desc=None): Speed as a percentage of the motor’s maximum rated speed.

class ev3dev2.motor.SpeedNativeUnits(native_counts, desc=None): Speed in tacho counts per second.

class ev3dev2.motor.SpeedRPS(rotations_per_second, desc=None): Speed in rotations-per-second.

class ev3dev2.motor.SpeedRPM(rotations_per_minute, desc=None): Speed in rotations-per-minute.

class ev3dev2.motor.SpeedDPS(degrees_per_second, desc=None): Speed in degrees-per-second.

class ev3dev2.motor.SpeedDPM(degrees_per_minute, desc=None): Speed in degrees-per-minute.

Example:

from ev3dev2.motor import SpeedRPM

# later...

# rotates the motor at 200 RPM (rotations-per-minute) for five seconds.
my_motor.on_for_seconds(SpeedRPM(200), 5)

Common motors

Tacho Motor (`Motor`)

class ev3dev2.motor.Motor(address=None, name_pattern='*', name_exact=False, **kwargs)

Bases: ev3dev2.Device

The motor class provides a uniform interface for using motors with positional and directional feedback such as the EV3 and NXT motors. This feedback allows for precise control of the motors. This is the most common type of motor, so we just call it motor.

COMMAND_RUN_FOREVER = 'run-forever': Run the motor until another command is sent.

COMMAND_RUN_TO_ABS_POS = 'run-to-abs-pos': Run to an absolute position specified by position_sp and then stop using the action specified in stop_action.

COMMAND_RUN_TO_REL_POS = 'run-to-rel-pos': Run to a position relative to the current position value. The new position will be current position + position_sp. When the new position is reached, the motor will stop using the action specified by stop_action.

COMMAND_RUN_TIMED = 'run-timed': Run the motor for the amount of time specified in time_sp and then stop the motor using the action specified by stop_action.

COMMAND_RUN_DIRECT = 'run-direct': Run the motor at the duty cycle specified by duty_cycle_sp. Unlike other run commands, changing duty_cycle_sp while running will take effect immediately.

COMMAND_STOP = 'stop': Stop any of the run commands before they are complete using the action specified by stop_action.

COMMAND_RESET = 'reset': Reset all of the motor parameter attributes to their default value. This will also have the effect of stopping the motor.

ENCODER_POLARITY_NORMAL = 'normal': Sets the normal polarity of the rotary encoder.

ENCODER_POLARITY_INVERSED = 'inversed': Sets the inversed polarity of the rotary encoder.

POLARITY_NORMAL = 'normal': With normal polarity, a positive duty cycle will cause the motor to rotate clockwise.

POLARITY_INVERSED = 'inversed': With inversed polarity, a positive duty cycle will cause the motor to rotate counter-clockwise.

STATE_RUNNING = 'running': Power is being sent to the motor.

STATE_RAMPING = 'ramping': The motor is ramping up or down and has not yet reached a constant output level.

STATE_HOLDING = 'holding': The motor is not turning, but rather attempting to hold a fixed position.

STATE_OVERLOADED = 'overloaded': The motor is turning, but cannot reach its speed_sp.

STATE_STALLED = 'stalled': The motor is not turning when it should be.

STOP_ACTION_COAST = 'coast': Power will be removed from the motor and it will freely coast to a stop.

STOP_ACTION_BRAKE = 'brake': Power will be removed from the motor and a passive electrical load will be placed on the motor. This is usually done by shorting the motor terminals together. This load will absorb the energy from the rotation of the motors and cause the motor to stop more quickly than coasting.

STOP_ACTION_HOLD = 'hold': Does not remove power from the motor. Instead it actively try to hold the motor at the current position. If an external force tries to turn the motor, the motor will push back to maintain its position.

address: Returns the name of the port that this motor is connected to.

command: Sends a command to the motor controller. See commands for a list of possible values.

commands

Returns a list of commands that are supported by the motor controller. Possible values are run-forever, run-to-abs-pos, run-to-rel-pos, run-timed, run-direct, stop and reset. Not all commands may be supported.

run-forever will cause the motor to run until another command is sent.
run-to-abs-pos will run to an absolute position specified by position_sp and then stop using the action specified in stop_action.
run-to-rel-pos will run to a position relative to the current position value. The new position will be current position + position_sp. When the new position is reached, the motor will stop using the action specified by stop_action.
run-timed will run the motor for the amount of time specified in time_sp and then stop the motor using the action specified by stop_action.
run-direct will run the motor at the duty cycle specified by duty_cycle_sp. Unlike other run commands, changing duty_cycle_sp while running will take effect immediately.
stop will stop any of the run commands before they are complete using the action specified by stop_action.
reset will reset all of the motor parameter attributes to their default value. This will also have the effect of stopping the motor.

count_per_rot: Returns the number of tacho counts in one rotation of the motor. Tacho counts are used by the position and speed attributes, so you can use this value to convert rotations or degrees to tacho counts. (rotation motors only)

count_per_m: Returns the number of tacho counts in one meter of travel of the motor. Tacho counts are used by the position and speed attributes, so you can use this value to convert from distance to tacho counts. (linear motors only)

driver_name: Returns the name of the driver that provides this tacho motor device.

duty_cycle: Returns the current duty cycle of the motor. Units are percent. Values are -100 to 100.

duty_cycle_sp: Writing sets the duty cycle setpoint. Reading returns the current value. Units are in percent. Valid values are -100 to 100. A negative value causes the motor to rotate in reverse.

full_travel_count: Returns the number of tacho counts in the full travel of the motor. When combined with the count_per_m atribute, you can use this value to calculate the maximum travel distance of the motor. (linear motors only)

polarity: Sets the polarity of the motor. With normal polarity, a positive duty cycle will cause the motor to rotate clockwise. With inversed polarity, a positive duty cycle will cause the motor to rotate counter-clockwise. Valid values are normal and inversed.

position: Returns the current position of the motor in pulses of the rotary encoder. When the motor rotates clockwise, the position will increase. Likewise, rotating counter-clockwise causes the position to decrease. Writing will set the position to that value.

position_p: The proportional constant for the position PID.

position_i: The integral constant for the position PID.

position_d: The derivative constant for the position PID.

position_sp: Writing specifies the target position for the run-to-abs-pos and run-to-rel-pos commands. Reading returns the current value. Units are in tacho counts. You can use the value returned by count_per_rot to convert tacho counts to/from rotations or degrees.

max_speed: Returns the maximum value that is accepted by the speed_sp attribute. This may be slightly different than the maximum speed that a particular motor can reach - it’s the maximum theoretical speed.

speed: Returns the current motor speed in tacho counts per second. Note, this is not necessarily degrees (although it is for LEGO motors). Use the count_per_rot attribute to convert this value to RPM or deg/sec.

speed_sp: Writing sets the target speed in tacho counts per second used for all run-* commands except run-direct. Reading returns the current value. A negative value causes the motor to rotate in reverse with the exception of run-to-*-pos commands where the sign is ignored. Use the count_per_rot attribute to convert RPM or deg/sec to tacho counts per second. Use the count_per_m attribute to convert m/s to tacho counts per second.

ramp_up_sp: Writing sets the ramp up setpoint. Reading returns the current value. Units are in milliseconds and must be positive. When set to a non-zero value, the motor speed will increase from 0 to 100% of max_speed over the span of this setpoint. The actual ramp time is the ratio of the difference between the speed_sp and the current speed and max_speed multiplied by ramp_up_sp.

ramp_down_sp: Writing sets the ramp down setpoint. Reading returns the current value. Units are in milliseconds and must be positive. When set to a non-zero value, the motor speed will decrease from 0 to 100% of max_speed over the span of this setpoint. The actual ramp time is the ratio of the difference between the speed_sp and the current speed and max_speed multiplied by ramp_down_sp.

speed_p: The proportional constant for the speed regulation PID.

speed_i: The integral constant for the speed regulation PID.

speed_d: The derivative constant for the speed regulation PID.

state: Reading returns a list of state flags. Possible flags are running, ramping, holding, overloaded and stalled.

stop_action: Reading returns the current stop action. Writing sets the stop action. The value determines the motors behavior when command is set to stop. Also, it determines the motors behavior when a run command completes. See stop_actions for a list of possible values.

stop_actions: Returns a list of stop actions supported by the motor controller. Possible values are coast, brake and hold. coast means that power will be removed from the motor and it will freely coast to a stop. brake means that power will be removed from the motor and a passive electrical load will be placed on the motor. This is usually done by shorting the motor terminals together. This load will absorb the energy from the rotation of the motors and cause the motor to stop more quickly than coasting. hold does not remove power from the motor. Instead it actively tries to hold the motor at the current position. If an external force tries to turn the motor, the motor will ‘push back’ to maintain its position.

time_sp: Writing specifies the amount of time the motor will run when using the run-timed command. Reading returns the current value. Units are in milliseconds.

run_forever(**kwargs): Run the motor until another command is sent.

run_to_abs_pos(**kwargs): Run to an absolute position specified by position_sp and then stop using the action specified in stop_action.

run_to_rel_pos(**kwargs): Run to a position relative to the current position value. The new position will be current position + position_sp. When the new position is reached, the motor will stop using the action specified by stop_action.

run_timed(**kwargs): Run the motor for the amount of time specified in time_sp and then stop the motor using the action specified by stop_action.

run_direct(**kwargs): Run the motor at the duty cycle specified by duty_cycle_sp. Unlike other run commands, changing duty_cycle_sp while running will take effect immediately.

stop(**kwargs): Stop any of the run commands before they are complete using the action specified by stop_action.

reset(**kwargs): Reset all of the motor parameter attributes to their default value. This will also have the effect of stopping the motor.

is_running: Power is being sent to the motor.

is_ramping: The motor is ramping up or down and has not yet reached a constant output level.

is_holding: The motor is not turning, but rather attempting to hold a fixed position.

is_overloaded: The motor is turning, but cannot reach its speed_sp.

is_stalled: The motor is not turning when it should be.

wait(cond, timeout=None)

Blocks until cond(self.state) is True. The condition is checked when there is an I/O event related to the state attribute. Exits early when timeout (in milliseconds) is reached.

Returns True if the condition is met, and False if the timeout is reached.

wait_until_not_moving(timeout=None)

Blocks until running is not in self.state or stalled is in self.state. The condition is checked when there is an I/O event related to the state attribute. Exits early when timeout (in milliseconds) is reached.

Returns True if the condition is met, and False if the timeout is reached.

Example:

m.wait_until_not_moving()

wait_until(s, timeout=None)

Blocks until s is in self.state. The condition is checked when there is an I/O event related to the state attribute. Exits early when timeout (in milliseconds) is reached.

Returns True if the condition is met, and False if the timeout is reached.

Example:

m.wait_until('stalled')

wait_while(s, timeout=None)

Blocks until s is not in self.state. The condition is checked when there is an I/O event related to the state attribute. Exits early when timeout (in milliseconds) is reached.

Returns True if the condition is met, and False if the timeout is reached.

Example:

m.wait_while('running')

on_for_rotations(speed, rotations, brake=True, block=True)

Rotate the motor at speed for rotations