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127 lines
4.0 KiB
ReStructuredText
127 lines
4.0 KiB
ReStructuredText
More about Motors
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===========================================
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Motor Tips & Tricks
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^^^^^^^^^^^^^^^^^^^
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.. The difference between ``run_angle`` and ``run_target``
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.. -------------------------------------------------------
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.. *TODO*
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.. _stalled:
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Using stall detection
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---------------------
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.. todo::
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This section will be included in a future release.
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.. When a motor cannot move any further despite using the maximally allowed
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.. torque we say that the motor is stalled. Something could be blocking the
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.. motor, or the load is just too heavy. For example, if you manually hold
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.. the motor shaft still while the motor is busy executing a command, the
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.. motor will stall.
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.. What can I do with stall detection?
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.. +++++++++++++++++++++++++++++++++++
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.. Stall detection is useful to detect that a motor can't move any further.
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.. This can be used to detect an endpoint of a mechanism. For example, you
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.. can detect whether a robotic hand is fully closed, because the gripper
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.. motor simply can't go further. This way, you don't need a touch or light
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.. sensor to detect this.
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.. *TODO: How, what, why. Explain run_until_stalled. Rack & pinion example.*
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.. When is a motor stalled?
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.. ++++++++++++++++++++++++
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.. TODO
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.. _gears:
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Using gears
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-----------------
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.. todo::
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This section will be included in a future release.
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.. Many LEGO robots use mechanisms with gears to change the speed and torque
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.. output of a motor. Let's consider the following dial mechanism.
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.. *TODO: INSERT PICTURE OF MOTOR WITH 12z gear AND 36z gear.*
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.. This gear train slows down the dial on the output axle by a factor of 3.
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.. Therefore, if you want to rotate the dial by 90 degrees, the motor has to
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.. rotate by 270 degrees. To turn at 200 degrees per second, the motor has to
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.. turn at 600 degrees per second, and so on.
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.. To avoid using this factor 3 everywhere in your program, you can use the
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.. `gears` setting of the ``Motor`` object, as shown in this example::
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.. # This example uses the EV3 brick, but the same
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.. # technique applies to other programmable hubs.
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.. ev3 = EV3Brick()
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.. # Initialize the motor. See picture above.
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.. dial = Motor(Port.C, Direction.COUNTERCLOCKWISE, gears=[12, 36])
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.. # Turn the dial by 90-degrees
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.. dial.run_angle(500, 90)
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.. # Print the dial angle
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.. print(dial.angle())
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.. # Turn the dial back to the original position
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.. dial.run_target(500, 0)
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.. When you use any of the other methods, the same scaling is applied. For
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.. example, you can print the angle of the dial as shown above. This will print
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.. 90 (approximately), even though the motor has turned 270 degrees.
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.. Notice that there is no magic going on. It is just a convenient scaling
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.. function. This helps you organize your code. For example, if you change
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.. your mechanism to use different gears, you only have to change the first
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.. line of this example.
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.. _control:
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The Control Class
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^^^^^^^^^^^^^^^^^
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The ``Motor`` class uses PID control to accurately track your commanded target
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angles. Similarly, the ``DriveBase`` class uses two of such controllers:
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one to control the heading and one to control the traveled distance.
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You can change the control settings through the following attributes, which are
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instances of the ``Control`` class given below.:
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- ``Motor.control``
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- ``DriveBase.heading_control``
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- ``DriveBase.distance_control``
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You can only change the settings while the controller is stopped. For example,
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you can set the settings at the beginning of your program. Alternatively, first
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call ``stop()`` to make your ``Motor`` or ``DriveBase`` stop, and then change
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the settings.
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.. autoclass:: pybricks.builtins.Control
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:no-members:
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.. rubric:: Settings
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.. automethod:: pybricks.builtins.Control.limits
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.. automethod:: pybricks.builtins.Control.pid
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.. automethod:: pybricks.builtins.Control.target_tolerances
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.. automethod:: pybricks.builtins.Control.stall_tolerances
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.. rubric:: Status
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.. automethod:: pybricks.builtins.Control.done
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