#----------------------------------------------------------------------------
# Copyright (c) FIRST 2008-2012. All Rights Reserved.
# Open Source Software - may be modified and shared by FRC teams. The code
# must be accompanied by the FIRST BSD license file in the root directory of
# the project.
#----------------------------------------------------------------------------
import hal
from .analoginput import AnalogInput
from .interfaces import PIDSource
from .livewindow import LiveWindow
from .sensorbase import SensorBase
from .timer import Timer
__all__ = ["Gyro"]
[docs]class Gyro(SensorBase):
"""Interface to a gyro device via an :class:`.AnalogInput`
Use a rate gyro to return the robots heading relative to a starting
position. The Gyro class tracks the robots heading based on the starting
position. As the robot rotates the new heading is computed by integrating
the rate of rotation returned by the sensor. When the class is
instantiated, it does a short calibration routine where it samples the
gyro while at rest to determine the default offset. This is subtracted
from each sample to determine the heading.
.. not_implemented: initGyro
"""
kOversampleBits = 10
kAverageBits = 0
kSamplesPerSecond = 50.0
kCalibrationSampleTime = 5.0
kDefaultVoltsPerDegreePerSecond = 0.007
def __init__(self, channel):
"""Gyro constructor.
Also initializes the gyro. Calibrate the gyro by running for a number
of samples and computing the center value. Then use the
center value as the Accumulator center value for subsequent
measurements. It's important to make sure that the robot is not
moving while the centering calculations are in progress, this is
typically done when the robot is first turned on while it's sitting
at rest before the competition starts.
:param channel: The analog channel index or AnalogInput object that
the gyro is connected to. Gyros can only be used on on-board channels 0-1.
"""
if not hasattr(channel, "initAccumulator"):
channel = AnalogInput(channel)
self.analog = channel
self.voltsPerDegreePerSecond = Gyro.kDefaultVoltsPerDegreePerSecond
self.analog.setAverageBits(Gyro.kAverageBits)
self.analog.setOversampleBits(Gyro.kOversampleBits)
sampleRate = Gyro.kSamplesPerSecond \
* (1 << (Gyro.kAverageBits + Gyro.kOversampleBits))
AnalogInput.setGlobalSampleRate(sampleRate)
Timer.delay(1.0)
self.analog.initAccumulator()
self.analog.resetAccumulator()
# Only do this on a real robot
if not hal.HALIsSimulation():
Timer.delay(Gyro.kCalibrationSampleTime)
value, count = self.analog.getAccumulatorOutput()
self.center = int(float(value) / float(count) + .5)
self.offset = (float(value) / float(count)) - self.center
self.analog.setAccumulatorCenter(self.center)
self.analog.resetAccumulator()
self.setDeadband(0.0)
self.pidSource = PIDSource.PIDSourceParameter.kAngle
hal.HALReport(hal.HALUsageReporting.kResourceType_Gyro,
self.analog.getChannel())
LiveWindow.addSensorChannel("Gyro", self.analog.getChannel(), self)
[docs] def reset(self):
"""Reset the gyro. Resets the gyro to a heading of zero. This can be
used if there is significant drift in the gyro and it needs to be
recalibrated after it has been running.
"""
if self.analog is None:
return
self.analog.resetAccumulator()
[docs] def free(self):
"""Delete (free) the accumulator and the analog components used for the
gyro.
"""
if self.analog is not None:
self.analog.free()
self.analog = None
[docs] def getAngle(self):
"""Return the actual angle in degrees that the robot is currently
facing.
The angle is based on the current accumulator value corrected by the
oversampling rate, the gyro type and the A/D calibration values. The
angle is continuous, that is it will continue from 360 to 361 degrees. This allows
algorithms that wouldn't want to see a discontinuity in the gyro output
as it sweeps past from 360 to 0 on the second time around.
:returns: The current heading of the robot in degrees. This heading is
based on integration of the returned rate from the gyro.
:rtype: float
"""
if self.analog is None:
return 0.0
value, count = self.analog.getAccumulatorOutput()
value -= count * self.offset
return (value
* 1e-9
* self.analog.getLSBWeight()
* (1 << self.analog.getAverageBits())
/ (AnalogInput.getGlobalSampleRate() * self.voltsPerDegreePerSecond))
[docs] def getRate(self):
"""Return the rate of rotation of the gyro
The rate is based on the most recent reading of the gyro analog value
:returns: the current rate in degrees per second
:rtype: float
"""
if self.analog is None:
return 0.0
else:
return ((self.analog.getAverageValue() - (self.center + self.offset))
* 1e-9
* self.analog.getLSBWeight()
/ ((1 << self.analog.getOversampleBits()) * self.voltsPerDegreePerSecond))
[docs] def setSensitivity(self, voltsPerDegreePerSecond):
"""Set the gyro sensitivity. This takes the number of
volts/degree/second sensitivity of the gyro and uses it in subsequent
calculations to allow the code to work with multiple gyros. This value
is typically found in the gyro datasheet.
:param voltsPerDegreePerSecond:
The sensitivity in Volts/degree/second
:type voltsPerDegreePerSecond: float
"""
self.voltsPerDegreePerSecond = voltsPerDegreePerSecond
[docs] def setDeadband(self, volts):
"""Set the size of the neutral zone. Any voltage from the gyro less
than this amount from the center is considered stationary. Setting a
deadband will decrease the amount of drift when the gyro isn't
rotating, but will make it less accurate.
:param volts: The size of the deadband in volts
:type volts: float
"""
if self.analog is None:
return
deadband = int(volts * 1e9 / self.analog.getLSBWeight() *
(1 << self.analog.getOversampleBits()))
self.analog.setAccumulatorDeadband(deadband)
[docs] def setPIDSourceParameter(self, pidSource):
"""Set which parameter of the gyro you are using as a process
control variable. The Gyro class supports the rate and angle
parameters.
:param pidSource: An enum to select the parameter.
:type pidSource: :class:`.PIDSource.PIDSourceParameter`
"""
if pidSource not in (PIDSource.PIDSourceParameter.kRate,
PIDSource.PIDSourceParameter.kAngle):
raise ValueError("Must be kRate or kAngle")
self.pidSource = pidSource
[docs] def pidGet(self):
"""Get the output of the gyro for use with PIDControllers
:returns: the current angle according to the gyro
:rtype: float
"""
if self.pidSource == PIDSource.PIDSourceParameter.kRate:
return self.getRate()
elif self.pidSource == PIDSource.PIDSourceParameter.kAngle:
return self.getAngle()
else:
return 0.0
# Live Window code, only does anything if live window is activated.
def getSmartDashboardType(self):
return "Gyro"
def updateTable(self):
table = self.getTable()
if table is not None:
table.putNumber("Value", self.getAngle())
def startLiveWindowMode(self):
pass
def stopLiveWindowMode(self):
pass