brake_sine.py

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#!/usr/bin/env python

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# Copyright (c) 2018, Dataspeed Inc.
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import rospy
import math

from std_msgs.msg import Bool
from dbw_fca_msgs.msg import BrakeCmd


class SineTest:
    def __init__(self):
        rospy.init_node('sine_test')
        self.pub = rospy.Publisher('/vehicle/brake_cmd', BrakeCmd, queue_size=1)
        self.sub = rospy.Subscriber('/vehicle/dbw_enabled', Bool, self.recv_enable)

        self.high_peak = rospy.get_param('~high_peak', 0.40)
        self.low_peak = rospy.get_param('~low_peak', 0.15)
        self.period = rospy.get_param('~period', 10)

        self.enabled = False
        self.t = 0
        self.sample_time = 0.02

        rospy.Timer(rospy.Duration(self.sample_time), self.timer_cb)

    def timer_cb(self, event):
        if not self.enabled:
            self.t = 0
            return

        amplitude = 0.5 * (self.high_peak - self.low_peak)
        offset = 0.5 * (self.high_peak + self.low_peak)
        cmd = offset - amplitude * math.cos(2 * math.pi / self.period * self.t)
        self.t += self.sample_time

        self.pub.publish(BrakeCmd(enable=True, pedal_cmd_type=BrakeCmd.CMD_PEDAL, pedal_cmd=cmd))

    def recv_enable(self, msg):
        self.enabled = msg.data


if __name__ == '__main__':
    try:
        node_instance = SineTest()
        rospy.spin()
    except rospy.ROSInterruptException:
        pass