Servo Blaster

Published on 2016-01-07 in Tote Zero.

So I have the robot assembled pretty much the way I wanted – the PCB as the body, a XM1584-based voltage regulator for steady 5V to the Pi and to servos, capacitor, power switch, 2S LiPo battery. Nothing fancy, really. I have no voltage monitoring this time, because the Pi doesn’t have an ADC that I could use (I might add one in the future versions), so I have to be careful about the battery use.

I also have the Servo Blaster , the daemon I’m using to generate PWM signal for the servos, all installed and configured, and I have a simple Python class to use it:

import math


class Servo(object):
    def __init__(self, servos, index, reverse=False, trim=0):
        self.servos = servos
        self.index = index
        self.reverse = reverse
        self.trim = trim

    def move(self, radians=None, degrees=None):
        self.servos.move(self.index, radians, degrees, self.reverse, self.trim)


class Servos(object):
    min_pos = 600
    max_pos = 2400
    unit = 4 # us
    max_servos = 12
    pos_range = 180

    def __init__(self):
        self.device = open('/dev/servoblaster', 'w')

    def __getitem__(self, index):
        return Servo(self, index)

    def move(self, servo, radians=None, degrees=None, reverse=False, trim=0):
        if degrees is None:
            degrees = math.degrees(radians)
        degrees += trim
        if reverse:
            degrees = self.pos_range - degrees
        position = self.min_pos + (degrees * self.pos_range /
                                   (self.max_pos - self.min_pos))
        position = min(self.max_pos, max(self.min_pos, position))
        output = position / self.unit
        self.device.write("{}={}\n".format(servo, output))

    def update(self):
        pass

Now it’s time for my favorite pastime (not): figuring out the order, orientation and trims for all the servos. Once I have that, I expect my code for the PyBoard to basically work – which means that I should have the basic creep gait. For now, I can move each of the servos individually, while the robot lies on its back, with a wifi dongle connected for control:

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