A quick demo of doing face tracking on the MeArm Pi so that you can make the arm follow you

face.py

from picamera.array import PiRGBArray
from picamera import PiCamera
import time
import cv2
from mearm import MeArm

width = 640

arm = MeArm()
arm.base.moveTo(0)

def detect(img, cascade):
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    rects = cascade.detectMultiScale(gray, scaleFactor=1.2, minNeighbors=4, minSize=(30, 30),
                                     flags=cv2.CASCADE_SCALE_IMAGE)
    if len(rects) == 0:
        return []
    rects[:,2:] += rects[:,:2]
    return rects

def draw_rects(img, rects, color):
    for x1, y1, x2, y2 in rects:
        cv2.rectangle(img, (x1, y1), (x2, y2), color, 2)

def find_centre(rects):
    max_rect = [999999, 999999, -1, -1]
    for x1, y1, x2, y2 in rects:
      if x1 < max_rect[0]: max_rect[0] = x1
      if y1 < max_rect[1]: max_rect[1] = y1
      if x2 > max_rect[2]: max_rect[2] = x2
      if y2 > max_rect[3]: max_rect[3] = y2
    centre = (max_rect[0] + (max_rect[2] - max_rect[0])/2, max_rect[1] + (max_rect[3] - max_rect[1])/2)
    return centre

# initialize the camera and grab a reference to the raw camera capture
camera = PiCamera()
camera.resolution = (width, int(width * 0.75))

faceCascade = cv2.CascadeClassifier('/usr/local/share/OpenCV/haarcascades/haarcascade_frontalface_default.xml')

cv2.startWindowThread()
cv2.namedWindow("viewer")
cv2.moveWindow("viewer", 0, 0)

while True:
    rawCapture = PiRGBArray(camera)
    # grab an image from the camera
    camera.capture(rawCapture, format="bgr")
    image = rawCapture.array
    rects = detect(image, faceCascade)

    print "Found {0} faces!".format(len(rects))
    if len(rects) > 0:
        draw_rects(image, rects, (255,0,0))

        centre = find_centre(rects)
        x_diff = centre[0] - (width/2)
        print x_diff
        angle = (x_diff / (float(width)/2)) * 27
        print angle
        arm.base.moveBy(-angle)
        cv2.circle(image, centre, 10, (255, 0, 0), 1)

    # display the image on screen
    cv2.imshow("viewer", image)

mearm.py

import os
import math
import pigpio
#import RPi.GPIO as GPIO

pi = pigpio.pi()

class Servo:
  def __init__(self, config):
    self.pin = config['pin']
    self.min = config['min']
    self.max = config['max']
    self.minAngle = config['minAngle']
    self.maxAngle = config['maxAngle']

  def moveTo(self, angle):
    self.moveToAngle(angle)

  def moveBy(self, angle):
    newAngle = self.currentAngle + angle
    self.moveToAngle(newAngle)

  def moveToCentre(self):
    centre = self.minAngle + (self.maxAngle - self.minAngle)/2
    self.moveToAngle(centre)

  def moveToAngle(self, angle):
    if angle > self.maxAngle:
      angle = self.maxAngle
    if angle < self.minAngle:
      angle = self.minAngle
    self.currentAngle = angle
    print("Moving servo %d to %d degrees" % (self.pin, angle))
    self.updateServo()

  def updateServo(self):
    pulseWidth = math.floor(self.min + ((float(self.currentAngle - self.minAngle) / float(self.maxAngle - self.minAngle)) * (self.max - self.min)));
    pi.set_servo_pulsewidth(self.pin, pulseWidth)

class MeArm:
  def __init__(self):
    self.base =  Servo({'pin': 4, 'min': 530, 'max': 2400, 'minAngle': -90, 'maxAngle': 90});
    self.lower = Servo({'pin': 17, 'min': 530, 'max': 1450, 'minAngle': 0, 'maxAngle': 90});
    self.upper = Servo({'pin': 22, 'min': 530, 'max': 2000, 'minAngle': 0, 'maxAngle': 135});
    self.grip =  Servo({'pin': 10, 'min': 1400, 'max': 2400, 'minAngle': 0, 'maxAngle': 90});