I am currently working on a project the uses 2 servo motors for a pan and tilt camera system, while developing my code i noticed that the servos suffer from a jitter due to the OS interrupting th PWM signal to the servos. As a solution to this I decided to only move them in small increments by switching the servos on moving them and then off again using the .start(pos) and .stop() methods. I then noticed that after around 250 individual moves of the servos both will cease to move from that point on. the program does not crash and no warning or errors are thrown. after resetting the environment they will work again for another 250 moves. is there a limit to the amount of times a servo can have the .start() called on it?
i created my own modules for initializing a servo object which i will post below
As far as i can tell there is no issue with the standard generic servo motors which were purchased on eBay.
i have wrote a few simple test that use the servo module and freeze the servos after 250 moves.
using the repos method.
The objects coord value continues to be updated even though the servo does not move.
Code: Select all
## servo motor moduule
import RPi.GPIO as GPIO
from time import sleep
import sys
#GPIO.setwarnings(False)
class ServoMotor:
def __init__(self, pinNo, type):
self.pinNo = pinNo
self.type = type
GPIO.setmode(GPIO.BCM)
GPIO.setup(self.pinNo,GPIO.OUT)
self.pos = GPIO.PWM(self.pinNo,50)
self.coord = 7.5
self.pos.start(self.coord)
sleep(0.5)
self.pos.stop()
self.posMax = 0.0
self.posMin = 0.0
if(self.type == "H"):
self.posMax = 12.5
self.posMin = 2.8
else:
self.posMax = 11
self.posMin = 4
def repos(self, state):
changeUnit = 0.06
try:
GPIO.setmode(GPIO.BCM)
self.pos = GPIO.PWM(self.pinNo,50)
if(state == "pos"):
if(self.coord + changeUnit < self.posMax):
self.coord = self.coord + changeUnit
self.pos.start(self.coord)
sleep(0.1)
self.pos.stop()
else:
self.pos.start(self.posMax)
elif(state == "neg"):
if(self.coord - changeUnit > self.posMin):
self.coord = self.coord - changeUnit
self.pos.start(self.coord)
sleep(0.1)
self.pos.stop()
else:
self.pos.start(self.posMin)
else:
print("unknown state: " + str(state))
quit()
except Exception as e:
print("Error while repositioning in the servo module: " + str(e))
quit()
def reposition(self, position):
self.pos = GPIO.PWM(self.pinNo,50)
if(self.type == "H"):
if(position == "Front"):
self.coord = 7.5
self.pos.start(self.coord)
sleep(0.5)
#print("Front")
elif(position == "Left"):
self.coord = 12.5
self.pos.start(self.coord)
sleep(1)
#print("Left")
elif(position == "Right"):
self.coord = 2.8
self.pos.start(self.coord)
sleep(1)
#print("Right")
else:
try:
self.pos.start(position)
sleep(0.2)
except:
self.pos.stop()
else:
try:
self.pos.start(position)
sleep(0.2)
except:
print("ERROR: invalid position")
self.pos.stop()
def getInfo(self):
print("=========" + str(self.type) + "=========")
print("Current coords:" + str(self.coord))
print("max coord:" + str(self.posMax))
print("min coord:" + str(self.posMin))
print("pin no.:" + str(self.pinNo))
print("===================")
