time.sleep when controlling servo over pyserial

Projects Programming
1

Hi!
So I connected a motor controller that takes PWM input to my arduino such that as far as the arduino is concerned it is controlling a servo (0 negative thrust, 90 stop, 180 positive thrust).

I'm controlling this over pyserial and before I can send any command to my "servo" I have to give it a time.sleep() command of at least 1 second. Why is this necessary and how can I get around it?

Thanks in advance!

Here is my code thus far:

#!/usr/bin/env python

################################################
# Module:   servo.py
# Created:  2 April 2008
# Author:   Brian D. Wendt
#   http://principialabs.com/
# Version:  0.3
# License:  GPLv3
#   http://www.fsf.org/licensing/
'''
Provides a serial connection abstraction layer
for use with Arduino "MultipleSerialServoControl" sketch.
'''
################################################

import serial

# Assign Arduino's serial port address
#   Windows example
#     usbport = 'COM3'
#   Linux example
#     usbport = '/dev/ttyUSB0'
#   MacOSX example
#     usbport = '/dev/tty.usbserial-FTALLOK2'
usbport = '/dev/tty.usbmodem1411' #usb from arduino
# Set up serial baud rate
ser = serial.Serial(usbport, 9600, timeout=0)

def move(servo, angle):
    '''Moves the specified servo to the supplied angle.

    Arguments:
        servo
          the servo number to command, an integer from 1-4
        angle
          the desired servo angle, an integer from 0 to 180

    (e.g.) >>> servo.move(2, 90)
           ... # "move servo #2 to 90 degrees"'''

    if (0 <= angle <= 180):
        ser.write(chr(255))
        ser.write(chr(servo))
        ser.write(chr(angle))
    else:
        print("Servo angle must be an integer between 0 and 180.\n")

I can tell the robot to move with code like this:

import servo
import time
time.sleep(1)
servo.move(1, 90)
2

Opening the serial port resets the Arduino. There are ways to prevent that, but it makes more sense to modify the python program to open the port once, and then send a series of commands in a loop.

3

This Python - Arduino demo illustrates what @PaulS has suggested.

...R