How to write to /dev/servoblaster from Python script?

Question

I'm working on a RPI controlled quadcopter. The PWM is generated by ServoBlaster. I've written a Python script to control the motors' speed. Assume that I'm using GPIO4 to control the motor. If I want to set the pulse wifth to 1000us I have to write this echo 0=1000us > /dev/servoblaster to the terminal (where 0 is the reference to the GPIO4). How can I run this command (writing 0=1000us to /dev/servoblaster) from a Python script in an effective way. The "effective" is important, because I've been using subprocess.call(["echo 0=1000us > /dev/servoblaster"], shell=True) , but this uses much CPU time.

I've also tried: python myScript > /dev/servoblaster, where myScript is:

print "0=1000us"

but it does nothing.

EDIT: I've tried this way:

dev = open('/dev/servoblaster', 'w')
dev.write('0=1000us\n')

but the servo does not moves.

Answer 1

Open /dev/servoblaster as you would any other file for writing.

Then write 0=1000us to the file.

You'll probably have to terminate every command with a new line, i.e write "0=1000us\n" to the file. If you don't terminate with a newline, the command won't be recognized as complete.

I'd keep the file open for the duration of your script rather than open, write, close for every change in pulse width.

• Alex: I've tried your solution but the servo does not moves
• joan: Check that the same command works from the command line. I've just checked with a simple Python script and it works for me (not with servoblaster, with /dev/pigpio).
• Alex: sorry but I don't understand what are you saying :(
• Alex: Yes, the servo works if I write this on the terminal: echo 0=1000us > /dev/servoblaster