Python and SSC-32, consistent motion

Lynxmotion Electronics & Software
1

Hi, I have followed the “Python/SSC-32 Example” thread to write a short test program to control my servo (HS-785HB Winch Servo) with the SSC-32 motor controller and python (Macbook Pro OS X 10.6, Python 2.6, PySerial 2.5). I am using a Dynex USB to Serial Adapter Cable, connecting the SSC-32 to my usb port and a PL2303 driver for OS X 10.6.

import serial
SSC32_Port = "/dev/tty.usbserial";
ssc32 = serial.Serial(SSC32_Port, 115200);

result = ssc32.write("# 0 P 1500 \r") # P: 500-2500, 1500 is center
print result
result = ssc32.write("# 0 P 1200 \r") # P: 500-2500, 1500 is center
print result
result = ssc32.write("# 0 P 1800\r") # P: 500-2500, 1500 is center
print result

ssc32.close();

When I type each command into the terminal individually, I am able to get the expected behavior. However, when I run the entire program, the servo does not move. The terminal executes the three print statements, and then the program crashes my computer, presumably before it has a chance to close the serial port. Does anyone know what might be happening and what I can do to get consistent motion/behavior programmatically?

Thanks in advance!

2

Just a quick thought. You might want to add /n (line feeds) to your commands.

Alan KM6VV

3

Thanks for the tip KM6VV. What is the “\n” for in this case? I’ve added it, but it doesn’t seem to change the behavior.

4

I’ve noticed that adding time.sleep(5) statements helps to run and execute all the commands:

import serial
import time

SSC32_Port = "/dev/tty.usbserial";
ssc32 = serial.Serial(SSC32_Port, 115200);

result = ssc32.write("# 0 P 1500 \r\n") # P: 500-2500, 1500 is center
print result
time.sleep(5)
result = ssc32.write("# 0 P 1200 \r\n") # P: 500-2500, 1500 is center
print result
time.sleep(5)
result = ssc32.write("# 0 P 2000 \r\n") # P: 500-2500, 1500 is center
print result
time.sleep(5)

ssc32.close();

Perhaps there is a more elegant way to know when the servo is done with it’s motion?

5

Terminals often send CRLF, and I saw that you were only sending \r in your program. I can never remember which one the SSC-32 wants, so it was just a quick shot. (Carriage Return, Line Feed).

Alan KM6VV