Inconsistent servo position, python, winch servo

Lynxmotion Electronics & Software
1

Hi,

I have been referencing the “Python/SSC-32 Example” thread and “SSC-32 Manual” for controlling the HS-785HB Winch Servo with Python v 2.6, OS X 10.6, with the SSC-32 motor controller. This is my first experience with both the SSC-32 and the winch servo. The problem is that I am unable to get the servo to go to a consistent position. The code below results in the winch servo moving in the same direction over and over, and not settling on a consistent position. Is this normal? What can I do to send the servo to some consistent location, for example, the center? Thank you in advance.

import serial

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

result = ssc32.write("# 0 P 1500 \r")
result = ssc32.write("# 0 P 1500 \r")
result = ssc32.write("# 0 P 1500 \r")

ssc32.close()

A few other notes about my system setup:

  • The board has jumpers exactly as shown here:
    lynxmotion.com/images/assemb … c32m01.gif
  • I’m on a MacBook Pro, 32 bit, OS X 10.6, Python 2.6 (but using pyserial2.5)
  • 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
2

The description of the problem hints that the servo controller is resetting probably due to not enough current to power the servo and the SSC-32. What sort of power supply are you using? Can you post an image of your wiring?

3

Hi, Thanks for that suggestion! It appears that the problem is solved. I now have a 9V battery at VL. A 6V power adapter (800 mA) at VS1, and I’ve removed the jumper at VL=VS1 and the two jumpers at VS2=VS1.

4

Good to know. If you still have issues you may want to get a 6vdc wall pack with more current. We have them at 2 amps and 3.3 amps. 800mA isn’t much to power servos. :wink: