AX-12a not responding to sync_write command

[wolf]

Hello,

I'm trying to implement a function to use the sync_write feature of the servos (in Python using PySerial), basically extending the lib_robotis.py library that was posted here recently from hizook.com.
I've added this to the USB2Dynamixel class, but when I execute the method, nothing happens. I was wondering if anyone might have any idea what's going on here:

Code: Select all

    def sync_send_write_instruction(self, servos, angs, angvels):
        ''' move servos to angles (radians)
        '''
        # verify validity of input commands
        for i in range(len(servos)):
            if angvels[i] > servos[i].settings['max_speed']:
                print 'lib_robotis.move_angle: angvel too high - %.2f deg/s' % (math.degrees(angvel))
                print 'lib_robotis.ignoring move command.'
                return
            if angs[i] > servos[i].settings['max_ang'] or angs[i] < servos[i].settings['min_ang']:
                print 'lib_robotis.move_angle: angle out of range- ', math.degrees(angs[i])
                print 'lib_robotis.ignoring move command.'
                return

        msg = [ 0XFF, 0XFF, 0XFE, (4+1) * len(servos) + 4, 0x83, 0X1E, 0X04 ] # header for sync_write message

        for i in range(len(servos)):
            enc_tics = int(round( angs[i] / servos[i].settings['rad_per_enc'] ))
            enc_tics += servos[i].settings['home_encoder']
            enc_tics = min( max( enc_tics, 0 ), servos[i].settings['max_encoder'] )
            hibyte_ang,lowbyte_ang = enc_tics / 256, enc_tics % 256 # hibyte, lowbyte for angle specification

            rpm = angvels[i] / (2 * math.pi) * 60.0
            angvel_enc = int(round( rpm / (114.0 / 1024.0) ))
            if angvel_enc<0:
                hibyte_vel,lowbyte_vel = abs(angvel_enc) / 256 + 4, abs(angvel_enc) % 256
            else:
                hibyte_vel,lowbyte_vel = angvel_enc / 256, angvel_enc % 256

            msg = msg + [ servos[i].servo_id,lowbyte_ang,hibyte_ang,lowbyte_vel,hibyte_vel ]

        chksum = self.calc_checksum( msg )
        msg = msg + [chksum] # add appropriate checksum value

        out = ''
        for m in msg:
            out += chr(m)
       
        print msg

        self.acq_mutex()
        try:
            self.send_serial( out )
        except:
            self.rel_mutex()
            raise
        self.rel_mutex()

thanks in advance!

[wolf]

i had the 0xFF 0xFF header included in the checksum calculation, one i removed that it worked!