Raspberry Pi Forums

Neid wrote: ↑

Sat Apr 25, 2020 10:46 am

I'm trying to send commands from raspberry pi 3b+ to 32 CH servo control board with serial communication through USB.

Code: Select all

import serial
import time

ser = serial.Serial('/dev/ttyACM0', baudrate=115200,
                    parity=serial.PARITY_NONE,
                    stopbits=serial.STOPBITS_ONE,
                    bytesize=serial.EIGHTBITS
                    )
while True:
    ser.write(b"#3P1100T500D0\n")
    print("1100")
    time.sleep(0.5)
    ser.write(b"#3P1800T500D0\n")
    print("1800")
    time.sleep(0.5)
    

After first command (3P1100T500D0) is executed nothing happens and i have to unplug and plug in again board to even use first command in the code.

B.Goode wrote: ↑

Sat Apr 25, 2020 11:04 am

Neid wrote: ↑

Sat Apr 25, 2020 10:46 am

I'm trying to send commands from raspberry pi 3b+ to 32 CH servo control board with serial communication through USB.

Code: Select all

import serial
import time

ser = serial.Serial('/dev/ttyACM0', baudrate=115200,
                    parity=serial.PARITY_NONE,
                    stopbits=serial.STOPBITS_ONE,
                    bytesize=serial.EIGHTBITS
                    )
while True:
    ser.write(b"#3P1100T500D0\n")
    print("1100")
    time.sleep(0.5)
    ser.write(b"#3P1800T500D0\n")
    print("1800")
    time.sleep(0.5)
    

After first command (3P1100T500D0) is executed nothing happens and i have to unplug and plug in again board to even use first command in the code.

Raspberry Pi documentation for USB troubleshooting here - https://www.raspberrypi.org/documentati ... /README.md

And information about UART/serial comms here - https://www.raspberrypi.org/documentati ... on/uart.md


I wonder if you have correctly identified the serial device as ttyACM0?

Have you tried a simple loopback data test on the serial device prior to the complexity of attempting to communicate with the servo controller?

scruss wrote: ↑

Sat Apr 25, 2020 3:10 pm

There's this very old thread about SSC-32 control where it turns out that the board needs \r instead of \n to accept a command: Controlling SSC-32 servo controler board with RPi - Raspberry Pi Forums. Have you tried that?

Although you're writing, not reading, serial.Serial should set a timeout to allow commands to fail. Without it, your program may wait forever for serial commands to finish. Adding something like serial.Serial(… , timeout=1) at least should fail and tell you why.

If this is one of those Maestro/SSC-32 clones (a link to what you have would really help!), you seem to be sending it a move command, wait half a second, another move command, wait another half second, reissue the first move command … repeat forever. Can you query the board to see if the servos have moved (close) to the positions you asked them to before issuing another command? I haven't used this board, and servos are something I only use now and again, but it always surprises me how long it takes for a servo to move.

There may be a higher-level Python module for controlling your board: GitHub - FRC4564/Maestro: Python class to support Pololu's Maestro servo controller over USB serial. Great with Raspberry Pi. - but this may only work with boards that provide the two serial ports, and your screenshot only shows one, ttyACM0.

Neid wrote: ↑

Sat Apr 25, 2020 4:10 pm

Link to the board
https://pl.aliexpress.com/item/32272674 ... 5c0f7dISrt

hippy wrote: ↑

Sat Apr 25, 2020 5:00 pm

Neid wrote: ↑

Sat Apr 25, 2020 4:10 pm

Link to the board
https://pl.aliexpress.com/item/32272674 ... 5c0f7dISrt

Do you have a link to the datasheet for the board ?

/*
 * test.c:
 * Copyright (c) 2014-2020 Rtrobot. <admin@rtrobot.org>
 *  <http://rtrobot.org>
 ***********************************************************************
*  1.Inatall wiringPi at <http://wiringpi.com/>
*  2. Connect to board via usb
*  3.build:
*       gcc -o test test.c -lwiringPi
*  4.run to test:
*       ./test
 ***********************************************************************
 */


#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <wiringPi.h>
#include <wiringSerial.h>

void wait_serial_return_ok(int fd)
{
	int num=0;
	while(1)
    {
		char c[16];
		c[num]=serialGetchar(fd);
		if(c[num-1]=='O'&&c[num]=='K')
			break;
		num++;
		if(num>=15)
			num=0;
    }
}

int main(int argc, char *argv[])
{
	int fd;
	if ((fd = serialOpen("/dev/ttyACM0", 115200)) < 0)
    {
		fprintf(stderr, "Unable to open serial device: %s\n", strerror(errno));
		return 1 ;
    }

	serialPuts(fd, "#1P2000T1000D100\r\n");
	//Waiting to return OK
	wait_serial_return_ok(fd);
	serialPuts(fd, "#1P1000#2P666T1000D2333\r\n");
	wait_serial_return_ok(fd);
	
	//Test for send wrong instruction
	serialPuts(fd, "#3P2500T9000D9000\r\n");
		
	//Stop wrong instruction
	serialPuts(fd, "~ST");
		
	//Change right instruction
	serialPuts(fd, "#2P2500T9000D9000\r\n");
	wait_serial_return_ok(fd);
		
	//Test for action groups,Group 1 run 3 times
	serialPuts(fd, "G1F3\r\n");
	wait_serial_return_ok(fd);
	
	//Close serial
	serialClose(fd);
	return 0;
}

1. All commands end with "\r\n".
2. The test program waits for OK to be returned from the serial port

scruss wrote: ↑

Sat Apr 25, 2020 6:10 pm

Looking at the logo, it's from RTRobot.
Current Linux software - including manual and Raspberry Pi code - seems to live here: http://www.rtrobot.org/software/
You want Servo Controller X64 for Linux. It's a big/slow download, and there are some precompiled things in there that might not be the best things to run.

Slightly more easy to get manual: https://www.scribd.com/document/4421260 ... h-V2-6-pdf

There's a tiny C example for Raspberry Pi:

Code: Select all

/*
 * test.c:
 * Copyright (c) 2014-2020 Rtrobot. <admin@rtrobot.org>
 *  <http://rtrobot.org>
 ***********************************************************************
*  1.Inatall wiringPi at <http://wiringpi.com/>
*  2. Connect to board via usb
*  3.build:
*       gcc -o test test.c -lwiringPi
*  4.run to test:
*       ./test
 ***********************************************************************
 */


#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <wiringPi.h>
#include <wiringSerial.h>

void wait_serial_return_ok(int fd)
{
	int num=0;
	while(1)
    {
		char c[16];
		c[num]=serialGetchar(fd);
		if(c[num-1]=='O'&&c[num]=='K')
			break;
		num++;
		if(num>=15)
			num=0;
    }
}

int main(int argc, char *argv[])
{
	int fd;
	if ((fd = serialOpen("/dev/ttyACM0", 115200)) < 0)
    {
		fprintf(stderr, "Unable to open serial device: %s\n", strerror(errno));
		return 1 ;
    }

	serialPuts(fd, "#1P2000T1000D100\r\n");
	//Waiting to return OK
	wait_serial_return_ok(fd);
	serialPuts(fd, "#1P1000#2P666T1000D2333\r\n");
	wait_serial_return_ok(fd);
	
	//Test for send wrong instruction
	serialPuts(fd, "#3P2500T9000D9000\r\n");
		
	//Stop wrong instruction
	serialPuts(fd, "~ST");
		
	//Change right instruction
	serialPuts(fd, "#2P2500T9000D9000\r\n");
	wait_serial_return_ok(fd);
		
	//Test for action groups,Group 1 run 3 times
	serialPuts(fd, "G1F3\r\n");
	wait_serial_return_ok(fd);
	
	//Close serial
	serialClose(fd);
	return 0;
}

What leaps out at me from that code is:

1. All commands end with "\r\n".
2. The test program waits for OK to be returned from the serial port

Possibly older user manual here: https://web.archive.org/web/20161213082 ... Manual.pdf