This · is · Not · a · Brain · Surgery

In my last post I have described OWI-007 Robotic Arm parallel port protocol. They have a newer, more advanced model called Robotic Arm Edge:



You can use USB interface module to connect it to PC. Unfortunately official software works only under Windows and do not provide API. I have been able to reverse engineer their USB protocol and write sample code which allows to control the arm from Mac and Linux.

This is USB device with vendor id 0x1267 and product id 0. The device is controlled by 3 byte commands sent via USB control transfers. Command format is byte0, byte1, byte2. Each byte controls a group of arm features. All motors could be controlled independently. Most commands start action which is continued until next action is signalled. Byte '00' universally used as stop action.

Bit numbering in byte:

7 (most significant)

6

5

4

3

2

1

0 (least significant)

Meaning of bits in each byte:

Byte 0

First byte controls grip, shoulder and wrist. Bits are assigned as following:

Bit numbers	Controls	Bit combinations
0,1	Grip	00-do not move, 01-close, 10-open
2,3	Wrist	00-do not move, 01-move up, 10-move down
4,5	Elbow	00-do not move, 01-move up, 10-move down
6,7	Shoulder	00-do not move, 01-move up, 10-move down

Sample commands, activating single motor:

Byte 0	Command
00	stop grip, wrist, elbow and shoulder movement
01	grip close
02	grip open
04	wrist up
08	wrist down
10	elbow up
20	elbow down
40	shoulder up
80	shoulder down

Sample commands activating 2 motors simultaneously:

Byte 0	Command
11	grip close and elbow up
82	grip open and shoulder down

Byte1

Second byte controls base.
Bits are assigned as following:

Bit numbers	Controls	Bit combinations
0,1	Base	00-do not move, 01-rotate clockwise, 10-rotate counter-clocwise

Sample commands:

Byte 1	Command
00	stop base rotation
01	rotate base clockwise
02	rotate base counter-clocwise

Byte 2

Third byte controls LED light inside the grip.
Bits are assigned as following:

Bit numbers	Controls	Bit combinations
0	LED	0-off, 1-on

Sample commands:

Byte 2	Command
00	LED off
01	LED on

Sample source code using libusb:

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <string.h>

#include <libusb-1.0/libusb.h>

#define EP_INTR	(1 | LIBUSB_ENDPOINT_IN)

#define ARM_VENDOR       0x1267
#define ARM_PRODUCT      0
#define CMD_DATALEN      3

libusb_device * find_arm(libusb_device **devs)
{
	libusb_device *dev;
	int i = 0;

	while ((dev = devs[i++]) != NULL) {
		struct libusb_device_descriptor desc;
		int r = libusb_get_device_descriptor(dev, &desc);
		if (r < 0) {
			fprintf(stderr, "failed to get device descriptor");
			return NULL;
		}
		if(desc.idVendor == ARM_VENDOR &&
		   desc.idProduct == ARM_PRODUCT)
		  {
		    return dev;
		  }
	}
	return NULL;
}

int main(int ac, char **av)
{
    if(ac!=4)
    {
        fprintf(stderr,"Usage: armedgetest CMD0 CMD1 CMD2\n");
        return 1;
    }

    unsigned char cmd[3];

    cmd[0]=(unsigned char)strtol(av[1],NULL,16);
    cmd[1]=(unsigned char)strtol(av[2],NULL,16);
    cmd[2]=(unsigned char)strtol(av[3],NULL,16);
    
	libusb_device **devs;
    libusb_device *dev;
    struct libusb_device_handle *devh = NULL;
	int r;
	ssize_t cnt;

	r = libusb_init(NULL);
	if (r < 0)
    {
	    fprintf(stderr, "failed to initialize libusb\n");
	    return r;
    }

    libusb_set_debug(NULL,2);
    
	cnt = libusb_get_device_list(NULL, &devs);
	if (cnt < 0)
		return (int) cnt;
    dev=find_arm(devs);
    if(!dev)
    {
	    fprintf(stderr, "Robot Arm not found\n");
	    return -1;
    }

    r = libusb_open(dev,&devh);
    if(r!=0)
    {
	    fprintf(stderr, "Error opening device\n");
       	    libusb_free_device_list(devs, 1);
             libusb_exit(NULL);
	    return -1;
    }


    fprintf(stderr, "Sending %02X %02X %02X\n",
            (int)cmd[0],
            (int)cmd[1],
            (int)cmd[2]
    );

    int actual_length=-1;
    
    r = libusb_control_transfer(devh,
                                0x40, //uint8_t 	bmRequestType,
                                6, //uint8_t 	bRequest,
                                0x100, //uint16_t 	wValue,
                                0,//uint16_t 	wIndex,
                                cmd,
                                CMD_DATALEN,
                                0	 
    );
    
    if(!(r == 0 && actual_length >= CMD_DATALEN))
    {
        fprintf(stderr, "Write err %d. len=%d\n",r,actual_length);
    }
    
    libusb_close(devh);
	libusb_free_device_list(devs, 1);
	libusb_exit(NULL);

    fprintf(stderr, "Done\n");
	return 0;
}

Sample usage:

./armedgetest 00 00 01
sleep 3
./armedgetest 00 00 00

will turn the light on for 3 seconds and then would turn it off. It have been tested on MacOS X, but should work on Linux as well.