Programming for AX-12

[Starlight]

Hi all. currently I'm writing moving position for sync write. I'm using PIC18F4550, and for single dynamixel, it perform well. By the way, I wanna control up to 14 number of dynamixel, so it will waste a lots of time to calculate the checksum. So I came up with the following code:
(control only 2 number of dynamixel)

*******MOVING POSITION (SYNC WRITE)***********
uart_send(0xFF);
uart_send(0xFF);
uart_send(0xFE);
uart_send(0x0E); //LENGTH = (L+1)*N+4
uart_send(0x83);
uart_send(0x1E); //goal position
uart_send(0x04); //length of data to be written (1 dynamixel)
sendSW(1,0x0010,0x0150);
checksum_1 = sendSW (1,0x0010,0x0150);
sendSW(2,0x0220,0x0360);
checksum_2 = sendSW (2,0x0220,0x0360);
t_checksum = checksum_1 + checksum_2;
uart_send(0x4E+t_checksum); //total checksum

char sendSW (char id, int pos, int speed)
{
uart_send(id); //ID
uart_send((char)pos);
uart_send((char)(pos>>8));
uart_send((char)speed); //Moving Speed
uart_send((char)(speed>>8));
return(~(char)(id+(char)pos+(char)(pos>>8)+(char)speed+(char)(speed>>8))); //checksum
}

But it seem not exactly corret, is there any error or mistake in calculating the return value of checksum ?

Or have anyone came out with better method for controlling up to 14 number of dynamixel without wasting lots of time in calculating the checksum and reduce the line of programming ?

Thanks !

[StuartL]

Or have anyone came out with better method for controlling up to 14 number of dynamixel without wasting lots of time in calculating the checksum and reduce the line of programming ?

The way we do it in libbioloid (check out the other threads on this) is to have a function to send the start of a packet, a function to send packet data and a function to send the end of a packet.

The logic goes something like this:

Code: Select all

uint8_t packetchecksum;

void packet_start(uint8_t id, uint8_t length) {
   checksum = id + length;
   uart_send(0xff);
   uart_send(0xff);
   uart_send(id);
   uart_send(length);
}

void packet_data(uint8_t *data, uint8_t length) {
   uint8_t count = length;
   uint8_t *ptr = data;
   while (count--) {
      uart_send(*ptr);
      checksum += *ptr;
      ptr++;
   }
}

void packet_end(void) {
   uart_send(~checksum);
}

void send_ping(uint8_t id) {
   packet_start(id, PING_LENGTH);
   packet_data(PING_DATA, PING_DATALENGTH);
   packet_end();
}


Please don't use the code above as-is without sanity checking it, it's written off the top of my head and probably has many bugs. It's more to illustrate a point

[Starlight]

Hi. May I ask how to implementing a continuously rotating wheel ? from the manual, it state that set the CW and CCW angle limit to 0. then set the Goal Speed.

uart_send(0xff);
uart_send(0xff);
uart_send(0x0d); //ID
uart_send(0x07); //length
uart_send(0x03); //write_data
uart_send(0x06); //starting address: CW angle limit
uart_send(0x00); //CW angle limit
uart_send(0x00);
uart_send(0x00); //CCW angle limit
uart_send(0x00);
uart_send(0xe9); //checksum

~~waiting for transmit


uart_send(0xff);
uart_send(0xff);
uart_send(0x0d); //ID
uart_send(0x05); //length
uart_send(0x03); //write data
uart_send(0x20); //starting address: moving speed
uart_send(0x50);
uart_send(0x01);
uart_send(0x79); //checksum

while(TXSTAbits.TRMT==0);

LATCbits.LATC0 =1;

So the above code is the correct one?

[Starlight]

uint8_t packetchecksum;

void packet_start(uint8_t id, uint8_t length) {
checksum = id + length;
uart_send(0xff);
uart_send(0xff);
uart_send(id);
uart_send(length);
}

void packet_data(uint8_t *data, uint8_t length) {
uint8_t count = length;
uint8_t *ptr = data;
while (count--) {
uart_send(*ptr);
checksum += *ptr;
ptr++;
}
}

void packet_end(void) {
uart_send(~checksum);
}

void send_ping(uint8_t id) {
packet_start(id, PING_LENGTH);
packet_data(PING_DATA, PING_DATALENGTH);
packet_end();
}

is that the above code controlling 1 dynamixel ? I wanna control up to 14 dynamixel on the same time for sync write. from the user manual page 23, there is more like instruction(0x83), ID(0xfe), .etc.

[Starlight]

Hi all. I have another question about the time delay of programming. As I know that Ax-12 have the feedback position, so how can I using this kind of method? let say I have movement1 and movement2. after the execution of movement1, wait for about 2 second, the movement2 are execute. So how we write this kind of programming using the feedback position of movement1, confirm the position of movement1(executed), then execute movement2 ? Thanks.