RoboSavvy Forum

Trouble with communicating with dynamixels continously

2010-05-13T13:44:08+01:00

yep.
Thanks a lot guys. Seems i need to read more the manual.

btw. After reading and sending data request successfully, I investigated that when requesting the speed data while keep monitoring the speed changes, (every 3 s)only the first coming data is true and the rest is not reliable anymore.
Anyone has any idea? the baudrate is set to 115, 2 kbps not I Mbps.

cheers,

ryann2k1

Statistics: Posted by ryann2k1 — Thu May 13, 2010 1:44 pm

Trouble with communicating with dynamixels continously

2010-04-01T14:45:02+01:00

I took a look at the 8535 manual last night and it appears that you did not post all your code There are registers flags that should be initialized like parity and baud rate.

I agree will Fritzoid UCSRA.7, is a flag that gets set when data is ready in the receive buffer. Anyway, That's how I understand the UCSRA register works from the manual.

This post peaked my interest so I ordered an AVR development board. Should be here in a few days. I'll post my findings.

Statistics: Posted by MikeG — Thu Apr 01, 2010 2:45 pm

Trouble with communicating with dynamixels continously

2010-04-01T13:50:29+01:00

I gave your code another look and this line bothers me...

UCSRA.7 = 1; //Reset RXC with 1

Try commenting-out this line. The RXC flag should be reset by the previous instruction which reads the data from the USART receive buffer (assuming it's now empty). Your code doesn't need to and shouldn't try to set or reset this flag. Could lead to lost data!

Statistics: Posted by Fritzoid — Thu Apr 01, 2010 1:50 pm

Trouble with communicating with dynamixels continously

2010-04-01T13:26:02+01:00

Hi Ryan,

Like Mike said, so far you've shown only shown us the code for a write command. Let's see your read command. Also you've shown us the subroutines, but not the calling sequence. What does main control loop look like?

Finally, the AX-12 manual schematic shows the port direction controlled by a single bit. Yet, your dp_termina() and dp_kirim() are toggling two different bits. Which port is actually connected to the 74HC04? Or is your circuit different, i.e. no inverter at all? We need to know a little more about your hardware setup to be certain the problem isn't in the circuit.

Statistics: Posted by Fritzoid — Thu Apr 01, 2010 1:26 pm

Trouble with communicating with dynamixels continously

2010-04-01T00:23:19+01:00

Sorry; don't know... probably your receive code is has a bug. Maybe someone with better AVR skills can help you debug your code.

Statistics: Posted by MikeG — Thu Apr 01, 2010 12:23 am

Trouble with communicating with dynamixels continously

2010-03-30T05:13:42+01:00

Hi Mike,

My program and circuit work fine when sending any command to dynamixel. I can move the motor to a certain position, I can access the led, etc. But the problems occurred when trying to read the data from dynamixel, I just can get the two FF-FF, while the rest is missing.

Any suggestion?

ryann2k1

Statistics: Posted by ryann2k1 — Tue Mar 30, 2010 5:13 am

Trouble with communicating with dynamixels continously

2010-03-30T04:49:14+01:00

I can't make heads or tails of what you're trying to do. The instruction is writing a 1 to the status return register? Why?

AX-12 come from the manufacturer set to 1Mbps. Unless you changed it to 115.2, it's still set to 1M.

May I suggest that you try lighting the LED on ID 1? That's like the Hello World for AX-12s. If you get the LED to light then you know the connection is good and you can work on capturing the status packet.

Statistics: Posted by MikeG — Tue Mar 30, 2010 4:49 am

communicating with dynamixel

2010-03-30T03:18:18+01:00

Hi Mike,

I am using the UART signal to Half duplex type selector circuit on AX-12 manual page 7.
the programming part :
void terima_serial()
{
while(!UCSRA.7); //Until RXC = 1
datarx [i] =UDR;
UCSRA.7 = 1; //Reset RXC with 1
}

//reset
void reset ()
{
DDRA = 0xFF;
PORTA = 0x00;
}

//direction port
void dp_terima()
{
DDRA = 0xFF;
PORTA = 0x80;
}

void dp_kirim()
{
DDRA = 0xFF;
PORTA= 0x40;
}

Function for reading status:

void baca_read_only1 ()
{
putchar(0xFF);
putchar(0xFF);
putchar(0x01);
putchar(0x04);
putchar(0x03);
putchar(0x10);
putchar(0x01);
putchar(0xE6);
}

The baudrate setting is 115.2 Kbps with clock from crystal 11,0592 MHz for the microcontroller 8535 and the baudrate of the motor is 115.2 Kbps. should it be set to 1 Mbps?
Any idea?

Cheers,

ryann2k1

Statistics: Posted by ryann2k1 — Tue Mar 30, 2010 3:18 am

Trouble with communicating with dynamixels continously

2010-03-29T15:06:31+01:00

Sounds like you have a bug in your code, an error in your circuit, or possibly a bad... AX or RX-XX?

No way to tell from your vague post.

Circuit?
Source code?
Did it ever work?

Statistics: Posted by MikeG — Mon Mar 29, 2010 3:06 pm

communicating with dynamixel

2010-03-29T04:38:02+01:00

Hi All,
I am working now reading the data from dynamixel. with the same circuits, I managed to send data to the dynamixel, but when reading the data, I hardly can grab the data, only the two FF-FF, then the rest is gone.

Any suggestion will be appreciated.

Thank you.

Cheers,

Ryann2k1

Statistics: Posted by ryann2k1 — Mon Mar 29, 2010 4:38 am

Trouble with communicating with dynamixels continously

2010-02-11T16:17:56+01:00

A very important piece of the packet processing framework needs be to resynchronization. A state machine that while waiting for new packets eats bytes until it gets the 0xff 0xff indicating the start of a new packet can be a good solution.

Statistics: Posted by Bullit — Thu Feb 11, 2010 4:17 pm

Trouble with communicating with dynamixels continously

2010-02-11T15:13:04+01:00

rikkov the ideal solution is to fix your receive code so it can gracefully recover. I buffer the received status packets, parse and frame the status packet, discard any bad data, handle the bad data.

Statistics: Posted by MikeG — Thu Feb 11, 2010 3:13 pm

Trouble with communicating with dynamixels continously

2010-02-11T04:27:42+01:00

Thanks a lot for the fast reply!!

I am using a program that we guys wrote,it just keeps writing and reading data to and from dynamixels at 6.9 Hz(for 8 servos).

So as you guys suggested I guess I will have to keep flushing things after each write-read cycle.

Thanks,
Rikkov

Statistics: Posted by rikkov — Thu Feb 11, 2010 4:27 am

Trouble with communicating with dynamixels continously

2010-02-10T17:42:05+01:00

Having worked with most of the different flavors of Robotis servos I can say there is is big difference in communication reliability from TTL to RS485. The TTL servos are prone to all sorts of communications issues. Given that we're talking a single ended, unloaded ttl signal that is 1 mhz on an unshielded network near a bunch of motors and in motion we should be surprised it works at all. The RS485 still has errors but they are considerably more rare.
Rule of thumb: errors happen, clean them up.
As mentioned earlier that's what protocols are for.

Statistics: Posted by Bullit — Wed Feb 10, 2010 5:42 pm

Trouble with communicating with dynamixels continously

2010-02-10T15:45:01+01:00

How often are you getting errors? I've been troubled by random errors with my custom interfaces too. I get an error every couple hundred reads.

I've dealt with the errors by making my code more robust and to just retry when any errors occur. I also always flush both read and write before a read. In the future I want to make my packet parsing a little smarter so it can detect errors earlier and not rely so much on a timeout.

btw. I believe my current timeout is set at 50ms which really is forever, but USB latency really sucks.

Statistics: Posted by billyzelsnack — Wed Feb 10, 2010 3:45 pm