another noob arduino/dynamixel question

[Al_f]

hi all,
I built an arduino based robot that communicated via an xbee radio to matlab on my pc, the servos were simple pwm based ones.

Recently i decided to go for the dynamixel servos (rx-64) for the strength, compliance and feedback. This is where my problems began! I've asked this question on the arduino forum but i think not many of them use these servos.

So the rx-64 uses RS485 for comms, fine, I bought a couple of Max485's and tested the packet creation with an Arduino- Arduino network, the messages come through fine.

Power up the servo and run the simplest program- turning the LED on and off...nothing.

The program seems super simple and as far as I can tell I have sone what the manual said, i'm now stuck! I have looked at the other posts on the forum, but nothing has helped.

Could anyone point me in the right direction, baud I'm using is 57600 on arduino and rx-64 (i believe it is default speed)

Here's the led test code. Any assitance would be massively appreciated.

Code: Select all

//___________________________________________________________
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Arduino to dynamixel via rs485
//___________________________________________________________
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

// Define/preallocate parameters
int i = 0;
byte startAddress;
byte servoID = 0xFE; // 0xFE is broadcast to all servos
byte ledOn = 0x01;
byte ledOff = 0x00;

//___________________________________________________________
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Run setup Function
void setup() {
Serial.begin(57600);
}

//___________________________________________________________
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Run main Function
void loop() {
//Transmission section

if (i%2 ==0){
activateServos(servoID, ledOn);
delay(200);
}else{
activateServos(servoID, ledOff);
delay(200);
}

i++;
if (i>1000){
  i=1;
  }
}

//___________________________________________________________________
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//Function Definitions
//___________________________________________________________________
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


void activateServos (byte servoID, byte newValue){
  unsigned int checksum_ACK;
  byte notchecksum;
  //startAddress = 0X18;     // Enabling torque for first time
  startAddress = 0X19;     // Turning on led
   
  checksum_ACK =  servoID + 0x03 + 0x03 + startAddress + newValue;
  notchecksum = ~checksum_ACK;
 
  digitalWrite(2,HIGH);     // Notify max485 transciever to accept tx
  delay(5);                 // Allow this to take effect
 
  Serial.print(0xFF,BYTE);  // 1.These 2 bytes are 'start message'
  Serial.print(0xFF,BYTE);  // 2.These 2 bytes are 'start message'
  Serial.print(servoID,BYTE);  // 3.ID is target servo or 0xfe which is broadcast mode
  Serial.print(0x03,BYTE);  // 4.Length of string
  Serial.print(0x03,BYTE);  // 5.Ping read write or syncwrite 0x01,2,3,83
  Serial.print(startAddress,BYTE);  // 6.Start address for data to be written
  Serial.print(newValue,BYTE);  //  7.Turning on signal
  Serial.print(notchecksum,BYTE); //8. the notchecksum

 
  delay(200); // allow last byte to go through
  digitalWrite(2,LOW);  // Notify max485 transciever to recieve
}


[i-Bot]

I think the length should be 4 not 3. It should be the number of parameters + 2, memory address counts as one parameter.

[Al_f]

I've got it working now thanks to someone that spotted that I had the length as 0x03 not 0x04 as it should have been, also didn't reset the pin to low. That code will now work if you make those changes.

[Al_f]

thanks i-bot, you noticed it as I was writing the follow-up post. Funnily enough I originally had it as 4 but convinced myself it should be 3 at 2 in the morning when actually i had the + and - signal wires the wrong way round! Working when tired is not a great idea!

Wireless matlab to compliant actuator with a backup controller on the remote microprocessor board suddenly is a possibility.

[Vittorio]

Hi
i also tried this code but using an MX64 with ttl connection
i just changed the address to broadcast 0xfe
since i was not reading but only sending commands i just used the pin tx(1) of the arduino connecting it to the pin data (3) of the motor.
the red led blinks when i connect the motor but i don't get any response to the commands i send.

may it require a different data format?


i have found this manual,
http://support.robotis.com/en/product/d ... /mx-64.htm

but strangely i have not been able from it to understand how a complete command is formatted, do you have any hint? or a simple example to understand if my code is wrong or my motor is broken?

thanks in advance for any hint