Problem interfacing arbotix-m robocontroller

[Daniel Melia]

Hi,

I'm new using the robotics toolbox. I am using the Arbotix.m function to interface with a physical prototype from Matlab. The robot has an Arbotix-M controller and Dynamixel AX-18 servos. 

I use a code example in Matlab like this to read/write data from/to the servos:

arb=Arbotix('port','COM5', 'nservos',1);         % Establishes a connection with the arbotix-m board

arb.readdata(1,Arbotix.ADDR_POS,2);         % Reads 2-byte current position from servo 1

arb.writedata2(1,Arbotix.ADDR_SPEED,i);   % Sets speed register of servo 1

arb.flush();                                                 % Flash receive buffer

I can implement this instructions one by one using the Matlab command window and I can execute the sequence read/write/flush several times and it works fine. The problem comes when I try to implement this code in an m-file to run it into a loop like this:

for i=100:120

     arb.readdata(1,Arbotix.ADDR_POS,2);        % Reads 2-byte current position from servo 1

     arb.writedata2(1,Arbotix.ADDR_SPEED,i);   % Sets speed register of servo 1

     arb.flush();                                                 % Flash receive buffer

end

In this case Matlab crashes every time I try to run the code and it shows the error message: "Unsuccessful read: the specified amount of data was not returned within the timeout period". The error is found in the code lines:

Arbotix/readdata

     retval=arb.receive();

Arbotix/receive

     c=fread(arb.serPort,1,'uint8');

serial/fread

     Unsuccessful read:

I tried to introduce pauses between instructions and it works better but still crashes from time to time and makes the code slower.

Did anyone have the same problem or know where can it be the error? 

Thanks very much!

[Peter Corke]

It's a long time since I looked at this.  The comms protocol is rather brittle as I recall.  Do you need to do the flush?  Do these commands actually return any information?

Also you should pace the commands to the Arbotix, it will have a finite capacity to process them and send them on to the Dynamixels.

To get smooth paths I recall that I had to load them into the memory of the Arbotix and execute them from there.

Finally, not sure anybody else has ever looked at or used this code.  Maybe this will flush out some other users and we can collectively make something that works.

peter

[Dave Hylands]

I used the following code:
https://gist.github.com/dhylands/73fe96219338eaa8c204

when I did ENG-03.

You can see my videos of the arm moving here:
https://www.youtube.com/watch?v=tZNaBf91Quk
https://www.youtube.com/watch?v=Npi_SXHF_LM
https://www.youtube.com/watch?v=DsrhCSLmoww

In my case I wasn't using the Arbotix at all, just a USB-to-Bioloid bus adapter. Mine was one of my own design, but this would also work:
http://www.trossenrobotics.com/robotis-bioloid-usb2dynamixel.aspx

or this: http://www.trossenrobotics.com/usb2ax

along with this to power the servos:
http://www.trossenrobotics.com/store/p/5886-SMPS2Dynamixel-Adapter.aspx and of course a power supply.

Of course, you can also use the Arbotix.

I also have a full set of python code for controlling the bioloid servos.

Dave Hylands

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Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com

[ashwin.ar...@gmail.com]

Hi there,

I've been having similar issues with the Arbotix class. Doesn't seem to like running things like getpos/setpos/etc within a script but will happily run them through the command window?

[Peter Corke]

I can't fix "doesn't seem to like".  Send me code and error messages.

[ashwin.ar...@gmail.com]

Hi there,

I'm trying to set up a controller for the WidowXL robot arm from Trossen Robotics which uses the Arbotix-M board. 

My code is as simple as:

arb = Arbotix('port','COM4','nservos',5) % Set up a connection

q = arb.getpos() ; % Check position

Which doesn't get results and just times out to this error (whether I run it as a script or in the command line):-

Any ideas what is causing this?

Thanks, Ashwin.

[Peter Corke]

I have zero windows experience, sorry. I have found that the Fddi serial chip takes a while to configure, so try a pause of 10 seconds between open and getpos.