Dynamixel Servos and Labview

[Tim Callinan]

Hello all,

I'm looking for some help with my labview and dynamixel project. I'm building a small robot to greet engineering students at the local community college. I have him built but am getting stuck with the programming. Here is a link to the images of the robot if interested. http://ola2.aacc.edu/tmcallinan/TC_Portfolio_Mick.htm

I'm using labview via a USB Dynamixel to control 8 AX-18 servos. My robot has 2 arms and i'm (trying) to create a program. The left arm is free to move - whatever i do to the left arm i want the right arm to replicate. Im using the dynamixel labview SDK to control the servos. Firstly i open up my COM port then set the max torque and speed for each of the servos. Next i turn the torque OFF for the left and and ON for the right arm. In the main section of the program (its in a while loop) I'm reading what the positions of the left arm are and setting the desired position of the right arm to these numbers.

What happens:  The right arm will follow whatever i do to the left arm - For about 5-6 seconds and then nothing - i need to restart the program. I think the problem is with the USB dynamixel. I'm sending and receiving too much data for it to handle? Im thinking this because if i put a delay in the loop say 500ms it keeps on working. 

Maybe there is someone out there who has done this before and can see my mistake or give us a bit of advice. Any help is appreciated.

Thanks - Tim

[Joel Khan]

Tim,

I took a brief look at your VI. It seems a bit complex, I have yet to look at it with the dynamixel driver installed but I would recomend making the VI as simple as possible in order to reduce the chance that the behavior you are seeing is due to programing problems.Have you tried running your program in highligh execuition mode? If you continue to have issues and are certain its the USB dynamixel hardware/ driver having issues I would recomend contacting Dynamixel.

<Joel Khan | Applications Engineering | National Instruments | Rice University BSEE>  

[josborne]

Hi Tim,

I am having the EXACT same problem! 

I am also using a USB Dynamixel and the same SDK.  But I am using the AX-18F servos.

My program will work perfectly fine for a while ... and then hang.  I end up power-cycling the servo to fix the problem.

did you ever find a fix for this?

I also agree that it is probably a timing issue.  But adding wait statements never fixed my problem.  I need to update the position fairly quickly, and I am guessing this is causing the problem.

[Tim Callinan]

Hi Josborne,

Yeah it sucks big-time. I've moved on to another project but i couldnt get it working. I had to power cycle all the servos. I had 10 servos on the one usb dynamixel.

Im sorry i have no answer for you. If you figure it out - please update. 

- Tim

[josborne]

Voila!

I think I found the solution.  I did some googling, and stumbled upon this configuration page regarding the USB2Dynamixel:

http://support.robotis.com/en/software/dynamixel_sdk/usb2dynamixel/usb2dxl_windows.htm

Towards the bottom of the page, it tells you to adjust the Response Time Adjustment in the Windows Device Manager.  Its some sort of latency timer that can be lowered to correct communication problems.  By lowering the value to 1, as indicated, my problem was solved.  Just ran a bunch of tests and it works great now!