Dynamixel Communication

 
#1

Hello, I am slightly confused about which protocol is needed to run dynamixel servos. I purchased a few ax12 a servos for lower strength applications, but I'm also interested in an mx 64 t or 64 r which appears to be either ttl or rs 485 protocols. Which protocol does port d5 on the ezb 4 use. I read some posts from old bit builder , he was using ax 12a as well. The picture on the plugin page has a rx 64 servo shown which I thought used a completely separate protocol. Very confusing. I would like to be able to daisy chain elbow rotation, elbow flex, and wrist rotation servos together in a ax12a, mx64xx, ax12a layout. Thanks for the help.

#2

@kamaronman68,

For AX-12 servos use 'Dynamixel Type Protocol_1'.
You will need to set the baud rate of the servo to 117647 which is register 4 value 16. That baud rte is close enough to 115200 to work.

I used a Robotis USB2DYNAMIXEL device to set the baud rate, then the EZ-B Dynamixel plugin to set the ID of each servo.

Good luck.

#3

Out of curiosity, does anyone know if robotis actually has a support forum or any form of support? It seems ezrobot is having to address their support issues often. It would be nice to see robotis put effort toward their customer. Strange...

#4

Trossen Robotics has a forum:
forums.trossenrobotics.com/forumdisplay.php?22-Robotics
Topics of special interest include: Humanoids, Walkers & Crawlers, Dynamixel & Robot Actuators, and more.

Robotis does have an online manual set that covers all of their products. Getting to the information is a bit hard. The manual is at support.robotis.com/en/
You will need to drill down their subject tree to expand the topics:
Product Information --> Dynamixel

Good luck!

#5

Actually what I was asking is what protocol comes out of the ezb4 d5 port? This is to make sure the bigger servos I buy next are compatible . Is the protocol rs485 or ttl serial?

#6

D5 is UART port 1 by coincidence... however you can send serial from any port on the EZB. Which in this context is TTL... D6 (UART port 1 receive) would be serial receive... So all this means is you can send serial commands to you dynamixels from any port on the EZB... you don't need to use D5...

#7

ttl - there must be some documentation on the protocols from robotis somewhere on the internet. Here's the information we provide for the plugin: http://www.ez-robot.com/EZ-Builder/Plugins/view/39

There is reference to the UART being used - which also transmits 485 but only one direction as ttl. The plugin is not 485 bi-directional compatible, which means you would require additional hardware to receive data and split the dynamixel's tx to the ez-b rx. To make it simple, and since robotis has been the least supportive with zero communication company that we have ever dealt with, the plugin is limited to ez-b tx.

I have emailed the source code of the plugin to robotis representatives to get them started and create an official plugin.... I've yet to receive a response.

#8

Thank you

#9

@DJ Hmmm... Didn't know it had to be port D5 (UART). I though you can send commands to dynamixels over any port? Is that because of higher baud speed or is it just something you arbitrarily "hardwired" into the dynamixel control in the plugin?

#10

Because of the baud rate.